Commit 2587474717

Andrew Kelley <andrew@ziglang.org>
2022-04-14 19:12:45
stage2: progress towards stage3
* The `@bitCast` workaround is removed in favor of `@ptrCast` properly doing element casting for slice element types. This required an enhancement both to stage1 and stage2. * stage1 incorrectly accepts `.{}` instead of `{}`. stage2 code that abused this is fixed. * Make some parameters comptime to support functions in switch expressions (as opposed to making them function pointers). * Avoid relying on local temporaries being mutable. * Workarounds for when stage1 and stage2 disagree on function pointer types. * Workaround recursive formatting bug with a `@panic("TODO")`. * Remove unreachable `else` prongs for some inferred error sets. All in effort towards #89.
1 parent 0739770
lib/std/fmt.zig
@@ -766,12 +766,10 @@ fn formatFloatValue(
     } else if (comptime std.mem.eql(u8, fmt, "d")) {
         formatFloatDecimal(value, options, buf_stream.writer()) catch |err| switch (err) {
             error.NoSpaceLeft => unreachable,
-            else => |e| return e,
         };
     } else if (comptime std.mem.eql(u8, fmt, "x")) {
         formatFloatHexadecimal(value, options, buf_stream.writer()) catch |err| switch (err) {
             error.NoSpaceLeft => unreachable,
-            else => |e| return e,
         };
     } else {
         @compileError("Unsupported format string '" ++ fmt ++ "' for type '" ++ @typeName(@TypeOf(value)) ++ "'");
lib/std/io.zig
@@ -9,7 +9,6 @@ const os = std.os;
 const fs = std.fs;
 const mem = std.mem;
 const meta = std.meta;
-const trait = meta.trait;
 const File = std.fs.File;
 
 pub const Mode = enum {
lib/std/rand.zig
@@ -66,9 +66,7 @@ pub const Random = struct {
 
     /// Returns a random value from an enum, evenly distributed.
     pub fn enumValue(r: Random, comptime EnumType: type) EnumType {
-        if (comptime !std.meta.trait.is(.Enum)(EnumType)) {
-            @compileError("Random.enumValue requires an enum type, not a " ++ @typeName(EnumType));
-        }
+        comptime assert(@typeInfo(EnumType) == .Enum);
 
         // We won't use int -> enum casting because enum elements can have
         //  arbitrary values.  Instead we'll randomly pick one of the type's values.
src/arch/aarch64/CodeGen.zig
@@ -2398,7 +2398,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallOptions.
     const pl_op = self.air.instructions.items(.data)[inst].pl_op;
     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]);
+    const args = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra.end..][0..extra.data.args_len]);
     const ty = self.air.typeOf(callee);
 
     const fn_ty = switch (ty.zigTypeTag()) {
@@ -2865,7 +2865,10 @@ fn airCondBr(self: *Self, inst: Air.Inst.Index) !void {
         // TODO track the new register / stack allocation
     }
 
-    self.branch_stack.pop().deinit(self.gpa);
+    {
+        var item = self.branch_stack.pop();
+        item.deinit(self.gpa);
+    }
 
     // We already took care of pl_op.operand earlier, so we're going
     // to pass .none here
@@ -3162,9 +3165,9 @@ fn airAsm(self: *Self, inst: Air.Inst.Index) !void {
     const is_volatile = @truncate(u1, extra.data.flags >> 31) != 0;
     const clobbers_len = @truncate(u31, extra.data.flags);
     var extra_i: usize = extra.end;
-    const outputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
+    const outputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
     extra_i += outputs.len;
-    const inputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
+    const inputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
     extra_i += inputs.len;
 
     const dead = !is_volatile and self.liveness.isUnused(inst);
@@ -3686,7 +3689,7 @@ fn airAggregateInit(self: *Self, inst: Air.Inst.Index) !void {
     const vector_ty = self.air.typeOfIndex(inst);
     const len = vector_ty.vectorLen();
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
-    const elements = @bitCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
+    const elements = @ptrCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
     const result: MCValue = res: {
         if (self.liveness.isUnused(inst)) break :res MCValue.dead;
         return self.fail("TODO implement airAggregateInit for {}", .{self.target.cpu.arch});
src/arch/arm/CodeGen.zig
@@ -3144,7 +3144,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallOptions.
     const pl_op = self.air.instructions.items(.data)[inst].pl_op;
     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]);
+    const args = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra.end..][0..extra.data.args_len]);
     const ty = self.air.typeOf(callee);
 
     const fn_ty = switch (ty.zigTypeTag()) {
@@ -3650,7 +3650,10 @@ fn airCondBr(self: *Self, inst: Air.Inst.Index) !void {
         // TODO track the new register / stack allocation
     }
 
-    self.branch_stack.pop().deinit(self.gpa);
+    {
+        var item = self.branch_stack.pop();
+        item.deinit(self.gpa);
+    }
 
     // We already took care of pl_op.operand earlier, so we're going
     // to pass .none here
@@ -3951,9 +3954,9 @@ fn airAsm(self: *Self, inst: Air.Inst.Index) !void {
     const is_volatile = @truncate(u1, extra.data.flags >> 31) != 0;
     const clobbers_len = @truncate(u31, extra.data.flags);
     var extra_i: usize = extra.end;
-    const outputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
+    const outputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
     extra_i += outputs.len;
-    const inputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
+    const inputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
     extra_i += inputs.len;
 
     const dead = !is_volatile and self.liveness.isUnused(inst);
@@ -4735,7 +4738,7 @@ fn airAggregateInit(self: *Self, inst: Air.Inst.Index) !void {
     const vector_ty = self.air.typeOfIndex(inst);
     const len = vector_ty.vectorLen();
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
-    const elements = @bitCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
+    const elements = @ptrCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
     const result: MCValue = res: {
         if (self.liveness.isUnused(inst)) break :res MCValue.dead;
         return self.fail("TODO implement airAggregateInit for arm", .{});
src/arch/arm/Emit.zig
@@ -2,6 +2,7 @@
 //! machine code
 
 const Emit = @This();
+const builtin = @import("builtin");
 const std = @import("std");
 const math = std.math;
 const Mir = @import("Mir.zig");
@@ -622,12 +623,17 @@ fn mirLoadStackArgument(emit: *Emit, inst: Mir.Inst.Index) !void {
             } else return emit.fail("TODO mirLoadStack larger offsets", .{});
 
             const ldr = switch (tag) {
-                .ldr_stack_argument => Instruction.ldr,
-                .ldrb_stack_argument => Instruction.ldrb,
+                .ldr_stack_argument => &Instruction.ldr,
+                .ldrb_stack_argument => &Instruction.ldrb,
                 else => unreachable,
             };
 
-            try emit.writeInstruction(ldr(
+            const ldr_workaround = switch (builtin.zig_backend) {
+                .stage1 => ldr.*,
+                else => ldr,
+            };
+
+            try emit.writeInstruction(ldr_workaround(
                 cond,
                 r_stack_offset.rt,
                 .fp,
@@ -643,13 +649,18 @@ fn mirLoadStackArgument(emit: *Emit, inst: Mir.Inst.Index) !void {
             } else return emit.fail("TODO mirLoadStack larger offsets", .{});
 
             const ldr = switch (tag) {
-                .ldrh_stack_argument => Instruction.ldrh,
-                .ldrsb_stack_argument => Instruction.ldrsb,
-                .ldrsh_stack_argument => Instruction.ldrsh,
+                .ldrh_stack_argument => &Instruction.ldrh,
+                .ldrsb_stack_argument => &Instruction.ldrsb,
+                .ldrsh_stack_argument => &Instruction.ldrsh,
                 else => unreachable,
             };
 
-            try emit.writeInstruction(ldr(
+            const ldr_workaround = switch (builtin.zig_backend) {
+                .stage1 => ldr.*,
+                else => ldr,
+            };
+
+            try emit.writeInstruction(ldr_workaround(
                 cond,
                 r_stack_offset.rt,
                 .fp,
src/arch/riscv64/CodeGen.zig
@@ -1640,7 +1640,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallOptions.
     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]);
+    const args = @ptrCast([]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);
@@ -2075,9 +2075,9 @@ fn airAsm(self: *Self, inst: Air.Inst.Index) !void {
     const is_volatile = @truncate(u1, extra.data.flags >> 31) != 0;
     const clobbers_len = @truncate(u31, extra.data.flags);
     var extra_i: usize = extra.end;
-    const outputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
+    const outputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
     extra_i += outputs.len;
-    const inputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
+    const inputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
     extra_i += inputs.len;
 
     const dead = !is_volatile and self.liveness.isUnused(inst);
@@ -2413,7 +2413,7 @@ fn airAggregateInit(self: *Self, inst: Air.Inst.Index) !void {
     const vector_ty = self.air.typeOfIndex(inst);
     const len = vector_ty.vectorLen();
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
-    const elements = @bitCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
+    const elements = @ptrCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
     const result: MCValue = res: {
         if (self.liveness.isUnused(inst)) break :res MCValue.dead;
         return self.fail("TODO implement airAggregateInit for riscv64", .{});
src/arch/wasm/CodeGen.zig
@@ -2425,7 +2425,7 @@ fn airSwitchBr(self: *Self, inst: Air.Inst.Index) InnerError!WValue {
     var highest_maybe: ?i32 = null;
     while (case_i < switch_br.data.cases_len) : (case_i += 1) {
         const case = self.air.extraData(Air.SwitchBr.Case, extra_index);
-        const items = @bitCast([]const Air.Inst.Ref, self.air.extra[case.end..][0..case.data.items_len]);
+        const items = @ptrCast([]const Air.Inst.Ref, self.air.extra[case.end..][0..case.data.items_len]);
         const case_body = self.air.extra[case.end + items.len ..][0..case.data.body_len];
         extra_index = case.end + items.len + case_body.len;
         const values = try self.gpa.alloc(CaseValue, items.len);
@@ -3328,7 +3328,7 @@ fn airAggregateInit(self: *Self, inst: Air.Inst.Index) InnerError!WValue {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const result_ty = self.air.typeOfIndex(inst);
     const len = @intCast(usize, result_ty.arrayLen());
-    const elements = @bitCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
+    const elements = @ptrCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
 
     switch (result_ty.zigTypeTag()) {
         .Vector => return self.fail("TODO: Wasm backend: implement airAggregateInit for vectors", .{}),
src/arch/x86_64/CodeGen.zig
@@ -3501,7 +3501,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallOptions.
     const pl_op = self.air.instructions.items(.data)[inst].pl_op;
     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]);
+    const args = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra.end..][0..extra.data.args_len]);
     const ty = self.air.typeOf(callee);
 
     const fn_ty = switch (ty.zigTypeTag()) {
@@ -3684,7 +3684,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallOptions.
                     .ops = (Mir.Ops{
                         .flags = 0b01,
                     }).encode(),
-                    .data = .{ .imm = @bitCast(i32, @intCast(u32, fn_got_addr)) },
+                    .data = .{ .imm = @intCast(u32, fn_got_addr) },
                 });
             } else return self.fail("TODO implement calling extern fn on plan9", .{});
         } else {
@@ -4220,7 +4220,10 @@ fn airCondBr(self: *Self, inst: Air.Inst.Index) !void {
         // TODO track the new register / stack allocation
     }
 
-    self.branch_stack.pop().deinit(self.gpa);
+    {
+        var item = self.branch_stack.pop();
+        item.deinit(self.gpa);
+    }
 
     // We already took care of pl_op.operand earlier, so we're going
     // to pass .none here
@@ -4562,7 +4565,7 @@ fn airSwitch(self: *Self, inst: Air.Inst.Index) !void {
 
     while (case_i < switch_br.data.cases_len) : (case_i += 1) {
         const case = self.air.extraData(Air.SwitchBr.Case, extra_index);
-        const items = @bitCast([]const Air.Inst.Ref, self.air.extra[case.end..][0..case.data.items_len]);
+        const items = @ptrCast([]const Air.Inst.Ref, self.air.extra[case.end..][0..case.data.items_len]);
         const case_body = self.air.extra[case.end + items.len ..][0..case.data.body_len];
         extra_index = case.end + items.len + case_body.len;
 
@@ -4615,7 +4618,10 @@ fn airSwitch(self: *Self, inst: Air.Inst.Index) !void {
     if (switch_br.data.else_body_len > 0) {
         const else_body = self.air.extra[extra_index..][0..switch_br.data.else_body_len];
         try self.branch_stack.append(.{});
-        defer self.branch_stack.pop().deinit(self.gpa);
+        defer {
+            var item = self.branch_stack.pop();
+            item.deinit(self.gpa);
+        }
 
         const else_deaths = liveness.deaths.len - 1;
         try self.ensureProcessDeathCapacity(liveness.deaths[else_deaths].len);
@@ -4705,9 +4711,9 @@ fn airAsm(self: *Self, inst: Air.Inst.Index) !void {
     const is_volatile = @truncate(u1, extra.data.flags >> 31) != 0;
     const clobbers_len = @truncate(u31, extra.data.flags);
     var extra_i: usize = extra.end;
-    const outputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
+    const outputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
     extra_i += outputs.len;
-    const inputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
+    const inputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
     extra_i += inputs.len;
 
     const dead = !is_volatile and self.liveness.isUnused(inst);
@@ -5975,7 +5981,7 @@ fn airAggregateInit(self: *Self, inst: Air.Inst.Index) !void {
     const result_ty = self.air.typeOfIndex(inst);
     const len = @intCast(usize, result_ty.arrayLen());
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
-    const elements = @bitCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
+    const elements = @ptrCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
     const abi_size = @intCast(u32, result_ty.abiSize(self.target.*));
     const abi_align = result_ty.abiAlignment(self.target.*);
     const result: MCValue = res: {
src/codegen/c.zig
@@ -220,6 +220,9 @@ fn formatIdent(
 }
 
 pub fn fmtIdent(ident: []const u8) std.fmt.Formatter(formatIdent) {
+    if (builtin.zig_backend != .stage1) {
+        @panic("TODO");
+    }
     return .{ .data = ident };
 }
 
@@ -2310,7 +2313,6 @@ fn airWrapOp(
                 const val = -1 * std.math.pow(i64, 2, @intCast(i64, bits - 1));
                 break :blk std.fmt.bufPrint(&min_buf, "{d}", .{val}) catch |err| switch (err) {
                     error.NoSpaceLeft => unreachable,
-                    else => |e| return e,
                 };
             },
         },
@@ -2336,7 +2338,6 @@ fn airWrapOp(
             const val = std.math.pow(u64, 2, pow_bits) - 1;
             break :blk std.fmt.bufPrint(&max_buf, "{}", .{val}) catch |err| switch (err) {
                 error.NoSpaceLeft => unreachable,
-                else => |e| return e,
             };
         },
     };
@@ -2418,7 +2419,6 @@ fn airSatOp(f: *Function, inst: Air.Inst.Index, fn_op: [*:0]const u8) !CValue {
                 const val = -1 * std.math.pow(i65, 2, @intCast(i65, bits - 1));
                 break :blk std.fmt.bufPrint(&min_buf, "{d}", .{val}) catch |err| switch (err) {
                     error.NoSpaceLeft => unreachable,
-                    else => |e| return e,
                 };
             },
         },
@@ -2444,7 +2444,6 @@ fn airSatOp(f: *Function, inst: Air.Inst.Index, fn_op: [*:0]const u8) !CValue {
             const val = std.math.pow(u65, 2, pow_bits) - 1;
             break :blk std.fmt.bufPrint(&max_buf, "{}", .{val}) catch |err| switch (err) {
                 error.NoSpaceLeft => unreachable,
-                else => |e| return e,
             };
         },
     };
@@ -2702,7 +2701,7 @@ fn airCall(
     }
     const pl_op = f.air.instructions.items(.data)[inst].pl_op;
     const extra = f.air.extraData(Air.Call, pl_op.payload);
-    const args = @bitCast([]const Air.Inst.Ref, f.air.extra[extra.end..][0..extra.data.args_len]);
+    const args = @ptrCast([]const Air.Inst.Ref, f.air.extra[extra.end..][0..extra.data.args_len]);
     const callee_ty = f.air.typeOf(pl_op.operand);
     const fn_ty = switch (callee_ty.zigTypeTag()) {
         .Fn => callee_ty,
@@ -2959,7 +2958,7 @@ fn airSwitchBr(f: *Function, inst: Air.Inst.Index) !CValue {
     var case_i: u32 = 0;
     while (case_i < switch_br.data.cases_len) : (case_i += 1) {
         const case = f.air.extraData(Air.SwitchBr.Case, extra_index);
-        const items = @bitCast([]const Air.Inst.Ref, f.air.extra[case.end..][0..case.data.items_len]);
+        const items = @ptrCast([]const Air.Inst.Ref, f.air.extra[case.end..][0..case.data.items_len]);
         const case_body = f.air.extra[case.end + items.len ..][0..case.data.body_len];
         extra_index = case.end + case.data.items_len + case_body.len;
 
@@ -2990,9 +2989,9 @@ fn airAsm(f: *Function, inst: Air.Inst.Index) !CValue {
     const is_volatile = @truncate(u1, extra.data.flags >> 31) != 0;
     const clobbers_len = @truncate(u31, extra.data.flags);
     var extra_i: usize = extra.end;
-    const outputs = @bitCast([]const Air.Inst.Ref, f.air.extra[extra_i..][0..extra.data.outputs_len]);
+    const outputs = @ptrCast([]const Air.Inst.Ref, f.air.extra[extra_i..][0..extra.data.outputs_len]);
     extra_i += outputs.len;
-    const inputs = @bitCast([]const Air.Inst.Ref, f.air.extra[extra_i..][0..extra.data.inputs_len]);
+    const inputs = @ptrCast([]const Air.Inst.Ref, f.air.extra[extra_i..][0..extra.data.inputs_len]);
     extra_i += inputs.len;
 
     if (!is_volatile and f.liveness.isUnused(inst)) return CValue.none;
@@ -3860,7 +3859,7 @@ fn airAggregateInit(f: *Function, inst: Air.Inst.Index) !CValue {
     const ty_pl = f.air.instructions.items(.data)[inst].ty_pl;
     const vector_ty = f.air.getRefType(ty_pl.ty);
     const len = vector_ty.vectorLen();
-    const elements = @bitCast([]const Air.Inst.Ref, f.air.extra[ty_pl.payload..][0..len]);
+    const elements = @ptrCast([]const Air.Inst.Ref, f.air.extra[ty_pl.payload..][0..len]);
 
     const writer = f.object.writer();
     const local = try f.allocLocal(inst_ty, .Const);
src/codegen/llvm.zig
@@ -3657,7 +3657,7 @@ pub const FuncGen = struct {
     fn airCall(self: *FuncGen, inst: Air.Inst.Index, attr: llvm.CallAttr) !?*const llvm.Value {
         const pl_op = self.air.instructions.items(.data)[inst].pl_op;
         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]);
+        const args = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra.end..][0..extra.data.args_len]);
         const callee_ty = self.air.typeOf(pl_op.operand);
         const zig_fn_ty = switch (callee_ty.zigTypeTag()) {
             .Fn => callee_ty,
@@ -4037,7 +4037,7 @@ pub const FuncGen = struct {
 
         while (case_i < switch_br.data.cases_len) : (case_i += 1) {
             const case = self.air.extraData(Air.SwitchBr.Case, extra_index);
-            const items = @bitCast([]const Air.Inst.Ref, self.air.extra[case.end..][0..case.data.items_len]);
+            const items = @ptrCast([]const Air.Inst.Ref, self.air.extra[case.end..][0..case.data.items_len]);
             const case_body = self.air.extra[case.end + items.len ..][0..case.data.body_len];
             extra_index = case.end + case.data.items_len + case_body.len;
 
@@ -4538,9 +4538,9 @@ pub const FuncGen = struct {
 
         if (!is_volatile and self.liveness.isUnused(inst)) return null;
 
-        const outputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
+        const outputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
         extra_i += outputs.len;
-        const inputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
+        const inputs = @ptrCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
         extra_i += inputs.len;
 
         if (outputs.len > 1) {
@@ -6660,7 +6660,7 @@ pub const FuncGen = struct {
         const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
         const result_ty = self.air.typeOfIndex(inst);
         const len = @intCast(usize, result_ty.arrayLen());
-        const elements = @bitCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
+        const elements = @ptrCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
         const llvm_result_ty = try self.dg.llvmType(result_ty);
         const target = self.dg.module.getTarget();
 
src/link/MachO/fat.zig
@@ -40,7 +40,6 @@ pub fn getLibraryOffset(reader: anytype, target: std.Target) !u64 {
         // fine because we can keep looking for one that might match.
         const lib_arch = decodeArch(fat_arch.cputype, false) catch |err| switch (err) {
             error.UnsupportedCpuArchitecture => continue,
-            else => |e| return e,
         };
         if (lib_arch == target.cpu.arch) {
             // We have found a matching architecture!
src/link/MachO/Object.zig
@@ -625,7 +625,6 @@ pub fn parseDataInCode(self: *Object, allocator: Allocator) !void {
     while (true) {
         const dice = reader.readStruct(macho.data_in_code_entry) catch |err| switch (err) {
             error.EndOfStream => break,
-            else => |e| return e,
         };
         try self.data_in_code_entries.append(allocator, dice);
     }
src/link/C.zig
@@ -89,8 +89,9 @@ pub fn deinit(self: *C) void {
 
 pub fn freeDecl(self: *C, decl: *Module.Decl) void {
     const gpa = self.base.allocator;
-    if (self.decl_table.fetchSwapRemove(decl)) |*kv| {
-        kv.value.deinit(gpa);
+    if (self.decl_table.fetchSwapRemove(decl)) |kv| {
+        var decl_block = kv.value;
+        decl_block.deinit(gpa);
     }
 }
 
src/link/Elf.zig
@@ -2482,7 +2482,7 @@ pub fn lowerUnnamedConst(self: *Elf, typed_value: TypedValue, decl: *Module.Decl
     try self.atom_by_index_table.putNoClobber(self.base.allocator, atom.local_sym_index, atom);
 
     const res = try codegen.generateSymbol(&self.base, decl.srcLoc(), typed_value, &code_buffer, .{
-        .none = .{},
+        .none = {},
     }, .{
         .parent_atom_index = atom.local_sym_index,
     });
src/link/Plan9.zig
@@ -307,7 +307,7 @@ pub fn updateDecl(self: *Plan9, module: *Module, decl: *Module.Decl) !void {
     const res = try codegen.generateSymbol(&self.base, decl.srcLoc(), .{
         .ty = decl.ty,
         .val = decl_val,
-    }, &code_buffer, .{ .none = .{} }, .{
+    }, &code_buffer, .{ .none = {} }, .{
         .parent_atom_index = @intCast(u32, sym_index),
     });
     const code = switch (res) {
src/link/Wasm.zig
@@ -2551,7 +2551,8 @@ fn emitSymbolTable(self: *Wasm, file: fs.File, arena: Allocator, symbol_table: *
         .iov_base = payload.items.ptr,
         .iov_len = payload.items.len,
     };
-    try file.writevAll(&.{iovec});
+    var iovecs = [_]std.os.iovec_const{iovec};
+    try file.writevAll(&iovecs);
 }
 
 fn emitSegmentInfo(self: *Wasm, file: fs.File, arena: Allocator) !void {
@@ -2576,7 +2577,8 @@ fn emitSegmentInfo(self: *Wasm, file: fs.File, arena: Allocator) !void {
         .iov_base = payload.items.ptr,
         .iov_len = payload.items.len,
     };
-    try file.writevAll(&.{iovec});
+    var iovecs = [_]std.os.iovec_const{iovec};
+    try file.writevAll(&iovecs);
 }
 
 fn getULEB128Size(uint_value: anytype) u32 {
@@ -2635,12 +2637,14 @@ fn emitCodeRelocations(
     var buf: [5]u8 = undefined;
     leb.writeUnsignedFixed(5, &buf, count);
     try payload.insertSlice(reloc_start, &buf);
-    const iovec: std.os.iovec_const = .{
-        .iov_base = payload.items.ptr,
-        .iov_len = payload.items.len,
+    var iovecs = [_]std.os.iovec_const{
+        .{
+            .iov_base = payload.items.ptr,
+            .iov_len = payload.items.len,
+        },
     };
     const header_offset = try reserveCustomSectionHeader(file);
-    try file.writevAll(&.{iovec});
+    try file.writevAll(&iovecs);
     const size = @intCast(u32, payload.items.len);
     try writeCustomSectionHeader(file, header_offset, size);
 }
@@ -2694,12 +2698,14 @@ fn emitDataRelocations(
     var buf: [5]u8 = undefined;
     leb.writeUnsignedFixed(5, &buf, count);
     try payload.insertSlice(reloc_start, &buf);
-    const iovec: std.os.iovec_const = .{
-        .iov_base = payload.items.ptr,
-        .iov_len = payload.items.len,
+    var iovecs = [_]std.os.iovec_const{
+        .{
+            .iov_base = payload.items.ptr,
+            .iov_len = payload.items.len,
+        },
     };
     const header_offset = try reserveCustomSectionHeader(file);
-    try file.writevAll(&.{iovec});
+    try file.writevAll(&iovecs);
     const size = @intCast(u32, payload.items.len);
     try writeCustomSectionHeader(file, header_offset, size);
 }
src/stage1/ir.cpp
@@ -23052,6 +23052,12 @@ static Stage1AirInst *ir_analyze_instruction_ptr_cast(IrAnalyze *ira, Stage1ZirI
     if (type_is_invalid(src_type))
         return ira->codegen->invalid_inst_gen;
 
+    // This logic is not quite right; this is just to get stage1 to accept valid code
+    // we use in the self-hosted compiler.
+    if (is_slice(dest_type) && is_slice(src_type)) {
+        return ir_analyze_bit_cast(ira, instruction->base.scope, instruction->base.source_node, ptr, dest_type);
+    }
+
     bool keep_bigger_alignment = true;
     return ir_analyze_ptr_cast(ira, instruction->base.scope, instruction->base.source_node, ptr,
             instruction->ptr->source_node, dest_type, dest_type_value->source_node,
src/AstGen.zig
@@ -85,12 +85,12 @@ fn reserveExtra(astgen: *AstGen, size: usize) Allocator.Error!u32 {
 }
 
 fn appendRefs(astgen: *AstGen, refs: []const Zir.Inst.Ref) !void {
-    const coerced = @bitCast([]const u32, refs);
+    const coerced = @ptrCast([]const u32, refs);
     return astgen.extra.appendSlice(astgen.gpa, coerced);
 }
 
 fn appendRefsAssumeCapacity(astgen: *AstGen, refs: []const Zir.Inst.Ref) void {
-    const coerced = @bitCast([]const u32, refs);
+    const coerced = @ptrCast([]const u32, refs);
     astgen.extra.appendSliceAssumeCapacity(coerced);
 }
 
src/link.zig
@@ -649,6 +649,11 @@ pub const File = struct {
         }
     }
 
+    pub const UpdateDeclExportsError = error{
+        OutOfMemory,
+        AnalysisFail,
+    };
+
     /// May be called before or after updateDecl, but must be called after
     /// allocateDeclIndexes for any given Decl.
     pub fn updateDeclExports(
@@ -656,7 +661,7 @@ pub const File = struct {
         module: *Module,
         decl: *Module.Decl,
         exports: []const *Module.Export,
-    ) !void {
+    ) UpdateDeclExportsError!void {
         log.debug("updateDeclExports {*} ({s})", .{ decl, decl.name });
         assert(decl.has_tv);
         switch (base.tag) {
src/Liveness.zig
@@ -454,7 +454,7 @@ fn analyzeInst(
             const inst_data = inst_datas[inst].pl_op;
             const callee = inst_data.operand;
             const extra = a.air.extraData(Air.Call, inst_data.payload);
-            const args = @bitCast([]const Air.Inst.Ref, a.air.extra[extra.end..][0..extra.data.args_len]);
+            const args = @ptrCast([]const Air.Inst.Ref, a.air.extra[extra.end..][0..extra.data.args_len]);
             if (args.len + 1 <= bpi - 1) {
                 var buf = [1]Air.Inst.Ref{.none} ** (bpi - 1);
                 buf[0] = callee;
@@ -495,7 +495,7 @@ fn analyzeInst(
             const ty_pl = inst_datas[inst].ty_pl;
             const aggregate_ty = a.air.getRefType(ty_pl.ty);
             const len = @intCast(usize, aggregate_ty.arrayLen());
-            const elements = @bitCast([]const Air.Inst.Ref, a.air.extra[ty_pl.payload..][0..len]);
+            const elements = @ptrCast([]const Air.Inst.Ref, a.air.extra[ty_pl.payload..][0..len]);
 
             if (elements.len <= bpi - 1) {
                 var buf = [1]Air.Inst.Ref{.none} ** (bpi - 1);
@@ -571,9 +571,9 @@ fn analyzeInst(
         .assembly => {
             const extra = a.air.extraData(Air.Asm, inst_datas[inst].ty_pl.payload);
             var extra_i: usize = extra.end;
-            const outputs = @bitCast([]const Air.Inst.Ref, a.air.extra[extra_i..][0..extra.data.outputs_len]);
+            const outputs = @ptrCast([]const Air.Inst.Ref, a.air.extra[extra_i..][0..extra.data.outputs_len]);
             extra_i += outputs.len;
-            const inputs = @bitCast([]const Air.Inst.Ref, a.air.extra[extra_i..][0..extra.data.inputs_len]);
+            const inputs = @ptrCast([]const Air.Inst.Ref, a.air.extra[extra_i..][0..extra.data.inputs_len]);
             extra_i += inputs.len;
 
             simple: {
src/Module.zig
@@ -4593,7 +4593,7 @@ pub fn clearDecl(
                 .c => .{ .c = {} },
                 .wasm => .{ .wasm = link.File.Wasm.FnData.empty },
                 .spirv => .{ .spirv = .{} },
-                .nvptx => .{ .nvptx = .{} },
+                .nvptx => .{ .nvptx = {} },
             };
         }
         if (decl.getInnerNamespace()) |namespace| {
@@ -4975,7 +4975,7 @@ pub fn allocateNewDecl(
             .c => .{ .c = {} },
             .wasm => .{ .wasm = link.File.Wasm.FnData.empty },
             .spirv => .{ .spirv = .{} },
-            .nvptx => .{ .nvptx = .{} },
+            .nvptx => .{ .nvptx = {} },
         },
         .generation = 0,
         .is_pub = false,
src/print_air.zig
@@ -328,7 +328,7 @@ const Writer = struct {
         const ty_pl = w.air.instructions.items(.data)[inst].ty_pl;
         const vector_ty = w.air.getRefType(ty_pl.ty);
         const len = @intCast(usize, vector_ty.arrayLen());
-        const elements = @bitCast([]const Air.Inst.Ref, w.air.extra[ty_pl.payload..][0..len]);
+        const elements = @ptrCast([]const Air.Inst.Ref, w.air.extra[ty_pl.payload..][0..len]);
 
         try s.print("{}, [", .{vector_ty.fmtDebug()});
         for (elements) |elem, i| {
@@ -533,9 +533,9 @@ const Writer = struct {
             try s.writeAll(", volatile");
         }
 
-        const outputs = @bitCast([]const Air.Inst.Ref, w.air.extra[extra_i..][0..extra.data.outputs_len]);
+        const outputs = @ptrCast([]const Air.Inst.Ref, w.air.extra[extra_i..][0..extra.data.outputs_len]);
         extra_i += outputs.len;
-        const inputs = @bitCast([]const Air.Inst.Ref, w.air.extra[extra_i..][0..extra.data.inputs_len]);
+        const inputs = @ptrCast([]const Air.Inst.Ref, w.air.extra[extra_i..][0..extra.data.inputs_len]);
         extra_i += inputs.len;
 
         for (outputs) |output| {
@@ -604,7 +604,7 @@ const Writer = struct {
     fn writeCall(w: *Writer, s: anytype, inst: Air.Inst.Index) @TypeOf(s).Error!void {
         const pl_op = w.air.instructions.items(.data)[inst].pl_op;
         const extra = w.air.extraData(Air.Call, pl_op.payload);
-        const args = @bitCast([]const Air.Inst.Ref, w.air.extra[extra.end..][0..extra.data.args_len]);
+        const args = @ptrCast([]const Air.Inst.Ref, w.air.extra[extra.end..][0..extra.data.args_len]);
         try w.writeOperand(s, inst, 0, pl_op.operand);
         try s.writeAll(", [");
         for (args) |arg, i| {
@@ -674,7 +674,7 @@ const Writer = struct {
 
         while (case_i < switch_br.data.cases_len) : (case_i += 1) {
             const case = w.air.extraData(Air.SwitchBr.Case, extra_index);
-            const items = @bitCast([]const Air.Inst.Ref, w.air.extra[case.end..][0..case.data.items_len]);
+            const items = @ptrCast([]const Air.Inst.Ref, w.air.extra[case.end..][0..case.data.items_len]);
             const case_body = w.air.extra[case.end + items.len ..][0..case.data.body_len];
             extra_index = case.end + case.data.items_len + case_body.len;
 
src/Sema.zig
@@ -14110,21 +14110,27 @@ fn zirPtrCast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air
 
     try sema.checkPtrType(block, dest_ty_src, dest_ty);
     try sema.checkPtrOperand(block, operand_src, operand_ty);
-    if (dest_ty.isSlice()) {
+
+    const dest_is_slice = dest_ty.isSlice();
+    const operand_is_slice = operand_ty.isSlice();
+    if (dest_is_slice and !operand_is_slice) {
         return sema.fail(block, dest_ty_src, "illegal pointer cast to slice", .{});
     }
-    const ptr = if (operand_ty.isSlice())
+    const ptr = if (operand_is_slice and !dest_is_slice)
         try sema.analyzeSlicePtr(block, operand_src, operand, operand_ty)
     else
         operand;
 
-    try sema.resolveTypeLayout(block, dest_ty_src, dest_ty.elemType2());
+    const dest_elem_ty = dest_ty.elemType2();
+    try sema.resolveTypeLayout(block, dest_ty_src, dest_elem_ty);
     const dest_align = dest_ty.ptrAlignment(target);
-    try sema.resolveTypeLayout(block, operand_src, operand_ty.elemType2());
+
+    const operand_elem_ty = operand_ty.elemType2();
+    try sema.resolveTypeLayout(block, operand_src, operand_elem_ty);
     const operand_align = operand_ty.ptrAlignment(target);
 
     // If the destination is less aligned than the source, preserve the source alignment
-    var aligned_dest_ty = if (operand_align <= dest_align) dest_ty else blk: {
+    const aligned_dest_ty = if (operand_align <= dest_align) dest_ty else blk: {
         // Unwrap the pointer (or pointer-like optional) type, set alignment, and re-wrap into result
         if (dest_ty.zigTypeTag() == .Optional) {
             var buf: Type.Payload.ElemType = undefined;
@@ -14138,6 +14144,16 @@ fn zirPtrCast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air
         }
     };
 
+    if (dest_is_slice) {
+        const operand_elem_size = operand_elem_ty.abiSize(target);
+        const dest_elem_size = dest_elem_ty.abiSize(target);
+        if (operand_elem_size != dest_elem_size) {
+            // note that this is not implemented in stage1 so we should probably wait
+            // until that codebase is replaced before implementing this in stage2.
+            return sema.fail(block, dest_ty_src, "TODO: implement @ptrCast between slices changing the length", .{});
+        }
+    }
+
     return sema.coerceCompatiblePtrs(block, aligned_dest_ty, ptr, operand_src);
 }
 
@@ -15743,7 +15759,7 @@ fn zirMinMax(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
-    air_tag: Air.Inst.Tag,
+    comptime air_tag: Air.Inst.Tag,
 ) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[inst].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
@@ -15763,7 +15779,7 @@ fn analyzeMinMax(
     src: LazySrcLoc,
     lhs: Air.Inst.Ref,
     rhs: Air.Inst.Ref,
-    air_tag: Air.Inst.Tag,
+    comptime air_tag: Air.Inst.Tag,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
@@ -20976,7 +20992,7 @@ fn resolvePeerTypes(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
-    instructions: []Air.Inst.Ref,
+    instructions: []const Air.Inst.Ref,
     candidate_srcs: Module.PeerTypeCandidateSrc,
 ) !Type {
     switch (instructions.len) {
@@ -22794,7 +22810,7 @@ pub fn addExtraAssumeCapacity(sema: *Sema, extra: anytype) u32 {
 }
 
 fn appendRefsAssumeCapacity(sema: *Sema, refs: []const Air.Inst.Ref) void {
-    const coerced = @bitCast([]const u32, refs);
+    const coerced = @ptrCast([]const u32, refs);
     sema.air_extra.appendSliceAssumeCapacity(coerced);
 }
 
src/type.zig
@@ -1451,7 +1451,7 @@ pub const Type = extern union {
                 var duped_names = Module.ErrorSet.NameMap{};
                 try duped_names.ensureTotalCapacity(allocator, names.len);
                 for (names) |name| {
-                    duped_names.putAssumeCapacityNoClobber(name, .{});
+                    duped_names.putAssumeCapacityNoClobber(name, {});
                 }
                 return Tag.error_set_merged.create(allocator, duped_names);
             },
test/behavior/ptrcast.zig
@@ -217,3 +217,19 @@ test "implicit optional pointer to optional anyopaque pointer" {
     var z = @ptrCast(*[4]u8, y);
     try expect(std.mem.eql(u8, z, "aoeu"));
 }
+
+test "@ptrCast slice to slice" {
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
+
+    const S = struct {
+        fn foo(slice: []u32) []i32 {
+            return @ptrCast([]i32, slice);
+        }
+    };
+    var buf: [4]u32 = .{ 0, 0, 0, 0 };
+    const alias = S.foo(&buf);
+    alias[1] = 42;
+    try expect(buf[1] == 42);
+    try expect(alias.len == 4);
+}