Commit ba6abd71c2d3664bc658cf5ce55b5c53052dc720 | zig

author	Matthew Lugg <mlugg@mlugg.co.uk> 2025-08-12 23:18:05+01:00
committer	Matthew Lugg <mlugg@mlugg.co.uk> 2025-08-13 11:36:16+01:00
log	ba6abd71c2d3664bc658cf5ce55b5c53052dc720
tree	116c178b6877cbf07abbeec681768adbaebd7449
parent	38ba425b26312ea073c7082e576e8583913139d7
signature	Commit is signed but in an unrecognized format.

llvm: unions which are equivalent to enums are not by-ref

The LLVM backend lowers unions where all fields are zero-bit as
equivalent to their backing enum, and expects them to have the same
by-ref-ness in at least one place in the backend, probably more.

Resolves: #23577

2 files changed, 16 insertions(+), 1 deletions(-)

src
- codegen
  - llvm.zig
test
- behavior
  - cast.zig

src/codegen/llvm.zig+1-1

...	@@ -12777,7 +12777,7 @@ fn isByRef(ty: Type, zcu: *Zcu) bool {	...	@@ -12777,7 +12777,7 @@ fn isByRef(ty: Type, zcu: *Zcu) bool {
12777	},	12777	},
12778	.@"union" => switch (ty.containerLayout(zcu)) {	12778	.@"union" => switch (ty.containerLayout(zcu)) {
12779	.@"packed" => return false,	12779	.@"packed" => return false,
12780	else => return ty.hasRuntimeBits(zcu),	12780	else => return ty.hasRuntimeBits(zcu) and !ty.unionHasAllZeroBitFieldTypes(zcu),
12781	},	12781	},
12782	.error_union => {	12782	.error_union => {
12783	const payload_ty = ty.errorUnionPayload(zcu);	12783	const payload_ty = ty.errorUnionPayload(zcu);

test/behavior/cast.zig+15

...	@@ -2722,3 +2722,18 @@ test "@intFromFloat vector boundary cases" {	...	@@ -2722,3 +2722,18 @@ test "@intFromFloat vector boundary cases" {
2722	try S.doTheTest();	2722	try S.doTheTest();
2723	try comptime S.doTheTest();	2723	try comptime S.doTheTest();
2724	}	2724	}
		2725
		2726	test "coerce enum to union with zero-bit fields through local variables" {
		2727	if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
		2728
		2729	const E = enum(u1) { foo, bar };
		2730	const U = union(E) { foo, bar };
		2731
		2732	var runtime: E = undefined;
		2733	runtime = .foo;
		2734
		2735	var result: U = undefined;
		2736	result = runtime;
		2737
		2738	try expect(result == .foo);
		2739	}