Commit 6afcaf4a08

Andrew Kelley <andrew@ziglang.org>
2021-11-22 03:39:32
stage2: fix the build for 32-bit architectures
* Introduce a mechanism into Sema for emitting a compile error when an integer is too big and we need it to fit into a usize. * Add `@intCast` where necessary * link/MachO: fix an unnecessary allocation when all that was happening was appending zeroes to an ArrayList. * Add `error.Overflow` as a possible error to some codepaths, allowing usage of `math.intCast`. closes #9710
1 parent 96e5f66
src/arch/wasm/CodeGen.zig
@@ -538,6 +538,8 @@ const InnerError = error{
     AnalysisFail,
     /// Failed to emit MIR instructions to binary/textual representation.
     EmitFail,
+    /// Compiler implementation could not handle a large integer.
+    Overflow,
 };
 
 pub fn deinit(self: *Self) void {
@@ -877,7 +879,8 @@ pub fn gen(self: *Self, ty: Type, val: Value) InnerError!Result {
         },
         .Struct => {
             // TODO write the fields for real
-            try self.code.writer().writeByteNTimes(0xaa, ty.abiSize(self.target));
+            const abi_size = try std.math.cast(usize, ty.abiSize(self.target));
+            try self.code.writer().writeByteNTimes(0xaa, abi_size);
             return Result{ .appended = {} };
         },
         else => |tag| return self.fail("TODO: Implement zig type codegen for type: '{s}'", .{tag}),
src/arch/x86_64/abi.zig
@@ -207,7 +207,7 @@ pub fn classifySystemV(ty: Type, target: Target) [8]Class {
                         // "Otherwise class SSE is used."
                         result[result_i] = .sse;
                     }
-                    byte_i += field_size;
+                    byte_i += @intCast(usize, field_size);
                     if (byte_i == 8) {
                         byte_i = 0;
                         result_i += 1;
@@ -222,7 +222,7 @@ pub fn classifySystemV(ty: Type, target: Target) [8]Class {
                     result_i += field_class.len;
                     // If there are any bytes leftover, we have to try to combine
                     // the next field with them.
-                    byte_i = field_size % 8;
+                    byte_i = @intCast(usize, field_size % 8);
                     if (byte_i != 0) result_i -= 1;
                 }
             }
src/arch/x86_64/Emit.zig
@@ -42,6 +42,7 @@ relocs: std.ArrayListUnmanaged(Reloc) = .{},
 
 const InnerError = error{
     OutOfMemory,
+    Overflow,
     EmitFail,
 };
 
@@ -174,10 +175,11 @@ fn fixupRelocs(emit: *Emit) InnerError!void {
     // possible resolution, i.e., 8bit, and iteratively converge on the minimum required resolution
     // until the entire decl is correctly emitted with all JMP/CALL instructions within range.
     for (emit.relocs.items) |reloc| {
+        const offset = try math.cast(usize, reloc.offset);
         const target = emit.code_offset_mapping.get(reloc.target) orelse
             return emit.fail("JMP/CALL relocation target not found!", .{});
         const disp = @intCast(i32, @intCast(i64, target) - @intCast(i64, reloc.source + reloc.length));
-        mem.writeIntLittle(i32, emit.code.items[reloc.offset..][0..4], disp);
+        mem.writeIntLittle(i32, emit.code.items[offset..][0..4], disp);
     }
 }
 
src/codegen/llvm.zig
@@ -1006,10 +1006,18 @@ pub const DeclGen = struct {
                 const int_info = tv.ty.intInfo(target);
                 const llvm_type = self.context.intType(int_info.bits);
 
-                const unsigned_val = if (bigint.limbs.len == 1)
-                    llvm_type.constInt(bigint.limbs[0], .False)
-                else
-                    llvm_type.constIntOfArbitraryPrecision(@intCast(c_uint, bigint.limbs.len), bigint.limbs.ptr);
+                const unsigned_val = v: {
+                    if (bigint.limbs.len == 1) {
+                        break :v llvm_type.constInt(bigint.limbs[0], .False);
+                    }
+                    if (@sizeOf(usize) == @sizeOf(u64)) {
+                        break :v llvm_type.constIntOfArbitraryPrecision(
+                            @intCast(c_uint, bigint.limbs.len),
+                            bigint.limbs.ptr,
+                        );
+                    }
+                    @panic("TODO implement bigint to llvm int for 32-bit compiler builds");
+                };
                 if (!bigint.positive) {
                     return llvm.constNeg(unsigned_val);
                 }
@@ -1026,10 +1034,18 @@ pub const DeclGen = struct {
                 const int_info = tv.ty.intInfo(target);
                 const llvm_type = self.context.intType(int_info.bits);
 
-                const unsigned_val = if (bigint.limbs.len == 1)
-                    llvm_type.constInt(bigint.limbs[0], .False)
-                else
-                    llvm_type.constIntOfArbitraryPrecision(@intCast(c_uint, bigint.limbs.len), bigint.limbs.ptr);
+                const unsigned_val = v: {
+                    if (bigint.limbs.len == 1) {
+                        break :v llvm_type.constInt(bigint.limbs[0], .False);
+                    }
+                    if (@sizeOf(usize) == @sizeOf(u64)) {
+                        break :v llvm_type.constIntOfArbitraryPrecision(
+                            @intCast(c_uint, bigint.limbs.len),
+                            bigint.limbs.ptr,
+                        );
+                    }
+                    @panic("TODO implement bigint to llvm int for 32-bit compiler builds");
+                };
                 if (!bigint.positive) {
                     return llvm.constNeg(unsigned_val);
                 }
@@ -1144,7 +1160,7 @@ pub const DeclGen = struct {
                     const val = tv.val.castTag(.repeated).?.data;
                     const elem_ty = tv.ty.elemType();
                     const sentinel = tv.ty.sentinel();
-                    const len = tv.ty.arrayLen();
+                    const len = @intCast(usize, tv.ty.arrayLen());
                     const len_including_sent = len + @boolToInt(sentinel != null);
                     const gpa = self.gpa;
                     const llvm_elems = try gpa.alloc(*const llvm.Value, len_including_sent);
@@ -1317,7 +1333,7 @@ pub const DeclGen = struct {
                 .bytes => {
                     // Note, sentinel is not stored even if the type has a sentinel.
                     const bytes = tv.val.castTag(.bytes).?.data;
-                    const vector_len = tv.ty.arrayLen();
+                    const vector_len = @intCast(usize, tv.ty.arrayLen());
                     assert(vector_len == bytes.len or vector_len + 1 == bytes.len);
 
                     const elem_ty = tv.ty.elemType();
@@ -1343,7 +1359,7 @@ pub const DeclGen = struct {
                     // Note, sentinel is not stored even if the type has a sentinel.
                     // The value includes the sentinel in those cases.
                     const elem_vals = tv.val.castTag(.array).?.data;
-                    const vector_len = tv.ty.arrayLen();
+                    const vector_len = @intCast(usize, tv.ty.arrayLen());
                     assert(vector_len == elem_vals.len or vector_len + 1 == elem_vals.len);
                     const elem_ty = tv.ty.elemType();
                     const llvm_elems = try self.gpa.alloc(*const llvm.Value, vector_len);
@@ -1360,7 +1376,7 @@ pub const DeclGen = struct {
                     // Note, sentinel is not stored even if the type has a sentinel.
                     const val = tv.val.castTag(.repeated).?.data;
                     const elem_ty = tv.ty.elemType();
-                    const len = tv.ty.arrayLen();
+                    const len = @intCast(usize, tv.ty.arrayLen());
                     const llvm_elems = try self.gpa.alloc(*const llvm.Value, len);
                     defer self.gpa.free(llvm_elems);
                     for (llvm_elems) |*elem| {
src/link/MachO.zig
@@ -1788,19 +1788,18 @@ pub fn getMatchingSection(self: *MachO, sect: macho.section_64) !?MatchingSectio
 }
 
 pub fn createEmptyAtom(self: *MachO, local_sym_index: u32, size: u64, alignment: u32) !*Atom {
-    const code = try self.base.allocator.alloc(u8, size);
-    defer self.base.allocator.free(code);
-    mem.set(u8, code, 0);
-
+    const size_usize = try math.cast(usize, size);
     const atom = try self.base.allocator.create(Atom);
     errdefer self.base.allocator.destroy(atom);
     atom.* = Atom.empty;
     atom.local_sym_index = local_sym_index;
     atom.size = size;
     atom.alignment = alignment;
-    try atom.code.appendSlice(self.base.allocator, code);
-    try self.managed_atoms.append(self.base.allocator, atom);
 
+    try atom.code.resize(self.base.allocator, size_usize);
+    mem.set(u8, atom.code.items, 0);
+
+    try self.managed_atoms.append(self.base.allocator, atom);
     return atom;
 }
 
@@ -1872,9 +1871,10 @@ fn writeAtoms(self: *MachO) !void {
         while (true) {
             if (atom.dirty or self.invalidate_relocs) {
                 const atom_sym = self.locals.items[atom.local_sym_index];
-                const padding_size: u64 = if (atom.next) |next| blk: {
+                const padding_size: usize = if (atom.next) |next| blk: {
                     const next_sym = self.locals.items[next.local_sym_index];
-                    break :blk next_sym.n_value - (atom_sym.n_value + atom.size);
+                    const size = next_sym.n_value - (atom_sym.n_value + atom.size);
+                    break :blk try math.cast(usize, size);
                 } else 0;
 
                 log.debug("  (adding atom {s} to buffer: {})", .{ self.getString(atom_sym.n_strx), atom_sym });
src/link/Plan9.zig
@@ -71,9 +71,9 @@ entry_val: ?u64 = null,
 got_len: usize = 0,
 // A list of all the free got indexes, so when making a new decl
 // don't make a new one, just use one from here.
-got_index_free_list: std.ArrayListUnmanaged(u64) = .{},
+got_index_free_list: std.ArrayListUnmanaged(usize) = .{},
 
-syms_index_free_list: std.ArrayListUnmanaged(u64) = .{},
+syms_index_free_list: std.ArrayListUnmanaged(usize) = .{},
 
 const Bases = struct {
     text: u64,
@@ -356,8 +356,8 @@ pub fn changeLine(l: *std.ArrayList(u8), delta_line: i32) !void {
     }
 }
 
-fn declCount(self: *Plan9) u64 {
-    var fn_decl_count: u64 = 0;
+fn declCount(self: *Plan9) usize {
+    var fn_decl_count: usize = 0;
     var itf_files = self.fn_decl_table.iterator();
     while (itf_files.next()) |ent| {
         // get the submap
src/codegen.zig
@@ -37,6 +37,7 @@ pub const Result = union(enum) {
 
 pub const GenerateSymbolError = error{
     OutOfMemory,
+    Overflow,
     /// A Decl that this symbol depends on had a semantic analysis failure.
     AnalysisFail,
 };
@@ -289,7 +290,8 @@ pub fn generateSymbol(
             const field_vals = typed_value.val.castTag(.@"struct").?.data;
             _ = field_vals; // TODO write the fields for real
             const target = bin_file.options.target;
-            try code.writer().writeByteNTimes(0xaa, typed_value.ty.abiSize(target));
+            const abi_size = try math.cast(usize, typed_value.ty.abiSize(target));
+            try code.writer().writeByteNTimes(0xaa, abi_size);
             return Result{ .appended = {} };
         },
         else => |t| {
src/link.zig
@@ -350,9 +350,39 @@ pub const File = struct {
         }
     }
 
+    pub const UpdateDeclError = error{
+        OutOfMemory,
+        Overflow,
+        Underflow,
+        FileTooBig,
+        InputOutput,
+        FilesOpenedWithWrongFlags,
+        IsDir,
+        NoSpaceLeft,
+        Unseekable,
+        PermissionDenied,
+        FileBusy,
+        SystemResources,
+        OperationAborted,
+        BrokenPipe,
+        ConnectionResetByPeer,
+        ConnectionTimedOut,
+        NotOpenForReading,
+        WouldBlock,
+        AccessDenied,
+        Unexpected,
+        DiskQuota,
+        NotOpenForWriting,
+        AnalysisFail,
+        CodegenFail,
+        EmitFail,
+        NameTooLong,
+        CurrentWorkingDirectoryUnlinked,
+    };
+
     /// May be called before or after updateDeclExports but must be called
     /// after allocateDeclIndexes for any given Decl.
-    pub fn updateDecl(base: *File, module: *Module, decl: *Module.Decl) !void {
+    pub fn updateDecl(base: *File, module: *Module, decl: *Module.Decl) UpdateDeclError!void {
         log.debug("updateDecl {*} ({s}), type={}", .{ decl, decl.name, decl.ty });
         assert(decl.has_tv);
         switch (base.tag) {
@@ -370,7 +400,7 @@ pub const File = struct {
 
     /// May be called before or after updateDeclExports but must be called
     /// after allocateDeclIndexes for any given Decl.
-    pub fn updateFunc(base: *File, module: *Module, func: *Module.Fn, air: Air, liveness: Liveness) !void {
+    pub fn updateFunc(base: *File, module: *Module, func: *Module.Fn, air: Air, liveness: Liveness) UpdateDeclError!void {
         log.debug("updateFunc {*} ({s}), type={}", .{
             func.owner_decl, func.owner_decl.name, func.owner_decl.ty,
         });
@@ -387,7 +417,7 @@ pub const File = struct {
         }
     }
 
-    pub fn updateDeclLineNumber(base: *File, module: *Module, decl: *Module.Decl) !void {
+    pub fn updateDeclLineNumber(base: *File, module: *Module, decl: *Module.Decl) UpdateDeclError!void {
         log.debug("updateDeclLineNumber {*} ({s}), line={}", .{
             decl, decl.name, decl.src_line + 1,
         });
@@ -407,12 +437,17 @@ pub const File = struct {
     /// TODO we're transitioning to deleting this function and instead having
     /// each linker backend notice the first time updateDecl or updateFunc is called, or
     /// a callee referenced from AIR.
-    pub fn allocateDeclIndexes(base: *File, decl: *Module.Decl) !void {
+    pub fn allocateDeclIndexes(base: *File, decl: *Module.Decl) error{OutOfMemory}!void {
         log.debug("allocateDeclIndexes {*} ({s})", .{ decl, decl.name });
         switch (base.tag) {
             .coff => return @fieldParentPtr(Coff, "base", base).allocateDeclIndexes(decl),
             .elf => return @fieldParentPtr(Elf, "base", base).allocateDeclIndexes(decl),
-            .macho => return @fieldParentPtr(MachO, "base", base).allocateDeclIndexes(decl),
+            .macho => return @fieldParentPtr(MachO, "base", base).allocateDeclIndexes(decl) catch |err| switch (err) {
+                // remap this error code because we are transitioning away from
+                // `allocateDeclIndexes`.
+                error.Overflow => return error.OutOfMemory,
+                error.OutOfMemory => return error.OutOfMemory,
+            },
             .wasm => return @fieldParentPtr(Wasm, "base", base).allocateDeclIndexes(decl),
             .plan9 => return @fieldParentPtr(Plan9, "base", base).allocateDeclIndexes(decl),
             .c, .spirv => {},
src/Module.zig
@@ -3661,7 +3661,8 @@ pub fn embedFile(mod: *Module, cur_file: *File, rel_file_path: []const u8) !*Emb
     defer file.close();
 
     const stat = try file.stat();
-    const bytes = try file.readToEndAllocOptions(gpa, std.math.maxInt(u32), stat.size, 1, 0);
+    const size_usize = try std.math.cast(usize, stat.size);
+    const bytes = try file.readToEndAllocOptions(gpa, std.math.maxInt(u32), size_usize, 1, 0);
 
     log.debug("new embedFile. resolved_root_path={s}, resolved_path={s}, sub_file_path={s}, rel_file_path={s}", .{
         resolved_root_path, resolved_path, sub_file_path, rel_file_path,
@@ -3694,7 +3695,8 @@ pub fn detectEmbedFileUpdate(mod: *Module, embed_file: *EmbedFile) !void {
     if (unchanged_metadata) return;
 
     const gpa = mod.gpa;
-    const bytes = try file.readToEndAllocOptions(gpa, std.math.maxInt(u32), stat.size, 1, 0);
+    const size_usize = try std.math.cast(usize, stat.size);
+    const bytes = try file.readToEndAllocOptions(gpa, std.math.maxInt(u32), size_usize, 1, 0);
     gpa.free(embed_file.bytes);
     embed_file.bytes = bytes;
     embed_file.stat_size = stat.size;
src/Sema.zig
@@ -7020,7 +7020,7 @@ fn zirBitNot(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.
         if (val.isUndef()) {
             return sema.addConstUndef(scalar_type);
         } else if (operand_type.zigTypeTag() == .Vector) {
-            const vec_len = operand_type.arrayLen();
+            const vec_len = try sema.usizeCast(block, operand_src, operand_type.arrayLen());
             var elem_val_buf: Value.ElemValueBuffer = undefined;
             const elems = try sema.arena.alloc(Value, vec_len);
             for (elems) |*elem, i| {
@@ -7073,7 +7073,9 @@ fn zirArrayCat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
 
     if (try sema.resolveDefinedValue(block, lhs_src, lhs)) |lhs_val| {
         if (try sema.resolveDefinedValue(block, rhs_src, rhs)) |rhs_val| {
-            const final_len = lhs_info.len + rhs_info.len;
+            const lhs_len = try sema.usizeCast(block, lhs_src, lhs_info.len);
+            const rhs_len = try sema.usizeCast(block, lhs_src, rhs_info.len);
+            const final_len = lhs_len + rhs_len;
             const final_len_including_sent = final_len + @boolToInt(res_sent != null);
             const is_pointer = lhs_ty.zigTypeTag() == .Pointer;
             const lhs_sub_val = if (is_pointer) (try sema.pointerDeref(block, lhs_src, lhs_val, lhs_ty)).? else lhs_val;
@@ -7083,17 +7085,17 @@ fn zirArrayCat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
 
             const buf = try anon_decl.arena().alloc(Value, final_len_including_sent);
             {
-                var i: u64 = 0;
-                while (i < lhs_info.len) : (i += 1) {
+                var i: usize = 0;
+                while (i < lhs_len) : (i += 1) {
                     const val = try lhs_sub_val.elemValue(sema.arena, i);
                     buf[i] = try val.copy(anon_decl.arena());
                 }
             }
             {
-                var i: u64 = 0;
-                while (i < rhs_info.len) : (i += 1) {
+                var i: usize = 0;
+                while (i < rhs_len) : (i += 1) {
                     const val = try rhs_sub_val.elemValue(sema.arena, i);
-                    buf[lhs_info.len + i] = try val.copy(anon_decl.arena());
+                    buf[lhs_len + i] = try val.copy(anon_decl.arena());
                 }
             }
             const ty = if (res_sent) |rs| ty: {
@@ -7143,6 +7145,7 @@ fn zirArrayMul(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = sema.resolveInst(extra.lhs);
     const lhs_ty = sema.typeOf(lhs);
+    const src: LazySrcLoc = inst_data.src();
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
 
@@ -7151,11 +7154,14 @@ fn zirArrayMul(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
     const mulinfo = getArrayCatInfo(lhs_ty) orelse
         return sema.fail(block, lhs_src, "expected array, found '{}'", .{lhs_ty});
 
-    const final_len = std.math.mul(u64, mulinfo.len, factor) catch
+    const final_len_u64 = std.math.mul(u64, mulinfo.len, factor) catch
         return sema.fail(block, rhs_src, "operation results in overflow", .{});
-    const final_len_including_sent = final_len + @boolToInt(mulinfo.sentinel != null);
 
     if (try sema.resolveDefinedValue(block, lhs_src, lhs)) |lhs_val| {
+        const final_len = try sema.usizeCast(block, src, final_len_u64);
+        const final_len_including_sent = final_len + @boolToInt(mulinfo.sentinel != null);
+        const lhs_len = try sema.usizeCast(block, lhs_src, mulinfo.len);
+
         const lhs_sub_val = if (lhs_ty.zigTypeTag() == .Pointer) (try sema.pointerDeref(block, lhs_src, lhs_val, lhs_ty)).? else lhs_val;
 
         var anon_decl = try block.startAnonDecl();
@@ -7176,18 +7182,18 @@ fn zirArrayMul(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
 
         // Optimization for the common pattern of a single element repeated N times, such
         // as zero-filling a byte array.
-        const val = if (mulinfo.len == 1) blk: {
+        const val = if (lhs_len == 1) blk: {
             const elem_val = try lhs_sub_val.elemValue(sema.arena, 0);
             const copied_val = try elem_val.copy(anon_decl.arena());
             break :blk try Value.Tag.repeated.create(anon_decl.arena(), copied_val);
         } else blk: {
             // the actual loop
-            var i: u64 = 0;
+            var i: usize = 0;
             while (i < factor) : (i += 1) {
-                var j: u64 = 0;
-                while (j < mulinfo.len) : (j += 1) {
+                var j: usize = 0;
+                while (j < lhs_len) : (j += 1) {
                     const val = try lhs_sub_val.elemValue(sema.arena, j);
-                    buf[mulinfo.len * i + j] = try val.copy(anon_decl.arena());
+                    buf[lhs_len * i + j] = try val.copy(anon_decl.arena());
                 }
             }
             if (mulinfo.sentinel) |sent| {
@@ -8122,7 +8128,7 @@ fn analyzePtrArithmetic(
                     return sema.addConstUndef(new_ptr_ty);
                 }
 
-                const offset_int = offset_val.toUnsignedInt();
+                const offset_int = try sema.usizeCast(block, offset_src, offset_val.toUnsignedInt());
                 if (ptr_val.getUnsignedInt()) |addr| {
                     const target = sema.mod.getTarget();
                     const ptr_child_ty = ptr_ty.childType();
@@ -10204,7 +10210,7 @@ fn checkComptimeVarStore(
 }
 
 const SimdBinOp = struct {
-    len: ?u64,
+    len: ?usize,
     /// Coerced to `result_ty`.
     lhs: Air.Inst.Ref,
     /// Coerced to `result_ty`.
@@ -10230,7 +10236,7 @@ fn checkSimdBinOp(
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison();
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison();
 
-    var vec_len: ?u64 = null;
+    var vec_len: ?usize = null;
     if (lhs_zig_ty_tag == .Vector and rhs_zig_ty_tag == .Vector) {
         const lhs_len = lhs_ty.arrayLen();
         const rhs_len = rhs_ty.arrayLen();
@@ -10244,7 +10250,7 @@ fn checkSimdBinOp(
             };
             return sema.failWithOwnedErrorMsg(msg);
         }
-        vec_len = lhs_len;
+        vec_len = try sema.usizeCast(block, lhs_src, lhs_len);
     } else if (lhs_zig_ty_tag == .Vector or rhs_zig_ty_tag == .Vector) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "mixed scalar and vector operands: {} and {}", .{
@@ -12671,8 +12677,7 @@ fn storePtrVal(
     var kit = try beginComptimePtrMutation(sema, block, src, ptr_val);
     try sema.checkComptimeVarStore(block, src, kit.decl_ref_mut);
 
-    const target = sema.mod.getTarget();
-    const bitcasted_val = try operand_val.bitCast(operand_ty, kit.ty, target, sema.gpa, sema.arena);
+    const bitcasted_val = try sema.bitCastVal(block, src, operand_val, operand_ty, kit.ty);
 
     const arena = kit.beginArena(sema.gpa);
     defer kit.finishArena();
@@ -12724,7 +12729,9 @@ fn beginComptimePtrMutation(
                     const arena = parent.beginArena(sema.gpa);
                     defer parent.finishArena();
 
-                    const elems = try arena.alloc(Value, parent.ty.arrayLenIncludingSentinel());
+                    const array_len_including_sentinel =
+                        try sema.usizeCast(block, src, parent.ty.arrayLenIncludingSentinel());
+                    const elems = try arena.alloc(Value, array_len_including_sentinel);
                     mem.set(Value, elems, Value.undef);
 
                     parent.val.* = try Value.Tag.array.create(arena, elems);
@@ -12771,7 +12778,9 @@ fn beginComptimePtrMutation(
                     defer parent.finishArena();
 
                     const repeated_val = try parent.val.castTag(.repeated).?.data.copy(arena);
-                    const elems = try arena.alloc(Value, parent.ty.arrayLenIncludingSentinel());
+                    const array_len_including_sentinel =
+                        try sema.usizeCast(block, src, parent.ty.arrayLenIncludingSentinel());
+                    const elems = try arena.alloc(Value, array_len_including_sentinel);
                     mem.set(Value, elems, repeated_val);
 
                     parent.val.* = try Value.Tag.array.create(arena, elems);
@@ -12925,7 +12934,7 @@ fn beginComptimePtrLoad(
                 .root_val = parent.root_val,
                 .val = try parent.val.elemValue(sema.arena, elem_ptr.index),
                 .ty = elem_ty,
-                .byte_offset = parent.byte_offset + elem_size * elem_ptr.index,
+                .byte_offset = try sema.usizeCast(block, src, parent.byte_offset + elem_size * elem_ptr.index),
                 .is_mutable = parent.is_mutable,
             };
         },
@@ -12939,7 +12948,7 @@ fn beginComptimePtrLoad(
                 .root_val = parent.root_val,
                 .val = try parent.val.fieldValue(sema.arena, field_index),
                 .ty = parent.ty.structFieldType(field_index),
-                .byte_offset = parent.byte_offset + field_offset,
+                .byte_offset = try sema.usizeCast(block, src, parent.byte_offset + field_offset),
                 .is_mutable = parent.is_mutable,
             };
         },
@@ -12990,15 +12999,34 @@ fn bitCast(
 ) CompileError!Air.Inst.Ref {
     // TODO validate the type size and other compile errors
     if (try sema.resolveMaybeUndefVal(block, inst_src, inst)) |val| {
-        const target = sema.mod.getTarget();
         const old_ty = sema.typeOf(inst);
-        const result_val = try val.bitCast(old_ty, dest_ty, target, sema.gpa, sema.arena);
+        const result_val = try sema.bitCastVal(block, inst_src, val, old_ty, dest_ty);
         return sema.addConstant(dest_ty, result_val);
     }
     try sema.requireRuntimeBlock(block, inst_src);
     return block.addBitCast(dest_ty, inst);
 }
 
+pub fn bitCastVal(
+    sema: *Sema,
+    block: *Block,
+    src: LazySrcLoc,
+    val: Value,
+    old_ty: Type,
+    new_ty: Type,
+) !Value {
+    if (old_ty.eql(new_ty)) return val;
+
+    // For types with well-defined memory layouts, we serialize them a byte buffer,
+    // then deserialize to the new type.
+    const target = sema.mod.getTarget();
+    const abi_size = try sema.usizeCast(block, src, old_ty.abiSize(target));
+    const buffer = try sema.gpa.alloc(u8, abi_size);
+    defer sema.gpa.free(buffer);
+    val.writeToMemory(old_ty, target, buffer);
+    return Value.readFromMemory(new_ty, target, buffer, sema.arena);
+}
+
 fn coerceArrayPtrToSlice(
     sema: *Sema,
     block: *Block,
@@ -15103,7 +15131,7 @@ fn pointerDeref(sema: *Sema, block: *Block, src: LazySrcLoc, ptr_val: Value, ptr
         // The Type it is stored as in the compiler has an ABI size greater or equal to
         // the ABI size of `load_ty`. We may perform the bitcast based on
         // `parent.val` alone (more efficient).
-        return try parent.val.bitCast(parent.ty, load_ty, target, sema.gpa, sema.arena);
+        return try sema.bitCastVal(block, src, parent.val, parent.ty, load_ty);
     }
 
     // The Type it is stored as in the compiler has an ABI size less than the ABI size
@@ -15111,3 +15139,11 @@ fn pointerDeref(sema: *Sema, block: *Block, src: LazySrcLoc, ptr_val: Value, ptr
     // and reinterpreted starting at `parent.byte_offset`.
     return sema.fail(block, src, "TODO: implement bitcast with index offset", .{});
 }
+
+/// Used to convert a u64 value to a usize value, emitting a compile error if the number
+/// is too big to fit.
+fn usizeCast(sema: *Sema, block: *Block, src: LazySrcLoc, int: u64) CompileError!usize {
+    return std.math.cast(usize, int) catch |err| switch (err) {
+        error.Overflow => return sema.fail(block, src, "expression produces integer value {d} which is too big for this compiler implementation to handle", .{int}),
+    };
+}
src/value.zig
@@ -995,24 +995,6 @@ pub const Value = extern union {
         };
     }
 
-    pub fn bitCast(
-        val: Value,
-        old_ty: Type,
-        new_ty: Type,
-        target: Target,
-        gpa: *Allocator,
-        arena: *Allocator,
-    ) !Value {
-        if (old_ty.eql(new_ty)) return val;
-
-        // For types with well-defined memory layouts, we serialize them a byte buffer,
-        // then deserialize to the new type.
-        const buffer = try gpa.alloc(u8, old_ty.abiSize(target));
-        defer gpa.free(buffer);
-        val.writeToMemory(old_ty, target, buffer);
-        return Value.readFromMemory(new_ty, target, buffer, arena);
-    }
-
     pub fn writeToMemory(val: Value, ty: Type, target: Target, buffer: []u8) void {
         switch (ty.zigTypeTag()) {
             .Int => {
@@ -1039,7 +1021,7 @@ pub const Value = extern union {
             .Array, .Vector => {
                 const len = ty.arrayLen();
                 const elem_ty = ty.childType();
-                const elem_size = elem_ty.abiSize(target);
+                const elem_size = @intCast(usize, elem_ty.abiSize(target));
                 var elem_i: usize = 0;
                 var elem_value_buf: ElemValueBuffer = undefined;
                 var buf_off: usize = 0;
@@ -2494,7 +2476,7 @@ pub const Value = extern union {
         // resorting to BigInt first.
         var lhs_space: Value.BigIntSpace = undefined;
         const lhs_bigint = lhs.toBigInt(&lhs_space);
-        const shift = rhs.toUnsignedInt();
+        const shift = @intCast(usize, rhs.toUnsignedInt());
         const limbs = try allocator.alloc(
             std.math.big.Limb,
             lhs_bigint.limbs.len + (shift / (@sizeOf(std.math.big.Limb) * 8)) + 1,
@@ -2521,7 +2503,7 @@ pub const Value = extern union {
 
         var lhs_space: Value.BigIntSpace = undefined;
         const lhs_bigint = lhs.toBigInt(&lhs_space);
-        const shift = rhs.toUnsignedInt();
+        const shift = @intCast(usize, rhs.toUnsignedInt());
         const limbs = try arena.alloc(
             std.math.big.Limb,
             std.math.big.int.calcTwosCompLimbCount(info.bits),
@@ -2540,7 +2522,7 @@ pub const Value = extern union {
         // resorting to BigInt first.
         var lhs_space: Value.BigIntSpace = undefined;
         const lhs_bigint = lhs.toBigInt(&lhs_space);
-        const shift = rhs.toUnsignedInt();
+        const shift = @intCast(usize, rhs.toUnsignedInt());
         const limbs = try allocator.alloc(
             std.math.big.Limb,
             lhs_bigint.limbs.len - (shift / (@sizeOf(std.math.big.Limb) * 8)),