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codegen: fix taking the address of a zero-bit field in a zero-bit struct

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Normally when we want a pointer to the end of a struct we just add 1 to
the struct pointer.  However, when it is a zero-bit struct, the pointer
type being used during lowering is often a dummy pointer type that
actually points to a non-zero-bit type, so we actually want to add 0
instead, since a zero-bit struct begins and ends at the same address.
This commit is contained in:
Jacob Young 2022-12-18 22:09:13 -05:00
parent 52e5c66025
commit 0e3feebb04
3 changed files with 30 additions and 9 deletions
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4
src/codegen/c.zig
View File

@ -5131,7 +5131,9 @@ fn structFieldPtr(f: *Function, inst: Air.Inst.Index, struct_ptr_ty: Type, struc
.begin, .end => {
try writer.writeByte('(');
try f.writeCValue(writer, struct_ptr, .Other);
try writer.print(")[{}]", .{@boolToInt(field_loc == .end)});
try writer.print(")[{}]", .{
@boolToInt(field_loc == .end and struct_ty.hasRuntimeBitsIgnoreComptime()),
});
},
.field => |field| if (extra_name != .none) {
try f.writeCValueDerefMember(writer, struct_ptr, extra_name);

9
src/codegen/llvm.zig
View File

@ -4046,9 +4046,8 @@ pub const DeclGen = struct {
break :blk parent_llvm_ty.constInBoundsGEP(parent_llvm_ptr, &indices, indices.len);
} else {
bitcast_needed = !parent_ty.eql(ptr_child_ty, dg.module);
const indices: [1]*llvm.Value = .{
llvm_u32.constInt(1, .False),
};
const llvm_index = llvm_u32.constInt(@boolToInt(parent_ty.hasRuntimeBitsIgnoreComptime()), .False);
const indices: [1]*llvm.Value = .{llvm_index};
break :blk parent_llvm_ty.constInBoundsGEP(parent_llvm_ptr, &indices, indices.len);
}
},
@ -9774,8 +9773,8 @@ pub const FuncGen = struct {
// end of the struct. Treat our struct pointer as an array of two and get
// the index to the element at index `1` to get a pointer to the end of
// the struct.
const llvm_usize = try self.dg.lowerType(Type.usize);
const llvm_index = llvm_usize.constInt(1, .False);
const llvm_u32 = self.dg.context.intType(32);
const llvm_index = llvm_u32.constInt(@boolToInt(struct_ty.hasRuntimeBitsIgnoreComptime()), .False);
const indices: [1]*llvm.Value = .{llvm_index};
return self.builder.buildInBoundsGEP(struct_llvm_ty, struct_ptr, &indices, indices.len, "");
}

26
test/behavior/struct.zig
View File

@ -1365,7 +1365,7 @@ test "fieldParentPtr of a zero-bit field" {
if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
const S = struct {
fn testOneType(comptime A: type) !void {
fn testStruct(comptime A: type) !void {
{
const a = A{ .u = 0 };
const b_ptr = &a.b;
@ -1379,9 +1379,29 @@ test "fieldParentPtr of a zero-bit field" {
try std.testing.expectEqual(&a, a_ptr);
}
}
fn testNestedStruct(comptime A: type) !void {
{
const a = A{ .u = 0 };
const c_ptr = &a.b.c;
const b_ptr = @fieldParentPtr(@TypeOf(a.b), "c", c_ptr);
try std.testing.expectEqual(&a.b, b_ptr);
const a_ptr = @fieldParentPtr(A, "b", b_ptr);
try std.testing.expectEqual(&a, a_ptr);
}
{
var a = A{ .u = 0 };
const c_ptr = &a.b.c;
const b_ptr = @fieldParentPtr(@TypeOf(a.b), "c", c_ptr);
try std.testing.expectEqual(&a.b, b_ptr);
const a_ptr = @fieldParentPtr(A, "b", b_ptr);
try std.testing.expectEqual(&a, a_ptr);
}
}
fn doTheTest() !void {
try testOneType(struct { b: void = {}, u: u8 });
try testOneType(struct { u: u8, b: void = {} });
try testStruct(struct { b: void = {}, u: u8 });
try testStruct(struct { u: u8, b: void = {} });
try testNestedStruct(struct { b: struct { c: void = {} } = .{}, u: u8 });
try testNestedStruct(struct { u: u8, b: struct { c: void = {} } = .{} });
}
};
try S.doTheTest();