Commit 5ebdc8c46c

joachimschmidt557 <joachim.schmidt557@outlook.com>
2021-11-02 17:18:54
stage2 RISCV64: move codegen to separate file
1 parent 674932e
Changed files (2)
src
src/arch/riscv64/CodeGen.zig
@@ -0,0 +1,2165 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const mem = std.mem;
+const math = std.math;
+const assert = std.debug.assert;
+const Air = @import("../../Air.zig");
+const Zir = @import("../../Zir.zig");
+const Liveness = @import("../../Liveness.zig");
+const Type = @import("../../type.zig").Type;
+const Value = @import("../../value.zig").Value;
+const TypedValue = @import("../../TypedValue.zig");
+const link = @import("../../link.zig");
+const Module = @import("../../Module.zig");
+const Compilation = @import("../../Compilation.zig");
+const ErrorMsg = Module.ErrorMsg;
+const Target = std.Target;
+const Allocator = mem.Allocator;
+const trace = @import("../../tracy.zig").trace;
+const DW = std.dwarf;
+const leb128 = std.leb;
+const log = std.log.scoped(.codegen);
+const build_options = @import("build_options");
+const RegisterManager = @import("../../register_manager.zig").RegisterManager;
+
+const FnResult = @import("../../codegen.zig").FnResult;
+const GenerateSymbolError = @import("../../codegen.zig").GenerateSymbolError;
+const DebugInfoOutput = @import("../../codegen.zig").DebugInfoOutput;
+
+const InnerError = error{
+    OutOfMemory,
+    CodegenFail,
+};
+
+gpa: *Allocator,
+air: Air,
+liveness: Liveness,
+bin_file: *link.File,
+target: *const std.Target,
+mod_fn: *const Module.Fn,
+code: *std.ArrayList(u8),
+debug_output: DebugInfoOutput,
+err_msg: ?*ErrorMsg,
+args: []MCValue,
+ret_mcv: MCValue,
+fn_type: Type,
+arg_index: usize,
+src_loc: Module.SrcLoc,
+stack_align: u32,
+
+prev_di_line: u32,
+prev_di_column: u32,
+/// Byte offset within the source file of the ending curly.
+end_di_line: u32,
+end_di_column: u32,
+/// Relative to the beginning of `code`.
+prev_di_pc: usize,
+
+/// The value is an offset into the `Function` `code` from the beginning.
+/// To perform the reloc, write 32-bit signed little-endian integer
+/// which is a relative jump, based on the address following the reloc.
+exitlude_jump_relocs: std.ArrayListUnmanaged(usize) = .{},
+
+/// Whenever there is a runtime branch, we push a Branch onto this stack,
+/// and pop it off when the runtime branch joins. This provides an "overlay"
+/// of the table of mappings from instructions to `MCValue` from within the branch.
+/// This way we can modify the `MCValue` for an instruction in different ways
+/// within different branches. Special consideration is needed when a branch
+/// joins with its parent, to make sure all instructions have the same MCValue
+/// across each runtime branch upon joining.
+branch_stack: *std.ArrayList(Branch),
+
+// Key is the block instruction
+blocks: std.AutoHashMapUnmanaged(Air.Inst.Index, BlockData) = .{},
+
+register_manager: RegisterManager(Self, Register, &callee_preserved_regs) = .{},
+/// Maps offset to what is stored there.
+stack: std.AutoHashMapUnmanaged(u32, StackAllocation) = .{},
+
+/// Offset from the stack base, representing the end of the stack frame.
+max_end_stack: u32 = 0,
+/// Represents the current end stack offset. If there is no existing slot
+/// to place a new stack allocation, it goes here, and then bumps `max_end_stack`.
+next_stack_offset: u32 = 0,
+
+/// Debug field, used to find bugs in the compiler.
+air_bookkeeping: @TypeOf(air_bookkeeping_init) = air_bookkeeping_init,
+
+const air_bookkeeping_init = if (std.debug.runtime_safety) @as(usize, 0) else {};
+
+const MCValue = union(enum) {
+    /// No runtime bits. `void` types, empty structs, u0, enums with 1 tag, etc.
+    /// TODO Look into deleting this tag and using `dead` instead, since every use
+    /// of MCValue.none should be instead looking at the type and noticing it is 0 bits.
+    none,
+    /// Control flow will not allow this value to be observed.
+    unreach,
+    /// No more references to this value remain.
+    dead,
+    /// The value is undefined.
+    undef,
+    /// A pointer-sized integer that fits in a register.
+    /// If the type is a pointer, this is the pointer address in virtual address space.
+    immediate: u64,
+    /// The constant was emitted into the code, at this offset.
+    /// If the type is a pointer, it means the pointer address is embedded in the code.
+    embedded_in_code: usize,
+    /// The value is a pointer to a constant which was emitted into the code, at this offset.
+    ptr_embedded_in_code: usize,
+    /// The value is in a target-specific register.
+    register: Register,
+    /// The value is in memory at a hard-coded address.
+    /// If the type is a pointer, it means the pointer address is at this memory location.
+    memory: u64,
+    /// The value is one of the stack variables.
+    /// If the type is a pointer, it means the pointer address is in the stack at this offset.
+    stack_offset: u32,
+    /// The value is a pointer to one of the stack variables (payload is stack offset).
+    ptr_stack_offset: u32,
+    /// The value is in the compare flags assuming an unsigned operation,
+    /// with this operator applied on top of it.
+    compare_flags_unsigned: math.CompareOperator,
+    /// The value is in the compare flags assuming a signed operation,
+    /// with this operator applied on top of it.
+    compare_flags_signed: math.CompareOperator,
+
+    fn isMemory(mcv: MCValue) bool {
+        return switch (mcv) {
+            .embedded_in_code, .memory, .stack_offset => true,
+            else => false,
+        };
+    }
+
+    fn isImmediate(mcv: MCValue) bool {
+        return switch (mcv) {
+            .immediate => true,
+            else => false,
+        };
+    }
+
+    fn isMutable(mcv: MCValue) bool {
+        return switch (mcv) {
+            .none => unreachable,
+            .unreach => unreachable,
+            .dead => unreachable,
+
+            .immediate,
+            .embedded_in_code,
+            .memory,
+            .compare_flags_unsigned,
+            .compare_flags_signed,
+            .ptr_stack_offset,
+            .ptr_embedded_in_code,
+            .undef,
+            => false,
+
+            .register,
+            .stack_offset,
+            => true,
+        };
+    }
+};
+
+const Branch = struct {
+    inst_table: std.AutoArrayHashMapUnmanaged(Air.Inst.Index, MCValue) = .{},
+
+    fn deinit(self: *Branch, gpa: *Allocator) void {
+        self.inst_table.deinit(gpa);
+        self.* = undefined;
+    }
+};
+
+const StackAllocation = struct {
+    inst: Air.Inst.Index,
+    /// TODO do we need size? should be determined by inst.ty.abiSize()
+    size: u32,
+};
+
+const BlockData = struct {
+    relocs: std.ArrayListUnmanaged(Reloc),
+    /// The first break instruction encounters `null` here and chooses a
+    /// machine code value for the block result, populating this field.
+    /// Following break instructions encounter that value and use it for
+    /// the location to store their block results.
+    mcv: MCValue,
+};
+
+const Reloc = union(enum) {
+    /// The value is an offset into the `Function` `code` from the beginning.
+    /// To perform the reloc, write 32-bit signed little-endian integer
+    /// which is a relative jump, based on the address following the reloc.
+    rel32: usize,
+    /// A branch in the ARM instruction set
+    arm_branch: struct {
+        pos: usize,
+        cond: @import("../arm/bits.zig").Condition,
+    },
+};
+
+const BigTomb = struct {
+    function: *Self,
+    inst: Air.Inst.Index,
+    tomb_bits: Liveness.Bpi,
+    big_tomb_bits: u32,
+    bit_index: usize,
+
+    fn feed(bt: *BigTomb, op_ref: Air.Inst.Ref) void {
+        const this_bit_index = bt.bit_index;
+        bt.bit_index += 1;
+
+        const op_int = @enumToInt(op_ref);
+        if (op_int < Air.Inst.Ref.typed_value_map.len) return;
+        const op_index = @intCast(Air.Inst.Index, op_int - Air.Inst.Ref.typed_value_map.len);
+
+        if (this_bit_index < Liveness.bpi - 1) {
+            const dies = @truncate(u1, bt.tomb_bits >> @intCast(Liveness.OperandInt, this_bit_index)) != 0;
+            if (!dies) return;
+        } else {
+            const big_bit_index = @intCast(u5, this_bit_index - (Liveness.bpi - 1));
+            const dies = @truncate(u1, bt.big_tomb_bits >> big_bit_index) != 0;
+            if (!dies) return;
+        }
+        bt.function.processDeath(op_index);
+    }
+
+    fn finishAir(bt: *BigTomb, result: MCValue) void {
+        const is_used = !bt.function.liveness.isUnused(bt.inst);
+        if (is_used) {
+            log.debug("%{d} => {}", .{ bt.inst, result });
+            const branch = &bt.function.branch_stack.items[bt.function.branch_stack.items.len - 1];
+            branch.inst_table.putAssumeCapacityNoClobber(bt.inst, result);
+        }
+        bt.function.finishAirBookkeeping();
+    }
+};
+
+const Self = @This();
+
+pub fn generate(
+    bin_file: *link.File,
+    src_loc: Module.SrcLoc,
+    module_fn: *Module.Fn,
+    air: Air,
+    liveness: Liveness,
+    code: *std.ArrayList(u8),
+    debug_output: DebugInfoOutput,
+) GenerateSymbolError!FnResult {
+    if (build_options.skip_non_native and builtin.cpu.arch != bin_file.options.target.cpu.arch) {
+        @panic("Attempted to compile for architecture that was disabled by build configuration");
+    }
+
+    assert(module_fn.owner_decl.has_tv);
+    const fn_type = module_fn.owner_decl.ty;
+
+    var branch_stack = std.ArrayList(Branch).init(bin_file.allocator);
+    defer {
+        assert(branch_stack.items.len == 1);
+        branch_stack.items[0].deinit(bin_file.allocator);
+        branch_stack.deinit();
+    }
+    try branch_stack.append(.{});
+
+    var function = Self{
+        .gpa = bin_file.allocator,
+        .air = air,
+        .liveness = liveness,
+        .target = &bin_file.options.target,
+        .bin_file = bin_file,
+        .mod_fn = module_fn,
+        .code = code,
+        .debug_output = debug_output,
+        .err_msg = null,
+        .args = undefined, // populated after `resolveCallingConventionValues`
+        .ret_mcv = undefined, // populated after `resolveCallingConventionValues`
+        .fn_type = fn_type,
+        .arg_index = 0,
+        .branch_stack = &branch_stack,
+        .src_loc = src_loc,
+        .stack_align = undefined,
+        .prev_di_pc = 0,
+        .prev_di_line = module_fn.lbrace_line,
+        .prev_di_column = module_fn.lbrace_column,
+        .end_di_line = module_fn.rbrace_line,
+        .end_di_column = module_fn.rbrace_column,
+    };
+    defer function.stack.deinit(bin_file.allocator);
+    defer function.blocks.deinit(bin_file.allocator);
+    defer function.exitlude_jump_relocs.deinit(bin_file.allocator);
+
+    var call_info = function.resolveCallingConventionValues(fn_type) catch |err| switch (err) {
+        error.CodegenFail => return FnResult{ .fail = function.err_msg.? },
+        else => |e| return e,
+    };
+    defer call_info.deinit(&function);
+
+    function.args = call_info.args;
+    function.ret_mcv = call_info.return_value;
+    function.stack_align = call_info.stack_align;
+    function.max_end_stack = call_info.stack_byte_count;
+
+    function.gen() catch |err| switch (err) {
+        error.CodegenFail => return FnResult{ .fail = function.err_msg.? },
+        else => |e| return e,
+    };
+
+    if (function.err_msg) |em| {
+        return FnResult{ .fail = em };
+    } else {
+        return FnResult{ .appended = {} };
+    }
+}
+
+fn gen(self: *Self) !void {
+    try self.dbgSetPrologueEnd();
+    try self.genBody(self.air.getMainBody());
+    try self.dbgSetEpilogueBegin();
+
+    // Drop them off at the rbrace.
+    try self.dbgAdvancePCAndLine(self.end_di_line, self.end_di_column);
+}
+
+fn genBody(self: *Self, body: []const Air.Inst.Index) InnerError!void {
+    const air_tags = self.air.instructions.items(.tag);
+
+    for (body) |inst| {
+        const old_air_bookkeeping = self.air_bookkeeping;
+        try self.ensureProcessDeathCapacity(Liveness.bpi);
+
+        switch (air_tags[inst]) {
+            // zig fmt: off
+                    .add, .ptr_add   => try self.airAdd(inst),
+                    .addwrap         => try self.airAddWrap(inst),
+                    .add_sat         => try self.airAddSat(inst),
+                    .sub, .ptr_sub   => try self.airSub(inst),
+                    .subwrap         => try self.airSubWrap(inst),
+                    .sub_sat         => try self.airSubSat(inst),
+                    .mul             => try self.airMul(inst),
+                    .mulwrap         => try self.airMulWrap(inst),
+                    .mul_sat         => try self.airMulSat(inst),
+                    .rem             => try self.airRem(inst),
+                    .mod             => try self.airMod(inst),
+                    .shl, .shl_exact => try self.airShl(inst),
+                    .shl_sat         => try self.airShlSat(inst),
+                    .min             => try self.airMin(inst),
+                    .max             => try self.airMax(inst),
+                    .slice           => try self.airSlice(inst),
+
+                    .div_float, .div_trunc, .div_floor, .div_exact => try self.airDiv(inst),
+
+                    .cmp_lt  => try self.airCmp(inst, .lt),
+                    .cmp_lte => try self.airCmp(inst, .lte),
+                    .cmp_eq  => try self.airCmp(inst, .eq),
+                    .cmp_gte => try self.airCmp(inst, .gte),
+                    .cmp_gt  => try self.airCmp(inst, .gt),
+                    .cmp_neq => try self.airCmp(inst, .neq),
+
+                    .bool_and => try self.airBoolOp(inst),
+                    .bool_or  => try self.airBoolOp(inst),
+                    .bit_and  => try self.airBitAnd(inst),
+                    .bit_or   => try self.airBitOr(inst),
+                    .xor      => try self.airXor(inst),
+                    .shr      => try self.airShr(inst),
+
+                    .alloc           => try self.airAlloc(inst),
+                    .ret_ptr         => try self.airRetPtr(inst),
+                    .arg             => try self.airArg(inst),
+                    .assembly        => try self.airAsm(inst),
+                    .bitcast         => try self.airBitCast(inst),
+                    .block           => try self.airBlock(inst),
+                    .br              => try self.airBr(inst),
+                    .breakpoint      => try self.airBreakpoint(),
+                    .fence           => try self.airFence(),
+                    .call            => try self.airCall(inst),
+                    .cond_br         => try self.airCondBr(inst),
+                    .dbg_stmt        => try self.airDbgStmt(inst),
+                    .fptrunc         => try self.airFptrunc(inst),
+                    .fpext           => try self.airFpext(inst),
+                    .intcast         => try self.airIntCast(inst),
+                    .trunc           => try self.airTrunc(inst),
+                    .bool_to_int     => try self.airBoolToInt(inst),
+                    .is_non_null     => try self.airIsNonNull(inst),
+                    .is_non_null_ptr => try self.airIsNonNullPtr(inst),
+                    .is_null         => try self.airIsNull(inst),
+                    .is_null_ptr     => try self.airIsNullPtr(inst),
+                    .is_non_err      => try self.airIsNonErr(inst),
+                    .is_non_err_ptr  => try self.airIsNonErrPtr(inst),
+                    .is_err          => try self.airIsErr(inst),
+                    .is_err_ptr      => try self.airIsErrPtr(inst),
+                    .load            => try self.airLoad(inst),
+                    .loop            => try self.airLoop(inst),
+                    .not             => try self.airNot(inst),
+                    .ptrtoint        => try self.airPtrToInt(inst),
+                    .ret             => try self.airRet(inst),
+                    .ret_load        => try self.airRetLoad(inst),
+                    .store           => try self.airStore(inst),
+                    .struct_field_ptr=> try self.airStructFieldPtr(inst),
+                    .struct_field_val=> try self.airStructFieldVal(inst),
+                    .array_to_slice  => try self.airArrayToSlice(inst),
+                    .int_to_float    => try self.airIntToFloat(inst),
+                    .float_to_int    => try self.airFloatToInt(inst),
+                    .cmpxchg_strong  => try self.airCmpxchg(inst),
+                    .cmpxchg_weak    => try self.airCmpxchg(inst),
+                    .atomic_rmw      => try self.airAtomicRmw(inst),
+                    .atomic_load     => try self.airAtomicLoad(inst),
+                    .memcpy          => try self.airMemcpy(inst),
+                    .memset          => try self.airMemset(inst),
+                    .set_union_tag   => try self.airSetUnionTag(inst),
+                    .get_union_tag   => try self.airGetUnionTag(inst),
+                    .clz             => try self.airClz(inst),
+                    .ctz             => try self.airCtz(inst),
+                    .popcount        => try self.airPopcount(inst),
+
+                    .atomic_store_unordered => try self.airAtomicStore(inst, .Unordered),
+                    .atomic_store_monotonic => try self.airAtomicStore(inst, .Monotonic),
+                    .atomic_store_release   => try self.airAtomicStore(inst, .Release),
+                    .atomic_store_seq_cst   => try self.airAtomicStore(inst, .SeqCst),
+
+                    .struct_field_ptr_index_0 => try self.airStructFieldPtrIndex(inst, 0),
+                    .struct_field_ptr_index_1 => try self.airStructFieldPtrIndex(inst, 1),
+                    .struct_field_ptr_index_2 => try self.airStructFieldPtrIndex(inst, 2),
+                    .struct_field_ptr_index_3 => try self.airStructFieldPtrIndex(inst, 3),
+
+                    .switch_br       => try self.airSwitch(inst),
+                    .slice_ptr       => try self.airSlicePtr(inst),
+                    .slice_len       => try self.airSliceLen(inst),
+
+                    .ptr_slice_len_ptr => try self.airPtrSliceLenPtr(inst),
+                    .ptr_slice_ptr_ptr => try self.airPtrSlicePtrPtr(inst),
+
+                    .array_elem_val      => try self.airArrayElemVal(inst),
+                    .slice_elem_val      => try self.airSliceElemVal(inst),
+                    .slice_elem_ptr      => try self.airSliceElemPtr(inst),
+                    .ptr_elem_val        => try self.airPtrElemVal(inst),
+                    .ptr_elem_ptr        => try self.airPtrElemPtr(inst),
+
+                    .constant => unreachable, // excluded from function bodies
+                    .const_ty => unreachable, // excluded from function bodies
+                    .unreach  => self.finishAirBookkeeping(),
+
+                    .optional_payload           => try self.airOptionalPayload(inst),
+                    .optional_payload_ptr       => try self.airOptionalPayloadPtr(inst),
+                    .unwrap_errunion_err        => try self.airUnwrapErrErr(inst),
+                    .unwrap_errunion_payload    => try self.airUnwrapErrPayload(inst),
+                    .unwrap_errunion_err_ptr    => try self.airUnwrapErrErrPtr(inst),
+                    .unwrap_errunion_payload_ptr=> try self.airUnwrapErrPayloadPtr(inst),
+
+                    .wrap_optional         => try self.airWrapOptional(inst),
+                    .wrap_errunion_payload => try self.airWrapErrUnionPayload(inst),
+                    .wrap_errunion_err     => try self.airWrapErrUnionErr(inst),
+                    // zig fmt: on
+        }
+        if (std.debug.runtime_safety) {
+            if (self.air_bookkeeping < old_air_bookkeeping + 1) {
+                std.debug.panic("in codegen.zig, handling of AIR instruction %{d} ('{}') did not do proper bookkeeping. Look for a missing call to finishAir.", .{ inst, air_tags[inst] });
+            }
+        }
+    }
+}
+
+fn dbgSetPrologueEnd(self: *Self) InnerError!void {
+    switch (self.debug_output) {
+        .dwarf => |dbg_out| {
+            try dbg_out.dbg_line.append(DW.LNS.set_prologue_end);
+            try self.dbgAdvancePCAndLine(self.prev_di_line, self.prev_di_column);
+        },
+        .plan9 => {},
+        .none => {},
+    }
+}
+
+fn dbgSetEpilogueBegin(self: *Self) InnerError!void {
+    switch (self.debug_output) {
+        .dwarf => |dbg_out| {
+            try dbg_out.dbg_line.append(DW.LNS.set_epilogue_begin);
+            try self.dbgAdvancePCAndLine(self.prev_di_line, self.prev_di_column);
+        },
+        .plan9 => {},
+        .none => {},
+    }
+}
+
+fn dbgAdvancePCAndLine(self: *Self, line: u32, column: u32) InnerError!void {
+    const delta_line = @intCast(i32, line) - @intCast(i32, self.prev_di_line);
+    const delta_pc: usize = self.code.items.len - self.prev_di_pc;
+    switch (self.debug_output) {
+        .dwarf => |dbg_out| {
+            // TODO Look into using the DWARF special opcodes to compress this data.
+            // It lets you emit single-byte opcodes that add different numbers to
+            // both the PC and the line number at the same time.
+            try dbg_out.dbg_line.ensureUnusedCapacity(11);
+            dbg_out.dbg_line.appendAssumeCapacity(DW.LNS.advance_pc);
+            leb128.writeULEB128(dbg_out.dbg_line.writer(), delta_pc) catch unreachable;
+            if (delta_line != 0) {
+                dbg_out.dbg_line.appendAssumeCapacity(DW.LNS.advance_line);
+                leb128.writeILEB128(dbg_out.dbg_line.writer(), delta_line) catch unreachable;
+            }
+            dbg_out.dbg_line.appendAssumeCapacity(DW.LNS.copy);
+            self.prev_di_pc = self.code.items.len;
+            self.prev_di_line = line;
+            self.prev_di_column = column;
+            self.prev_di_pc = self.code.items.len;
+        },
+        .plan9 => |dbg_out| {
+            if (delta_pc <= 0) return; // only do this when the pc changes
+            // we have already checked the target in the linker to make sure it is compatable
+            const quant = @import("../../link/Plan9/aout.zig").getPCQuant(self.target.cpu.arch) catch unreachable;
+
+            // increasing the line number
+            try @import("../../link/Plan9.zig").changeLine(dbg_out.dbg_line, delta_line);
+            // increasing the pc
+            const d_pc_p9 = @intCast(i64, delta_pc) - quant;
+            if (d_pc_p9 > 0) {
+                // minus one because if its the last one, we want to leave space to change the line which is one quanta
+                try dbg_out.dbg_line.append(@intCast(u8, @divExact(d_pc_p9, quant) + 128) - quant);
+                if (dbg_out.pcop_change_index.*) |pci|
+                    dbg_out.dbg_line.items[pci] += 1;
+                dbg_out.pcop_change_index.* = @intCast(u32, dbg_out.dbg_line.items.len - 1);
+            } else if (d_pc_p9 == 0) {
+                // we don't need to do anything, because adding the quant does it for us
+            } else unreachable;
+            if (dbg_out.start_line.* == null)
+                dbg_out.start_line.* = self.prev_di_line;
+            dbg_out.end_line.* = line;
+            // only do this if the pc changed
+            self.prev_di_line = line;
+            self.prev_di_column = column;
+            self.prev_di_pc = self.code.items.len;
+        },
+        .none => {},
+    }
+}
+
+/// Asserts there is already capacity to insert into top branch inst_table.
+fn processDeath(self: *Self, inst: Air.Inst.Index) void {
+    const air_tags = self.air.instructions.items(.tag);
+    if (air_tags[inst] == .constant) return; // Constants are immortal.
+    // When editing this function, note that the logic must synchronize with `reuseOperand`.
+    const prev_value = self.getResolvedInstValue(inst);
+    const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
+    branch.inst_table.putAssumeCapacity(inst, .dead);
+    switch (prev_value) {
+        .register => |reg| {
+            self.register_manager.freeReg(reg);
+        },
+        else => {}, // TODO process stack allocation death
+    }
+}
+
+/// Called when there are no operands, and the instruction is always unreferenced.
+fn finishAirBookkeeping(self: *Self) void {
+    if (std.debug.runtime_safety) {
+        self.air_bookkeeping += 1;
+    }
+}
+
+fn finishAir(self: *Self, inst: Air.Inst.Index, result: MCValue, operands: [Liveness.bpi - 1]Air.Inst.Ref) void {
+    var tomb_bits = self.liveness.getTombBits(inst);
+    for (operands) |op| {
+        const dies = @truncate(u1, tomb_bits) != 0;
+        tomb_bits >>= 1;
+        if (!dies) continue;
+        const op_int = @enumToInt(op);
+        if (op_int < Air.Inst.Ref.typed_value_map.len) continue;
+        const op_index = @intCast(Air.Inst.Index, op_int - Air.Inst.Ref.typed_value_map.len);
+        self.processDeath(op_index);
+    }
+    const is_used = @truncate(u1, tomb_bits) == 0;
+    if (is_used) {
+        log.debug("%{d} => {}", .{ inst, result });
+        const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
+        branch.inst_table.putAssumeCapacityNoClobber(inst, result);
+
+        switch (result) {
+            .register => |reg| {
+                // In some cases (such as bitcast), an operand
+                // may be the same MCValue as the result. If
+                // that operand died and was a register, it
+                // was freed by processDeath. We have to
+                // "re-allocate" the register.
+                if (self.register_manager.isRegFree(reg)) {
+                    self.register_manager.getRegAssumeFree(reg, inst);
+                }
+            },
+            else => {},
+        }
+    }
+    self.finishAirBookkeeping();
+}
+
+fn ensureProcessDeathCapacity(self: *Self, additional_count: usize) !void {
+    const table = &self.branch_stack.items[self.branch_stack.items.len - 1].inst_table;
+    try table.ensureUnusedCapacity(self.gpa, additional_count);
+}
+
+/// Adds a Type to the .debug_info at the current position. The bytes will be populated later,
+/// after codegen for this symbol is done.
+fn addDbgInfoTypeReloc(self: *Self, ty: Type) !void {
+    switch (self.debug_output) {
+        .dwarf => |dbg_out| {
+            assert(ty.hasCodeGenBits());
+            const index = dbg_out.dbg_info.items.len;
+            try dbg_out.dbg_info.resize(index + 4); // DW.AT.type,  DW.FORM.ref4
+
+            const gop = try dbg_out.dbg_info_type_relocs.getOrPut(self.gpa, ty);
+            if (!gop.found_existing) {
+                gop.value_ptr.* = .{
+                    .off = undefined,
+                    .relocs = .{},
+                };
+            }
+            try gop.value_ptr.relocs.append(self.gpa, @intCast(u32, index));
+        },
+        .plan9 => {},
+        .none => {},
+    }
+}
+
+fn allocMem(self: *Self, inst: Air.Inst.Index, abi_size: u32, abi_align: u32) !u32 {
+    if (abi_align > self.stack_align)
+        self.stack_align = abi_align;
+    // TODO find a free slot instead of always appending
+    const offset = mem.alignForwardGeneric(u32, self.next_stack_offset, abi_align);
+    self.next_stack_offset = offset + abi_size;
+    if (self.next_stack_offset > self.max_end_stack)
+        self.max_end_stack = self.next_stack_offset;
+    try self.stack.putNoClobber(self.gpa, offset, .{
+        .inst = inst,
+        .size = abi_size,
+    });
+    return offset;
+}
+
+/// Use a pointer instruction as the basis for allocating stack memory.
+fn allocMemPtr(self: *Self, inst: Air.Inst.Index) !u32 {
+    const elem_ty = self.air.typeOfIndex(inst).elemType();
+    const abi_size = math.cast(u32, elem_ty.abiSize(self.target.*)) catch {
+        return self.fail("type '{}' too big to fit into stack frame", .{elem_ty});
+    };
+    // TODO swap this for inst.ty.ptrAlign
+    const abi_align = elem_ty.abiAlignment(self.target.*);
+    return self.allocMem(inst, abi_size, abi_align);
+}
+
+fn allocRegOrMem(self: *Self, inst: Air.Inst.Index, reg_ok: bool) !MCValue {
+    const elem_ty = self.air.typeOfIndex(inst);
+    const abi_size = math.cast(u32, elem_ty.abiSize(self.target.*)) catch {
+        return self.fail("type '{}' too big to fit into stack frame", .{elem_ty});
+    };
+    const abi_align = elem_ty.abiAlignment(self.target.*);
+    if (abi_align > self.stack_align)
+        self.stack_align = abi_align;
+
+    if (reg_ok) {
+        // Make sure the type can fit in a register before we try to allocate one.
+        const ptr_bits = self.target.cpu.arch.ptrBitWidth();
+        const ptr_bytes: u64 = @divExact(ptr_bits, 8);
+        if (abi_size <= ptr_bytes) {
+            if (self.register_manager.tryAllocReg(inst, &.{})) |reg| {
+                return MCValue{ .register = reg };
+            }
+        }
+    }
+    const stack_offset = try self.allocMem(inst, abi_size, abi_align);
+    return MCValue{ .stack_offset = stack_offset };
+}
+
+pub fn spillInstruction(self: *Self, reg: Register, inst: Air.Inst.Index) !void {
+    const stack_mcv = try self.allocRegOrMem(inst, false);
+    log.debug("spilling {d} to stack mcv {any}", .{ inst, stack_mcv });
+    const reg_mcv = self.getResolvedInstValue(inst);
+    assert(reg == reg_mcv.register);
+    const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
+    try branch.inst_table.put(self.gpa, inst, stack_mcv);
+    try self.genSetStack(self.air.typeOfIndex(inst), stack_mcv.stack_offset, reg_mcv);
+}
+
+/// Copies a value to a register without tracking the register. The register is not considered
+/// allocated. A second call to `copyToTmpRegister` may return the same register.
+/// This can have a side effect of spilling instructions to the stack to free up a register.
+fn copyToTmpRegister(self: *Self, ty: Type, mcv: MCValue) !Register {
+    const reg = try self.register_manager.allocReg(null, &.{});
+    try self.genSetReg(ty, reg, mcv);
+    return reg;
+}
+
+/// Allocates a new register and copies `mcv` into it.
+/// `reg_owner` is the instruction that gets associated with the register in the register table.
+/// This can have a side effect of spilling instructions to the stack to free up a register.
+fn copyToNewRegister(self: *Self, reg_owner: Air.Inst.Index, mcv: MCValue) !MCValue {
+    const reg = try self.register_manager.allocReg(reg_owner, &.{});
+    try self.genSetReg(self.air.typeOfIndex(reg_owner), reg, mcv);
+    return MCValue{ .register = reg };
+}
+
+fn airAlloc(self: *Self, inst: Air.Inst.Index) !void {
+    const stack_offset = try self.allocMemPtr(inst);
+    return self.finishAir(inst, .{ .ptr_stack_offset = stack_offset }, .{ .none, .none, .none });
+}
+
+fn airRetPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const stack_offset = try self.allocMemPtr(inst);
+    return self.finishAir(inst, .{ .ptr_stack_offset = stack_offset }, .{ .none, .none, .none });
+}
+
+fn airFptrunc(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airFptrunc for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airFpext(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airFpext for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airIntCast(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    if (self.liveness.isUnused(inst))
+        return self.finishAir(inst, .dead, .{ ty_op.operand, .none, .none });
+
+    const operand_ty = self.air.typeOf(ty_op.operand);
+    const operand = try self.resolveInst(ty_op.operand);
+    const info_a = operand_ty.intInfo(self.target.*);
+    const info_b = self.air.typeOfIndex(inst).intInfo(self.target.*);
+    if (info_a.signedness != info_b.signedness)
+        return self.fail("TODO gen intcast sign safety in semantic analysis", .{});
+
+    if (info_a.bits == info_b.bits)
+        return self.finishAir(inst, operand, .{ ty_op.operand, .none, .none });
+
+    return self.fail("TODO implement intCast for {}", .{self.target.cpu.arch});
+    // return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airTrunc(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    if (self.liveness.isUnused(inst))
+        return self.finishAir(inst, .dead, .{ ty_op.operand, .none, .none });
+
+    const operand = try self.resolveInst(ty_op.operand);
+    _ = operand;
+    return self.fail("TODO implement trunc for {}", .{self.target.cpu.arch});
+    // return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airBoolToInt(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const operand = try self.resolveInst(un_op);
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else operand;
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airNot(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand = try self.resolveInst(ty_op.operand);
+        switch (operand) {
+            .dead => unreachable,
+            .unreach => unreachable,
+            .compare_flags_unsigned => |op| {
+                const r = MCValue{
+                    .compare_flags_unsigned = switch (op) {
+                        .gte => .lt,
+                        .gt => .lte,
+                        .neq => .eq,
+                        .lt => .gte,
+                        .lte => .gt,
+                        .eq => .neq,
+                    },
+                };
+                break :result r;
+            },
+            .compare_flags_signed => |op| {
+                const r = MCValue{
+                    .compare_flags_signed = switch (op) {
+                        .gte => .lt,
+                        .gt => .lte,
+                        .neq => .eq,
+                        .lt => .gte,
+                        .lte => .gt,
+                        .eq => .neq,
+                    },
+                };
+                break :result r;
+            },
+            else => {},
+        }
+
+        return self.fail("TODO implement NOT for {}", .{self.target.cpu.arch});
+    };
+
+    _ = result;
+    // return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airMin(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement min for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airMax(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement max for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airSlice(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const bin_op = self.air.extraData(Air.Bin, ty_pl.payload).data;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airAdd(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement add for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airAddWrap(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement addwrap for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airAddSat(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement add_sat for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airSub(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement sub for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airSubWrap(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement subwrap for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airSubSat(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement sub_sat for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airMul(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mul for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airMulWrap(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mulwrap for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airMulSat(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mul_sat for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airDiv(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement div for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airRem(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement rem for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airMod(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mod for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airBitAnd(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement bitwise and for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airBitOr(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement bitwise or for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airXor(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement xor for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airShl(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement shl for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airShlSat(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement shl_sat for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airShr(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement shr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airOptionalPayload(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement .optional_payload for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airOptionalPayloadPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement .optional_payload_ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airUnwrapErrErr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union error for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airUnwrapErrPayload(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union payload for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+// *(E!T) -> E
+fn airUnwrapErrErrPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union error ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+// *(E!T) -> *T
+fn airUnwrapErrPayloadPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union payload ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airWrapOptional(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const optional_ty = self.air.typeOfIndex(inst);
+
+        // Optional with a zero-bit payload type is just a boolean true
+        if (optional_ty.abiSize(self.target.*) == 1)
+            break :result MCValue{ .immediate = 1 };
+
+        return self.fail("TODO implement wrap optional for {}", .{self.target.cpu.arch});
+    };
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+/// T to E!T
+fn airWrapErrUnionPayload(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement wrap errunion payload for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+/// E to E!T
+fn airWrapErrUnionErr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement wrap errunion error for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airSlicePtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airSliceLen(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_len for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airPtrSliceLenPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_slice_len_ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airPtrSlicePtrPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_slice_ptr_ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airSliceElemVal(self: *Self, inst: Air.Inst.Index) !void {
+    const is_volatile = false; // TODO
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (!is_volatile and self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_elem_val for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airSliceElemPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const extra = self.air.extraData(Air.Bin, ty_pl.payload).data;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_elem_ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ extra.lhs, extra.rhs, .none });
+}
+
+fn airArrayElemVal(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement array_elem_val for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airPtrElemVal(self: *Self, inst: Air.Inst.Index) !void {
+    const is_volatile = false; // TODO
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const result: MCValue = if (!is_volatile and self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_elem_val for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airPtrElemPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const extra = self.air.extraData(Air.Bin, ty_pl.payload).data;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_elem_ptr for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ extra.lhs, extra.rhs, .none });
+}
+
+fn airSetUnionTag(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    _ = bin_op;
+    return self.fail("TODO implement airSetUnionTag for {}", .{self.target.cpu.arch});
+    // return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airGetUnionTag(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airGetUnionTag for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airClz(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airClz for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airCtz(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airCtz for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airPopcount(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airPopcount for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn reuseOperand(self: *Self, inst: Air.Inst.Index, operand: Air.Inst.Ref, op_index: Liveness.OperandInt, mcv: MCValue) bool {
+    if (!self.liveness.operandDies(inst, op_index))
+        return false;
+
+    switch (mcv) {
+        .register => |reg| {
+            // If it's in the registers table, need to associate the register with the
+            // new instruction.
+            if (reg.allocIndex()) |index| {
+                if (!self.register_manager.isRegFree(reg)) {
+                    self.register_manager.registers[index] = inst;
+                }
+            }
+            log.debug("%{d} => {} (reused)", .{ inst, reg });
+        },
+        .stack_offset => |off| {
+            log.debug("%{d} => stack offset {d} (reused)", .{ inst, off });
+        },
+        else => return false,
+    }
+
+    // Prevent the operand deaths processing code from deallocating it.
+    self.liveness.clearOperandDeath(inst, op_index);
+
+    // That makes us responsible for doing the rest of the stuff that processDeath would have done.
+    const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
+    branch.inst_table.putAssumeCapacity(Air.refToIndex(operand).?, .dead);
+
+    return true;
+}
+
+fn load(self: *Self, dst_mcv: MCValue, ptr: MCValue, ptr_ty: Type) InnerError!void {
+    const elem_ty = ptr_ty.elemType();
+    switch (ptr) {
+        .none => unreachable,
+        .undef => unreachable,
+        .unreach => unreachable,
+        .dead => unreachable,
+        .compare_flags_unsigned => unreachable,
+        .compare_flags_signed => unreachable,
+        .immediate => |imm| try self.setRegOrMem(elem_ty, dst_mcv, .{ .memory = imm }),
+        .ptr_stack_offset => |off| try self.setRegOrMem(elem_ty, dst_mcv, .{ .stack_offset = off }),
+        .ptr_embedded_in_code => |off| {
+            try self.setRegOrMem(elem_ty, dst_mcv, .{ .embedded_in_code = off });
+        },
+        .embedded_in_code => {
+            return self.fail("TODO implement loading from MCValue.embedded_in_code", .{});
+        },
+        .register => {
+            return self.fail("TODO implement loading from MCValue.register", .{});
+        },
+        .memory => |addr| {
+            const reg = try self.register_manager.allocReg(null, &.{});
+            try self.genSetReg(ptr_ty, reg, .{ .memory = addr });
+            try self.load(dst_mcv, .{ .register = reg }, ptr_ty);
+        },
+        .stack_offset => {
+            return self.fail("TODO implement loading from MCValue.stack_offset", .{});
+        },
+    }
+}
+
+fn airLoad(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const elem_ty = self.air.typeOfIndex(inst);
+    const result: MCValue = result: {
+        if (!elem_ty.hasCodeGenBits())
+            break :result MCValue.none;
+
+        const ptr = try self.resolveInst(ty_op.operand);
+        const is_volatile = self.air.typeOf(ty_op.operand).isVolatilePtr();
+        if (self.liveness.isUnused(inst) and !is_volatile)
+            break :result MCValue.dead;
+
+        const dst_mcv: MCValue = blk: {
+            if (self.reuseOperand(inst, ty_op.operand, 0, ptr)) {
+                // The MCValue that holds the pointer can be re-used as the value.
+                break :blk ptr;
+            } else {
+                break :blk try self.allocRegOrMem(inst, true);
+            }
+        };
+        try self.load(dst_mcv, ptr, self.air.typeOf(ty_op.operand));
+        break :result dst_mcv;
+    };
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airStore(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const ptr = try self.resolveInst(bin_op.lhs);
+    const value = try self.resolveInst(bin_op.rhs);
+    const elem_ty = self.air.typeOf(bin_op.rhs);
+    switch (ptr) {
+        .none => unreachable,
+        .undef => unreachable,
+        .unreach => unreachable,
+        .dead => unreachable,
+        .compare_flags_unsigned => unreachable,
+        .compare_flags_signed => unreachable,
+        .immediate => |imm| {
+            try self.setRegOrMem(elem_ty, .{ .memory = imm }, value);
+        },
+        .ptr_stack_offset => |off| {
+            try self.genSetStack(elem_ty, off, value);
+        },
+        .ptr_embedded_in_code => |off| {
+            try self.setRegOrMem(elem_ty, .{ .embedded_in_code = off }, value);
+        },
+        .embedded_in_code => {
+            return self.fail("TODO implement storing to MCValue.embedded_in_code", .{});
+        },
+        .register => {
+            return self.fail("TODO implement storing to MCValue.register", .{});
+        },
+        .memory => {
+            return self.fail("TODO implement storing to MCValue.memory", .{});
+        },
+        .stack_offset => {
+            return self.fail("TODO implement storing to MCValue.stack_offset", .{});
+        },
+    }
+    return self.finishAir(inst, .dead, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airStructFieldPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const extra = self.air.extraData(Air.StructField, ty_pl.payload).data;
+    return self.structFieldPtr(extra.struct_operand, ty_pl.ty, extra.field_index);
+}
+
+fn airStructFieldPtrIndex(self: *Self, inst: Air.Inst.Index, index: u8) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    return self.structFieldPtr(ty_op.operand, ty_op.ty, index);
+}
+fn structFieldPtr(self: *Self, operand: Air.Inst.Ref, ty: Air.Inst.Ref, index: u32) !void {
+    _ = self;
+    _ = operand;
+    _ = ty;
+    _ = index;
+    return self.fail("TODO implement codegen struct_field_ptr", .{});
+    //return self.finishAir(inst, result, .{ extra.struct_ptr, .none, .none });
+}
+
+fn airStructFieldVal(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const extra = self.air.extraData(Air.StructField, ty_pl.payload).data;
+    _ = extra;
+    return self.fail("TODO implement codegen struct_field_val", .{});
+    //return self.finishAir(inst, result, .{ extra.struct_ptr, .none, .none });
+}
+
+fn genArgDbgInfo(self: *Self, inst: Air.Inst.Index, mcv: MCValue) !void {
+    const ty_str = self.air.instructions.items(.data)[inst].ty_str;
+    const zir = &self.mod_fn.owner_decl.getFileScope().zir;
+    const name = zir.nullTerminatedString(ty_str.str);
+    const name_with_null = name.ptr[0 .. name.len + 1];
+    const ty = self.air.getRefType(ty_str.ty);
+
+    switch (mcv) {
+        .register => |reg| {
+            switch (self.debug_output) {
+                .dwarf => |dbg_out| {
+                    try dbg_out.dbg_info.ensureUnusedCapacity(3);
+                    dbg_out.dbg_info.appendAssumeCapacity(link.File.Elf.abbrev_parameter);
+                    dbg_out.dbg_info.appendSliceAssumeCapacity(&[2]u8{ // DW.AT.location, DW.FORM.exprloc
+                        1, // ULEB128 dwarf expression length
+                        reg.dwarfLocOp(),
+                    });
+                    try dbg_out.dbg_info.ensureUnusedCapacity(5 + name_with_null.len);
+                    try self.addDbgInfoTypeReloc(ty); // DW.AT.type,  DW.FORM.ref4
+                    dbg_out.dbg_info.appendSliceAssumeCapacity(name_with_null); // DW.AT.name, DW.FORM.string
+                },
+                .plan9 => {},
+                .none => {},
+            }
+        },
+        .stack_offset => |offset| {
+            _ = offset;
+            switch (self.debug_output) {
+                .dwarf => {},
+                .plan9 => {},
+                .none => {},
+            }
+        },
+        else => {},
+    }
+}
+
+fn airArg(self: *Self, inst: Air.Inst.Index) !void {
+    const arg_index = self.arg_index;
+    self.arg_index += 1;
+
+    const ty = self.air.typeOfIndex(inst);
+    _ = ty;
+
+    const result = self.args[arg_index];
+    // TODO support stack-only arguments
+    // TODO Copy registers to the stack
+    const mcv = result;
+    try self.genArgDbgInfo(inst, mcv);
+
+    if (self.liveness.isUnused(inst))
+        return self.finishAirBookkeeping();
+
+    switch (mcv) {
+        .register => |reg| {
+            self.register_manager.getRegAssumeFree(reg, inst);
+        },
+        else => {},
+    }
+
+    return self.finishAir(inst, mcv, .{ .none, .none, .none });
+}
+
+fn airBreakpoint(self: *Self) !void {
+    mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.ebreak.toU32());
+    return self.finishAirBookkeeping();
+}
+
+fn airFence(self: *Self) !void {
+    return self.fail("TODO implement fence() for {}", .{self.target.cpu.arch});
+    //return self.finishAirBookkeeping();
+}
+
+fn airCall(self: *Self, inst: Air.Inst.Index) !void {
+    const pl_op = self.air.instructions.items(.data)[inst].pl_op;
+    const fn_ty = self.air.typeOf(pl_op.operand);
+    const callee = pl_op.operand;
+    const extra = self.air.extraData(Air.Call, pl_op.payload);
+    const args = @bitCast([]const Air.Inst.Ref, self.air.extra[extra.end..][0..extra.data.args_len]);
+
+    var info = try self.resolveCallingConventionValues(fn_ty);
+    defer info.deinit(self);
+
+    // Due to incremental compilation, how function calls are generated depends
+    // on linking.
+    if (self.bin_file.tag == link.File.Elf.base_tag or self.bin_file.tag == link.File.Coff.base_tag) {
+        if (info.args.len > 0) return self.fail("TODO implement fn args for {}", .{self.target.cpu.arch});
+
+        if (self.air.value(callee)) |func_value| {
+            if (func_value.castTag(.function)) |func_payload| {
+                const func = func_payload.data;
+
+                const ptr_bits = self.target.cpu.arch.ptrBitWidth();
+                const ptr_bytes: u64 = @divExact(ptr_bits, 8);
+                const got_addr = if (self.bin_file.cast(link.File.Elf)) |elf_file| blk: {
+                    const got = &elf_file.program_headers.items[elf_file.phdr_got_index.?];
+                    break :blk @intCast(u32, got.p_vaddr + func.owner_decl.link.elf.offset_table_index * ptr_bytes);
+                } else if (self.bin_file.cast(link.File.Coff)) |coff_file|
+                    coff_file.offset_table_virtual_address + func.owner_decl.link.coff.offset_table_index * ptr_bytes
+                else
+                    unreachable;
+
+                try self.genSetReg(Type.initTag(.usize), .ra, .{ .memory = got_addr });
+                mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.jalr(.ra, 0, .ra).toU32());
+            } else if (func_value.castTag(.extern_fn)) |_| {
+                return self.fail("TODO implement calling extern functions", .{});
+            } else {
+                return self.fail("TODO implement calling bitcasted functions", .{});
+            }
+        } else {
+            return self.fail("TODO implement calling runtime known function pointer", .{});
+        }
+    } else if (self.bin_file.cast(link.File.MachO)) |_| {
+        unreachable; // unsupported architecture for MachO
+    } else if (self.bin_file.cast(link.File.Plan9)) |_| {
+        return self.fail("TODO implement call on plan9 for {}", .{self.target.cpu.arch});
+    } else unreachable;
+
+    const result: MCValue = result: {
+        switch (info.return_value) {
+            .register => |reg| {
+                if (Register.allocIndex(reg) == null) {
+                    // Save function return value in a callee saved register
+                    break :result try self.copyToNewRegister(inst, info.return_value);
+                }
+            },
+            else => {},
+        }
+        break :result info.return_value;
+    };
+
+    if (args.len <= Liveness.bpi - 2) {
+        var buf = [1]Air.Inst.Ref{.none} ** (Liveness.bpi - 1);
+        buf[0] = callee;
+        std.mem.copy(Air.Inst.Ref, buf[1..], args);
+        return self.finishAir(inst, result, buf);
+    }
+    var bt = try self.iterateBigTomb(inst, 1 + args.len);
+    bt.feed(callee);
+    for (args) |arg| {
+        bt.feed(arg);
+    }
+    return bt.finishAir(result);
+}
+
+fn ret(self: *Self, mcv: MCValue) !void {
+    const ret_ty = self.fn_type.fnReturnType();
+    try self.setRegOrMem(ret_ty, self.ret_mcv, mcv);
+    mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.jalr(.zero, 0, .ra).toU32());
+}
+
+fn airRet(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const operand = try self.resolveInst(un_op);
+    try self.ret(operand);
+    return self.finishAir(inst, .dead, .{ un_op, .none, .none });
+}
+
+fn airRetLoad(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const ptr = try self.resolveInst(un_op);
+    _ = ptr;
+    return self.fail("TODO implement airRetLoad for {}", .{self.target.cpu.arch});
+    //return self.finishAir(inst, .dead, .{ un_op, .none, .none });
+}
+
+fn airCmp(self: *Self, inst: Air.Inst.Index, op: math.CompareOperator) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    if (self.liveness.isUnused(inst))
+        return self.finishAir(inst, .dead, .{ bin_op.lhs, bin_op.rhs, .none });
+    const ty = self.air.typeOf(bin_op.lhs);
+    assert(ty.eql(self.air.typeOf(bin_op.rhs)));
+    if (ty.zigTypeTag() == .ErrorSet)
+        return self.fail("TODO implement cmp for errors", .{});
+
+    const lhs = try self.resolveInst(bin_op.lhs);
+    const rhs = try self.resolveInst(bin_op.rhs);
+    _ = op;
+    _ = lhs;
+    _ = rhs;
+
+    return self.fail("TODO implement cmp for {}", .{self.target.cpu.arch});
+    // return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn airDbgStmt(self: *Self, inst: Air.Inst.Index) !void {
+    const dbg_stmt = self.air.instructions.items(.data)[inst].dbg_stmt;
+    try self.dbgAdvancePCAndLine(dbg_stmt.line, dbg_stmt.column);
+    return self.finishAirBookkeeping();
+}
+
+fn airCondBr(self: *Self, inst: Air.Inst.Index) !void {
+    _ = inst;
+
+    return self.fail("TODO implement condbr {}", .{self.target.cpu.arch});
+    // return self.finishAir(inst, .unreach, .{ pl_op.operand, .none, .none });
+}
+
+fn isNull(self: *Self, operand: MCValue) !MCValue {
+    _ = operand;
+    // Here you can specialize this instruction if it makes sense to, otherwise the default
+    // will call isNonNull and invert the result.
+    return self.fail("TODO call isNonNull and invert the result", .{});
+}
+
+fn isNonNull(self: *Self, operand: MCValue) !MCValue {
+    _ = operand;
+    // Here you can specialize this instruction if it makes sense to, otherwise the default
+    // will call isNull and invert the result.
+    return self.fail("TODO call isNull and invert the result", .{});
+}
+
+fn isErr(self: *Self, operand: MCValue) !MCValue {
+    _ = operand;
+    // Here you can specialize this instruction if it makes sense to, otherwise the default
+    // will call isNonNull and invert the result.
+    return self.fail("TODO call isNonErr and invert the result", .{});
+}
+
+fn isNonErr(self: *Self, operand: MCValue) !MCValue {
+    _ = operand;
+    // Here you can specialize this instruction if it makes sense to, otherwise the default
+    // will call isNull and invert the result.
+    return self.fail("TODO call isErr and invert the result", .{});
+}
+
+fn airIsNull(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand = try self.resolveInst(un_op);
+        break :result try self.isNull(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airIsNullPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand_ptr = try self.resolveInst(un_op);
+        const operand: MCValue = blk: {
+            if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
+                // The MCValue that holds the pointer can be re-used as the value.
+                break :blk operand_ptr;
+            } else {
+                break :blk try self.allocRegOrMem(inst, true);
+            }
+        };
+        try self.load(operand, operand_ptr, self.air.typeOf(un_op));
+        break :result try self.isNull(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airIsNonNull(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand = try self.resolveInst(un_op);
+        break :result try self.isNonNull(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airIsNonNullPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand_ptr = try self.resolveInst(un_op);
+        const operand: MCValue = blk: {
+            if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
+                // The MCValue that holds the pointer can be re-used as the value.
+                break :blk operand_ptr;
+            } else {
+                break :blk try self.allocRegOrMem(inst, true);
+            }
+        };
+        try self.load(operand, operand_ptr, self.air.typeOf(un_op));
+        break :result try self.isNonNull(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airIsErr(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand = try self.resolveInst(un_op);
+        break :result try self.isErr(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airIsErrPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand_ptr = try self.resolveInst(un_op);
+        const operand: MCValue = blk: {
+            if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
+                // The MCValue that holds the pointer can be re-used as the value.
+                break :blk operand_ptr;
+            } else {
+                break :blk try self.allocRegOrMem(inst, true);
+            }
+        };
+        try self.load(operand, operand_ptr, self.air.typeOf(un_op));
+        break :result try self.isErr(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airIsNonErr(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand = try self.resolveInst(un_op);
+        break :result try self.isNonErr(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airIsNonErrPtr(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const operand_ptr = try self.resolveInst(un_op);
+        const operand: MCValue = blk: {
+            if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
+                // The MCValue that holds the pointer can be re-used as the value.
+                break :blk operand_ptr;
+            } else {
+                break :blk try self.allocRegOrMem(inst, true);
+            }
+        };
+        try self.load(operand, operand_ptr, self.air.typeOf(un_op));
+        break :result try self.isNonErr(operand);
+    };
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airLoop(self: *Self, inst: Air.Inst.Index) !void {
+    // A loop is a setup to be able to jump back to the beginning.
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const loop = self.air.extraData(Air.Block, ty_pl.payload);
+    const body = self.air.extra[loop.end..][0..loop.data.body_len];
+    const start_index = self.code.items.len;
+    try self.genBody(body);
+    try self.jump(start_index);
+    return self.finishAirBookkeeping();
+}
+
+/// Send control flow to the `index` of `self.code`.
+fn jump(self: *Self, index: usize) !void {
+    _ = index;
+    return self.fail("TODO implement jump for {}", .{self.target.cpu.arch});
+}
+
+fn airBlock(self: *Self, inst: Air.Inst.Index) !void {
+    try self.blocks.putNoClobber(self.gpa, inst, .{
+        // A block is a setup to be able to jump to the end.
+        .relocs = .{},
+        // It also acts as a receptacle for break operands.
+        // Here we use `MCValue.none` to represent a null value so that the first
+        // break instruction will choose a MCValue for the block result and overwrite
+        // this field. Following break instructions will use that MCValue to put their
+        // block results.
+        .mcv = MCValue{ .none = {} },
+    });
+    const block_data = self.blocks.getPtr(inst).?;
+    defer block_data.relocs.deinit(self.gpa);
+
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const extra = self.air.extraData(Air.Block, ty_pl.payload);
+    const body = self.air.extra[extra.end..][0..extra.data.body_len];
+    try self.genBody(body);
+
+    for (block_data.relocs.items) |reloc| try self.performReloc(reloc);
+
+    const result = @bitCast(MCValue, block_data.mcv);
+    return self.finishAir(inst, result, .{ .none, .none, .none });
+}
+
+fn airSwitch(self: *Self, inst: Air.Inst.Index) !void {
+    const pl_op = self.air.instructions.items(.data)[inst].pl_op;
+    const condition = pl_op.operand;
+    _ = condition;
+    return self.fail("TODO airSwitch for {}", .{self.target.cpu.arch});
+    // return self.finishAir(inst, .dead, .{ condition, .none, .none });
+}
+
+fn performReloc(self: *Self, reloc: Reloc) !void {
+    _ = self;
+    switch (reloc) {
+        .rel32 => unreachable,
+        .arm_branch => unreachable,
+    }
+}
+
+fn airBr(self: *Self, inst: Air.Inst.Index) !void {
+    const branch = self.air.instructions.items(.data)[inst].br;
+    try self.br(branch.block_inst, branch.operand);
+    return self.finishAir(inst, .dead, .{ branch.operand, .none, .none });
+}
+
+fn airBoolOp(self: *Self, inst: Air.Inst.Index) !void {
+    const bin_op = self.air.instructions.items(.data)[inst].bin_op;
+    const air_tags = self.air.instructions.items(.tag);
+    _ = air_tags;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement boolean operations for {}", .{self.target.cpu.arch});
+    return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
+}
+
+fn br(self: *Self, block: Air.Inst.Index, operand: Air.Inst.Ref) !void {
+    const block_data = self.blocks.getPtr(block).?;
+
+    if (self.air.typeOf(operand).hasCodeGenBits()) {
+        const operand_mcv = try self.resolveInst(operand);
+        const block_mcv = block_data.mcv;
+        if (block_mcv == .none) {
+            block_data.mcv = operand_mcv;
+        } else {
+            try self.setRegOrMem(self.air.typeOfIndex(block), block_mcv, operand_mcv);
+        }
+    }
+    return self.brVoid(block);
+}
+
+fn brVoid(self: *Self, block: Air.Inst.Index) !void {
+    const block_data = self.blocks.getPtr(block).?;
+
+    // Emit a jump with a relocation. It will be patched up after the block ends.
+    try block_data.relocs.ensureUnusedCapacity(self.gpa, 1);
+
+    return self.fail("TODO implement brvoid for {}", .{self.target.cpu.arch});
+}
+
+fn airAsm(self: *Self, inst: Air.Inst.Index) !void {
+    const air_datas = self.air.instructions.items(.data);
+    const air_extra = self.air.extraData(Air.Asm, air_datas[inst].ty_pl.payload);
+    const zir = self.mod_fn.owner_decl.getFileScope().zir;
+    const extended = zir.instructions.items(.data)[air_extra.data.zir_index].extended;
+    const zir_extra = zir.extraData(Zir.Inst.Asm, extended.operand);
+    const asm_source = zir.nullTerminatedString(zir_extra.data.asm_source);
+    const outputs_len = @truncate(u5, extended.small);
+    const args_len = @truncate(u5, extended.small >> 5);
+    const clobbers_len = @truncate(u5, extended.small >> 10);
+    _ = clobbers_len; // TODO honor these
+    const is_volatile = @truncate(u1, extended.small >> 15) != 0;
+    const outputs = @bitCast([]const Air.Inst.Ref, self.air.extra[air_extra.end..][0..outputs_len]);
+    const args = @bitCast([]const Air.Inst.Ref, self.air.extra[air_extra.end + outputs.len ..][0..args_len]);
+
+    if (outputs_len > 1) {
+        return self.fail("TODO implement codegen for asm with more than 1 output", .{});
+    }
+    var extra_i: usize = zir_extra.end;
+    const output_constraint: ?[]const u8 = out: {
+        var i: usize = 0;
+        while (i < outputs_len) : (i += 1) {
+            const output = zir.extraData(Zir.Inst.Asm.Output, extra_i);
+            extra_i = output.end;
+            break :out zir.nullTerminatedString(output.data.constraint);
+        }
+        break :out null;
+    };
+
+    const dead = !is_volatile and self.liveness.isUnused(inst);
+    const result: MCValue = if (dead) .dead else result: {
+        for (args) |arg| {
+            const input = zir.extraData(Zir.Inst.Asm.Input, extra_i);
+            extra_i = input.end;
+            const constraint = zir.nullTerminatedString(input.data.constraint);
+
+            if (constraint.len < 3 or constraint[0] != '{' or constraint[constraint.len - 1] != '}') {
+                return self.fail("unrecognized asm input constraint: '{s}'", .{constraint});
+            }
+            const reg_name = constraint[1 .. constraint.len - 1];
+            const reg = parseRegName(reg_name) orelse
+                return self.fail("unrecognized register: '{s}'", .{reg_name});
+
+            const arg_mcv = try self.resolveInst(arg);
+            try self.register_manager.getReg(reg, null);
+            try self.genSetReg(self.air.typeOf(arg), reg, arg_mcv);
+        }
+
+        if (mem.eql(u8, asm_source, "ecall")) {
+            mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.ecall.toU32());
+        } else {
+            return self.fail("TODO implement support for more riscv64 assembly instructions", .{});
+        }
+
+        if (output_constraint) |output| {
+            if (output.len < 4 or output[0] != '=' or output[1] != '{' or output[output.len - 1] != '}') {
+                return self.fail("unrecognized asm output constraint: '{s}'", .{output});
+            }
+            const reg_name = output[2 .. output.len - 1];
+            const reg = parseRegName(reg_name) orelse
+                return self.fail("unrecognized register: '{s}'", .{reg_name});
+            break :result MCValue{ .register = reg };
+        } else {
+            break :result MCValue{ .none = {} };
+        }
+    };
+    if (outputs.len + args.len <= Liveness.bpi - 1) {
+        var buf = [1]Air.Inst.Ref{.none} ** (Liveness.bpi - 1);
+        std.mem.copy(Air.Inst.Ref, &buf, outputs);
+        std.mem.copy(Air.Inst.Ref, buf[outputs.len..], args);
+        return self.finishAir(inst, result, buf);
+    }
+    var bt = try self.iterateBigTomb(inst, outputs.len + args.len);
+    for (outputs) |output| {
+        bt.feed(output);
+    }
+    for (args) |arg| {
+        bt.feed(arg);
+    }
+    return bt.finishAir(result);
+}
+
+fn iterateBigTomb(self: *Self, inst: Air.Inst.Index, operand_count: usize) !BigTomb {
+    try self.ensureProcessDeathCapacity(operand_count + 1);
+    return BigTomb{
+        .function = self,
+        .inst = inst,
+        .tomb_bits = self.liveness.getTombBits(inst),
+        .big_tomb_bits = self.liveness.special.get(inst) orelse 0,
+        .bit_index = 0,
+    };
+}
+
+/// Sets the value without any modifications to register allocation metadata or stack allocation metadata.
+fn setRegOrMem(self: *Self, ty: Type, loc: MCValue, val: MCValue) !void {
+    switch (loc) {
+        .none => return,
+        .register => |reg| return self.genSetReg(ty, reg, val),
+        .stack_offset => |off| return self.genSetStack(ty, off, val),
+        .memory => {
+            return self.fail("TODO implement setRegOrMem for memory", .{});
+        },
+        else => unreachable,
+    }
+}
+
+fn genSetStack(self: *Self, ty: Type, stack_offset: u32, mcv: MCValue) InnerError!void {
+    _ = ty;
+    _ = stack_offset;
+    _ = mcv;
+    return self.fail("TODO implement getSetStack for {}", .{self.target.cpu.arch});
+}
+
+fn genSetReg(self: *Self, ty: Type, reg: Register, mcv: MCValue) InnerError!void {
+    switch (mcv) {
+        .dead => unreachable,
+        .ptr_stack_offset => unreachable,
+        .ptr_embedded_in_code => unreachable,
+        .unreach, .none => return, // Nothing to do.
+        .undef => {
+            if (!self.wantSafety())
+                return; // The already existing value will do just fine.
+            // Write the debug undefined value.
+            return self.genSetReg(ty, reg, .{ .immediate = 0xaaaaaaaaaaaaaaaa });
+        },
+        .immediate => |unsigned_x| {
+            const x = @bitCast(i64, unsigned_x);
+            if (math.minInt(i12) <= x and x <= math.maxInt(i12)) {
+                mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.addi(reg, .zero, @truncate(i12, x)).toU32());
+                return;
+            }
+            if (math.minInt(i32) <= x and x <= math.maxInt(i32)) {
+                const lo12 = @truncate(i12, x);
+                const carry: i32 = if (lo12 < 0) 1 else 0;
+                const hi20 = @truncate(i20, (x >> 12) +% carry);
+
+                // TODO: add test case for 32-bit immediate
+                mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.lui(reg, hi20).toU32());
+                mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.addi(reg, reg, lo12).toU32());
+                return;
+            }
+            // li rd, immediate
+            // "Myriad sequences"
+            return self.fail("TODO genSetReg 33-64 bit immediates for riscv64", .{}); // glhf
+        },
+        .memory => |addr| {
+            // The value is in memory at a hard-coded address.
+            // If the type is a pointer, it means the pointer address is at this memory location.
+            try self.genSetReg(ty, reg, .{ .immediate = addr });
+
+            mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.ld(reg, 0, reg).toU32());
+            // LOAD imm=[i12 offset = 0], rs1 =
+
+            // return self.fail("TODO implement genSetReg memory for riscv64");
+        },
+        else => return self.fail("TODO implement getSetReg for riscv64 {}", .{mcv}),
+    }
+}
+
+fn airPtrToInt(self: *Self, inst: Air.Inst.Index) !void {
+    const un_op = self.air.instructions.items(.data)[inst].un_op;
+    const result = try self.resolveInst(un_op);
+    return self.finishAir(inst, result, .{ un_op, .none, .none });
+}
+
+fn airBitCast(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result = try self.resolveInst(ty_op.operand);
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airArrayToSlice(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airArrayToSlice for {}", .{
+        self.target.cpu.arch,
+    });
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airIntToFloat(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airIntToFloat for {}", .{
+        self.target.cpu.arch,
+    });
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airFloatToInt(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airFloatToInt for {}", .{
+        self.target.cpu.arch,
+    });
+    return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
+}
+
+fn airCmpxchg(self: *Self, inst: Air.Inst.Index) !void {
+    const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
+    const extra = self.air.extraData(Air.Block, ty_pl.payload);
+    _ = extra;
+    return self.fail("TODO implement airCmpxchg for {}", .{
+        self.target.cpu.arch,
+    });
+    // return self.finishAir(inst, result, .{ extra.ptr, extra.expected_value, extra.new_value });
+}
+
+fn airAtomicRmw(self: *Self, inst: Air.Inst.Index) !void {
+    _ = inst;
+    return self.fail("TODO implement airCmpxchg for {}", .{self.target.cpu.arch});
+}
+
+fn airAtomicLoad(self: *Self, inst: Air.Inst.Index) !void {
+    _ = inst;
+    return self.fail("TODO implement airAtomicLoad for {}", .{self.target.cpu.arch});
+}
+
+fn airAtomicStore(self: *Self, inst: Air.Inst.Index, order: std.builtin.AtomicOrder) !void {
+    _ = inst;
+    _ = order;
+    return self.fail("TODO implement airAtomicStore for {}", .{self.target.cpu.arch});
+}
+
+fn airMemset(self: *Self, inst: Air.Inst.Index) !void {
+    _ = inst;
+    return self.fail("TODO implement airMemset for {}", .{self.target.cpu.arch});
+}
+
+fn airMemcpy(self: *Self, inst: Air.Inst.Index) !void {
+    _ = inst;
+    return self.fail("TODO implement airMemcpy for {}", .{self.target.cpu.arch});
+}
+
+fn resolveInst(self: *Self, inst: Air.Inst.Ref) InnerError!MCValue {
+    // First section of indexes correspond to a set number of constant values.
+    const ref_int = @enumToInt(inst);
+    if (ref_int < Air.Inst.Ref.typed_value_map.len) {
+        const tv = Air.Inst.Ref.typed_value_map[ref_int];
+        if (!tv.ty.hasCodeGenBits()) {
+            return MCValue{ .none = {} };
+        }
+        return self.genTypedValue(tv);
+    }
+
+    // If the type has no codegen bits, no need to store it.
+    const inst_ty = self.air.typeOf(inst);
+    if (!inst_ty.hasCodeGenBits())
+        return MCValue{ .none = {} };
+
+    const inst_index = @intCast(Air.Inst.Index, ref_int - Air.Inst.Ref.typed_value_map.len);
+    switch (self.air.instructions.items(.tag)[inst_index]) {
+        .constant => {
+            // Constants have static lifetimes, so they are always memoized in the outer most table.
+            const branch = &self.branch_stack.items[0];
+            const gop = try branch.inst_table.getOrPut(self.gpa, inst_index);
+            if (!gop.found_existing) {
+                const ty_pl = self.air.instructions.items(.data)[inst_index].ty_pl;
+                gop.value_ptr.* = try self.genTypedValue(.{
+                    .ty = inst_ty,
+                    .val = self.air.values[ty_pl.payload],
+                });
+            }
+            return gop.value_ptr.*;
+        },
+        .const_ty => unreachable,
+        else => return self.getResolvedInstValue(inst_index),
+    }
+}
+
+fn getResolvedInstValue(self: *Self, inst: Air.Inst.Index) MCValue {
+    // Treat each stack item as a "layer" on top of the previous one.
+    var i: usize = self.branch_stack.items.len;
+    while (true) {
+        i -= 1;
+        if (self.branch_stack.items[i].inst_table.get(inst)) |mcv| {
+            assert(mcv != .dead);
+            return mcv;
+        }
+    }
+}
+
+/// If the MCValue is an immediate, and it does not fit within this type,
+/// we put it in a register.
+/// A potential opportunity for future optimization here would be keeping track
+/// of the fact that the instruction is available both as an immediate
+/// and as a register.
+fn limitImmediateType(self: *Self, operand: Air.Inst.Ref, comptime T: type) !MCValue {
+    const mcv = try self.resolveInst(operand);
+    const ti = @typeInfo(T).Int;
+    switch (mcv) {
+        .immediate => |imm| {
+            // This immediate is unsigned.
+            const U = std.meta.Int(.unsigned, ti.bits - @boolToInt(ti.signedness == .signed));
+            if (imm >= math.maxInt(U)) {
+                return MCValue{ .register = try self.copyToTmpRegister(Type.initTag(.usize), mcv) };
+            }
+        },
+        else => {},
+    }
+    return mcv;
+}
+
+fn genTypedValue(self: *Self, typed_value: TypedValue) InnerError!MCValue {
+    if (typed_value.val.isUndef())
+        return MCValue{ .undef = {} };
+    const ptr_bits = self.target.cpu.arch.ptrBitWidth();
+    const ptr_bytes: u64 = @divExact(ptr_bits, 8);
+    switch (typed_value.ty.zigTypeTag()) {
+        .Pointer => switch (typed_value.ty.ptrSize()) {
+            .Slice => {
+                var buf: Type.SlicePtrFieldTypeBuffer = undefined;
+                const ptr_type = typed_value.ty.slicePtrFieldType(&buf);
+                const ptr_mcv = try self.genTypedValue(.{ .ty = ptr_type, .val = typed_value.val });
+                const slice_len = typed_value.val.sliceLen();
+                // Codegen can't handle some kinds of indirection. If the wrong union field is accessed here it may mean
+                // the Sema code needs to use anonymous Decls or alloca instructions to store data.
+                const ptr_imm = ptr_mcv.memory;
+                _ = slice_len;
+                _ = ptr_imm;
+                // We need more general support for const data being stored in memory to make this work.
+                return self.fail("TODO codegen for const slices", .{});
+            },
+            else => {
+                if (typed_value.val.castTag(.decl_ref)) |payload| {
+                    const decl = payload.data;
+                    decl.alive = true;
+                    if (self.bin_file.cast(link.File.Elf)) |elf_file| {
+                        const got = &elf_file.program_headers.items[elf_file.phdr_got_index.?];
+                        const got_addr = got.p_vaddr + decl.link.elf.offset_table_index * ptr_bytes;
+                        return MCValue{ .memory = got_addr };
+                    } else if (self.bin_file.cast(link.File.MachO)) |_| {
+                        // TODO I'm hacking my way through here by repurposing .memory for storing
+                        // index to the GOT target symbol index.
+                        return MCValue{ .memory = decl.link.macho.local_sym_index };
+                    } else if (self.bin_file.cast(link.File.Coff)) |coff_file| {
+                        const got_addr = coff_file.offset_table_virtual_address + decl.link.coff.offset_table_index * ptr_bytes;
+                        return MCValue{ .memory = got_addr };
+                    } else if (self.bin_file.cast(link.File.Plan9)) |p9| {
+                        try p9.seeDecl(decl);
+                        const got_addr = p9.bases.data + decl.link.plan9.got_index.? * ptr_bytes;
+                        return MCValue{ .memory = got_addr };
+                    } else {
+                        return self.fail("TODO codegen non-ELF const Decl pointer", .{});
+                    }
+                }
+                if (typed_value.val.tag() == .int_u64) {
+                    return MCValue{ .immediate = typed_value.val.toUnsignedInt() };
+                }
+                return self.fail("TODO codegen more kinds of const pointers", .{});
+            },
+        },
+        .Int => {
+            const info = typed_value.ty.intInfo(self.target.*);
+            if (info.bits > ptr_bits or info.signedness == .signed) {
+                return self.fail("TODO const int bigger than ptr and signed int", .{});
+            }
+            return MCValue{ .immediate = typed_value.val.toUnsignedInt() };
+        },
+        .Bool => {
+            return MCValue{ .immediate = @boolToInt(typed_value.val.toBool()) };
+        },
+        .ComptimeInt => unreachable, // semantic analysis prevents this
+        .ComptimeFloat => unreachable, // semantic analysis prevents this
+        .Optional => {
+            if (typed_value.ty.isPtrLikeOptional()) {
+                if (typed_value.val.isNull())
+                    return MCValue{ .immediate = 0 };
+
+                var buf: Type.Payload.ElemType = undefined;
+                return self.genTypedValue(.{
+                    .ty = typed_value.ty.optionalChild(&buf),
+                    .val = typed_value.val,
+                });
+            } else if (typed_value.ty.abiSize(self.target.*) == 1) {
+                return MCValue{ .immediate = @boolToInt(typed_value.val.isNull()) };
+            }
+            return self.fail("TODO non pointer optionals", .{});
+        },
+        .Enum => {
+            if (typed_value.val.castTag(.enum_field_index)) |field_index| {
+                switch (typed_value.ty.tag()) {
+                    .enum_simple => {
+                        return MCValue{ .immediate = field_index.data };
+                    },
+                    .enum_full, .enum_nonexhaustive => {
+                        const enum_full = typed_value.ty.cast(Type.Payload.EnumFull).?.data;
+                        if (enum_full.values.count() != 0) {
+                            const tag_val = enum_full.values.keys()[field_index.data];
+                            return self.genTypedValue(.{ .ty = enum_full.tag_ty, .val = tag_val });
+                        } else {
+                            return MCValue{ .immediate = field_index.data };
+                        }
+                    },
+                    else => unreachable,
+                }
+            } else {
+                var int_tag_buffer: Type.Payload.Bits = undefined;
+                const int_tag_ty = typed_value.ty.intTagType(&int_tag_buffer);
+                return self.genTypedValue(.{ .ty = int_tag_ty, .val = typed_value.val });
+            }
+        },
+        .ErrorSet => {
+            switch (typed_value.val.tag()) {
+                .@"error" => {
+                    const err_name = typed_value.val.castTag(.@"error").?.data.name;
+                    const module = self.bin_file.options.module.?;
+                    const global_error_set = module.global_error_set;
+                    const error_index = global_error_set.get(err_name).?;
+                    return MCValue{ .immediate = error_index };
+                },
+                else => {
+                    // In this case we are rendering an error union which has a 0 bits payload.
+                    return MCValue{ .immediate = 0 };
+                },
+            }
+        },
+        .ErrorUnion => {
+            const error_type = typed_value.ty.errorUnionSet();
+            const payload_type = typed_value.ty.errorUnionPayload();
+            const sub_val = typed_value.val.castTag(.eu_payload).?.data;
+
+            if (!payload_type.hasCodeGenBits()) {
+                // We use the error type directly as the type.
+                return self.genTypedValue(.{ .ty = error_type, .val = sub_val });
+            }
+
+            return self.fail("TODO implement error union const of type '{}'", .{typed_value.ty});
+        },
+        else => return self.fail("TODO implement const of type '{}'", .{typed_value.ty}),
+    }
+}
+
+const CallMCValues = struct {
+    args: []MCValue,
+    return_value: MCValue,
+    stack_byte_count: u32,
+    stack_align: u32,
+
+    fn deinit(self: *CallMCValues, func: *Self) void {
+        func.gpa.free(self.args);
+        self.* = undefined;
+    }
+};
+
+/// Caller must call `CallMCValues.deinit`.
+fn resolveCallingConventionValues(self: *Self, fn_ty: Type) !CallMCValues {
+    const cc = fn_ty.fnCallingConvention();
+    _ = cc;
+    const param_types = try self.gpa.alloc(Type, fn_ty.fnParamLen());
+    defer self.gpa.free(param_types);
+    fn_ty.fnParamTypes(param_types);
+    var result: CallMCValues = .{
+        .args = try self.gpa.alloc(MCValue, param_types.len),
+        // These undefined values must be populated before returning from this function.
+        .return_value = undefined,
+        .stack_byte_count = undefined,
+        .stack_align = undefined,
+    };
+    errdefer self.gpa.free(result.args);
+
+    const ret_ty = fn_ty.fnReturnType();
+
+    if (param_types.len != 0) {
+        return self.fail("TODO implement codegen parameters for {}", .{self.target.cpu.arch});
+    }
+
+    if (ret_ty.zigTypeTag() == .NoReturn) {
+        result.return_value = .{ .unreach = {} };
+    } else if (!ret_ty.hasCodeGenBits()) {
+        result.return_value = .{ .none = {} };
+    } else return self.fail("TODO implement codegen return values for {}", .{self.target.cpu.arch});
+    return result;
+}
+
+/// TODO support scope overrides. Also note this logic is duplicated with `Module.wantSafety`.
+fn wantSafety(self: *Self) bool {
+    return switch (self.bin_file.options.optimize_mode) {
+        .Debug => true,
+        .ReleaseSafe => true,
+        .ReleaseFast => false,
+        .ReleaseSmall => false,
+    };
+}
+
+fn fail(self: *Self, comptime format: []const u8, args: anytype) InnerError {
+    @setCold(true);
+    assert(self.err_msg == null);
+    self.err_msg = try ErrorMsg.create(self.bin_file.allocator, self.src_loc, format, args);
+    return error.CodegenFail;
+}
+
+fn failSymbol(self: *Self, comptime format: []const u8, args: anytype) InnerError {
+    @setCold(true);
+    assert(self.err_msg == null);
+    self.err_msg = try ErrorMsg.create(self.bin_file.allocator, self.src_loc, format, args);
+    return error.CodegenFail;
+}
+
+const Register = @import("bits.zig").Register;
+const Instruction = @import("bits.zig").Instruction;
+const callee_preserved_regs = @import("bits.zig").callee_preserved_regs;
+
+fn parseRegName(name: []const u8) ?Register {
+    if (@hasDecl(Register, "parseRegName")) {
+        return Register.parseRegName(name);
+    }
+    return std.meta.stringToEnum(Register, name);
+}
src/codegen.zig
@@ -106,7 +106,7 @@ pub fn generateFunction(
         //.r600 => return Function(.r600).generate(bin_file, src_loc, func, air, liveness, code, debug_output),
         //.amdgcn => return Function(.amdgcn).generate(bin_file, src_loc, func, air, liveness, code, debug_output),
         //.riscv32 => return Function(.riscv32).generate(bin_file, src_loc, func, air, liveness, code, debug_output),
-        .riscv64 => return Function(.riscv64).generate(bin_file, src_loc, func, air, liveness, code, debug_output),
+        .riscv64 => return @import("arch/riscv64/CodeGen.zig").generate(bin_file, src_loc, func, air, liveness, code, debug_output),
         //.sparc => return Function(.sparc).generate(bin_file, src_loc, func, air, liveness, code, debug_output),
         //.sparcv9 => return Function(.sparcv9).generate(bin_file, src_loc, func, air, liveness, code, debug_output),
         //.sparcel => return Function(.sparcel).generate(bin_file, src_loc, func, air, liveness, code, debug_output),
@@ -2123,9 +2123,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
                 .i386 => {
                     try self.code.append(0xcc); // int3
                 },
-                .riscv64 => {
-                    mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.ebreak.toU32());
-                },
                 .arm, .armeb => {
                     writeInt(u32, try self.code.addManyAsArray(4), Instruction.bkpt(0).toU32());
                 },
@@ -2153,34 +2150,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
             // on linking.
             if (self.bin_file.tag == link.File.Elf.base_tag or self.bin_file.tag == link.File.Coff.base_tag) {
                 switch (arch) {
-                    .riscv64 => {
-                        if (info.args.len > 0) return self.fail("TODO implement fn args for {}", .{self.target.cpu.arch});
-
-                        if (self.air.value(callee)) |func_value| {
-                            if (func_value.castTag(.function)) |func_payload| {
-                                const func = func_payload.data;
-
-                                const ptr_bits = self.target.cpu.arch.ptrBitWidth();
-                                const ptr_bytes: u64 = @divExact(ptr_bits, 8);
-                                const got_addr = if (self.bin_file.cast(link.File.Elf)) |elf_file| blk: {
-                                    const got = &elf_file.program_headers.items[elf_file.phdr_got_index.?];
-                                    break :blk @intCast(u32, got.p_vaddr + func.owner_decl.link.elf.offset_table_index * ptr_bytes);
-                                } else if (self.bin_file.cast(link.File.Coff)) |coff_file|
-                                    coff_file.offset_table_virtual_address + func.owner_decl.link.coff.offset_table_index * ptr_bytes
-                                else
-                                    unreachable;
-
-                                try self.genSetReg(Type.initTag(.usize), .ra, .{ .memory = got_addr });
-                                mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.jalr(.ra, 0, .ra).toU32());
-                            } else if (func_value.castTag(.extern_fn)) |_| {
-                                return self.fail("TODO implement calling extern functions", .{});
-                            } else {
-                                return self.fail("TODO implement calling bitcasted functions", .{});
-                            }
-                        } else {
-                            return self.fail("TODO implement calling runtime known function pointer", .{});
-                        }
-                    },
                     .arm, .armeb => {
                         for (info.args) |mc_arg, arg_i| {
                             const arg = args[arg_i];
@@ -2287,9 +2256,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
                 .i386 => {
                     try self.code.append(0xc3); // ret
                 },
-                .riscv64 => {
-                    mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.jalr(.zero, 0, .ra).toU32());
-                },
                 .arm, .armeb => {
                     // Just add space for an instruction, patch this later
                     try self.code.resize(self.code.items.len + 4);
@@ -2969,42 +2935,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
                         break :result MCValue{ .none = {} };
                     }
                 },
-                .riscv64 => result: {
-                    for (args) |arg| {
-                        const input = zir.extraData(Zir.Inst.Asm.Input, extra_i);
-                        extra_i = input.end;
-                        const constraint = zir.nullTerminatedString(input.data.constraint);
-
-                        if (constraint.len < 3 or constraint[0] != '{' or constraint[constraint.len - 1] != '}') {
-                            return self.fail("unrecognized asm input constraint: '{s}'", .{constraint});
-                        }
-                        const reg_name = constraint[1 .. constraint.len - 1];
-                        const reg = parseRegName(reg_name) orelse
-                            return self.fail("unrecognized register: '{s}'", .{reg_name});
-
-                        const arg_mcv = try self.resolveInst(arg);
-                        try self.register_manager.getReg(reg, null);
-                        try self.genSetReg(self.air.typeOf(arg), reg, arg_mcv);
-                    }
-
-                    if (mem.eql(u8, asm_source, "ecall")) {
-                        mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.ecall.toU32());
-                    } else {
-                        return self.fail("TODO implement support for more riscv64 assembly instructions", .{});
-                    }
-
-                    if (output_constraint) |output| {
-                        if (output.len < 4 or output[0] != '=' or output[1] != '{' or output[output.len - 1] != '}') {
-                            return self.fail("unrecognized asm output constraint: '{s}'", .{output});
-                        }
-                        const reg_name = output[2 .. output.len - 1];
-                        const reg = parseRegName(reg_name) orelse
-                            return self.fail("unrecognized register: '{s}'", .{reg_name});
-                        break :result MCValue{ .register = reg };
-                    } else {
-                        break :result MCValue{ .none = {} };
-                    }
-                },
                 .i386 => result: {
                     for (args) |arg| {
                         const input = zir.extraData(Zir.Inst.Asm.Input, extra_i);
@@ -3311,49 +3241,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
                     },
                     else => return self.fail("TODO implement getSetReg for arm {}", .{mcv}),
                 },
-                .riscv64 => switch (mcv) {
-                    .dead => unreachable,
-                    .ptr_stack_offset => unreachable,
-                    .ptr_embedded_in_code => unreachable,
-                    .unreach, .none => return, // Nothing to do.
-                    .undef => {
-                        if (!self.wantSafety())
-                            return; // The already existing value will do just fine.
-                        // Write the debug undefined value.
-                        return self.genSetReg(ty, reg, .{ .immediate = 0xaaaaaaaaaaaaaaaa });
-                    },
-                    .immediate => |unsigned_x| {
-                        const x = @bitCast(i64, unsigned_x);
-                        if (math.minInt(i12) <= x and x <= math.maxInt(i12)) {
-                            mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.addi(reg, .zero, @truncate(i12, x)).toU32());
-                            return;
-                        }
-                        if (math.minInt(i32) <= x and x <= math.maxInt(i32)) {
-                            const lo12 = @truncate(i12, x);
-                            const carry: i32 = if (lo12 < 0) 1 else 0;
-                            const hi20 = @truncate(i20, (x >> 12) +% carry);
-
-                            // TODO: add test case for 32-bit immediate
-                            mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.lui(reg, hi20).toU32());
-                            mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.addi(reg, reg, lo12).toU32());
-                            return;
-                        }
-                        // li rd, immediate
-                        // "Myriad sequences"
-                        return self.fail("TODO genSetReg 33-64 bit immediates for riscv64", .{}); // glhf
-                    },
-                    .memory => |addr| {
-                        // The value is in memory at a hard-coded address.
-                        // If the type is a pointer, it means the pointer address is at this memory location.
-                        try self.genSetReg(ty, reg, .{ .immediate = addr });
-
-                        mem.writeIntLittle(u32, try self.code.addManyAsArray(4), Instruction.ld(reg, 0, reg).toU32());
-                        // LOAD imm=[i12 offset = 0], rs1 =
-
-                        // return self.fail("TODO implement genSetReg memory for riscv64");
-                    },
-                    else => return self.fail("TODO implement getSetReg for riscv64 {}", .{mcv}),
-                },
                 else => return self.fail("TODO implement getSetReg for {}", .{self.target.cpu.arch}),
             }
         }
@@ -3762,7 +3649,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
 
         const Register = switch (arch) {
             .i386 => @import("arch/x86/bits.zig").Register,
-            .riscv64 => @import("arch/riscv64/bits.zig").Register,
             .arm, .armeb => @import("arch/arm/bits.zig").Register,
             else => enum {
                 dummy,
@@ -3775,7 +3661,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
         };
 
         const Instruction = switch (arch) {
-            .riscv64 => @import("arch/riscv64/bits.zig").Instruction,
             .arm, .armeb => @import("arch/arm/bits.zig").Instruction,
             else => void,
         };
@@ -3787,7 +3672,6 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
 
         const callee_preserved_regs = switch (arch) {
             .i386 => @import("arch/x86/bits.zig").callee_preserved_regs,
-            .riscv64 => @import("arch/riscv64/bits.zig").callee_preserved_regs,
             .arm, .armeb => @import("arch/arm/bits.zig").callee_preserved_regs,
             else => [_]Register{},
         };