| author |  Ryan Mehri <ryan.mehri1@gmail.com> 2026-08-04 11:43:46-04:00 |
| committer |  Matthew Lugg <mlugg@mlugg.co.uk> 2026-08-07 15:29:04+02:00 |
| log | b9852d23089a524dafaa2487f207457b2a183af1 |
| tree | 6f39d844db264505e301b12eb6fabc405fee702f |
| parent | 17e07ffc6381a1650b6bac5948b9f22d24411982 |
Legalize: fix packed struct with OPV and multiple other fields
In legalization for packed struct init with an OPV field, we first try
to see if any field accounts for the entire bit size of the struct and
otherwise fall back to a sequence of bitcasts and shifts on each field
(added in fc1c83a363d). However, OPV fields are not accounted for
in the fallback case, which means that codegen eventually panics when
seeing the bit size of 0.
This change makes it so that we ignore all OPV fields in
`packedAggregateInitBlockPayload` since they have no runtime bits.2 files changed, 24 insertions(+), 1 deletions(-)
src- Air
- test
- behavior
src/Air/Legalize.zig+8-1
| ... | ... | @@ -2906,12 +2906,18 @@ fn packedAggregateInitBlockPayload(l: *Legalize, orig_inst: Air.Inst.Index) Erro |
| 2906 | 2906 | const orig_ty_pl = l.air_instructions.items(.data)[@backingInt(orig_inst)].ty_pl; |
| 2907 | 2907 | const agg_ty = orig_ty_pl.ty.toType(); |
| 2908 | 2908 | const agg_field_count = agg_ty.structFieldCount(zcu); |
| 2909 | var opv_field_count: u32 = 0; | |
| 2910 | for (0..agg_field_count) |field_idx| { | |
| 2911 | const field_ty = agg_ty.fieldType(field_idx, zcu); | |
| 2912 | const field_bits: u16 = @intCast(field_ty.bitSize(zcu)); | |
| 2913 | if (field_bits == 0) opv_field_count += 1; | |
| 2914 | } | |
| 2909 | 2915 | |
| 2910 | 2916 | var bfa_buf: [4 * 32 + 2]Air.Inst.Index = undefined; |
| 2911 | 2917 | var bfa_state: std.heap.BufferFirstAllocator = .init(@ptrCast(&bfa_buf), gpa); |
| 2912 | 2918 | const bfa = bfa_state.allocator(); |
| 2913 | 2919 | |
| 2914 | const inst_buf = try bfa.alloc(Air.Inst.Index, 4 * agg_field_count + 2); | |
| 2920 | const inst_buf = try bfa.alloc(Air.Inst.Index, 4 * (agg_field_count - opv_field_count) + 2); | |
| 2915 | 2921 | defer bfa.free(inst_buf); |
| 2916 | 2922 | |
| 2917 | 2923 | var main_block: Block = .init(inst_buf); |
| ... | ... | @@ -2927,6 +2933,7 @@ fn packedAggregateInitBlockPayload(l: *Legalize, orig_inst: Air.Inst.Index) Erro |
| 2927 | 2933 | field_idx -= 1; |
| 2928 | 2934 | const field_ty = agg_ty.fieldType(field_idx, zcu); |
| 2929 | 2935 | const field_bits: u16 = @intCast(field_ty.bitSize(zcu)); |
| 2936 | if (field_bits == 0) continue; | |
| 2930 | 2937 | assert(field_bits < num_bits); |
| 2931 | 2938 | const field_uint_ty = try pt.intType(.unsigned, field_bits); |
| 2932 | 2939 | const field_bit_size_ref: Air.Inst.Ref = .fromValue(try pt.intValue(shift_ty, field_bits)); |
test/behavior/bitcast.zig+16
| ... | ... | @@ -432,6 +432,22 @@ test "@bitCast of packed struct with void field to integer" { |
| 432 | 432 | try comptime S.doTheTest(123); |
| 433 | 433 | } |
| 434 | 434 | |
| 435 | test "@bitCast of packed struct with void field and multiple integers" { | |
| 436 | const S = packed struct { | |
| 437 | x: u8, | |
| 438 | v: void, | |
| 439 | y: u8, | |
| 440 | ||
| 441 | fn doTheTest(x: u8, y: u8) !void { | |
| 442 | const foo = @as(@This(), .{ .x = x, .v = {}, .y = y }); | |
| 443 | const as_int: u16 = @bitCast(foo); | |
| 444 | try expect(as_int == @as(u16, y) << 8 | x); | |
| 445 | } | |
| 446 | }; | |
| 447 | try S.doTheTest(123, 45); | |
| 448 | try comptime S.doTheTest(123, 45); | |
| 449 | } | |
| 450 | ||
| 435 | 451 | test "@bitCast vector to array with different element size" { |
| 436 | 452 | if (builtin.zig_backend == .stage2_spirv) return error.SkipZigTest; |
| 437 | 453 |