Commit 767d2526918192da548d77970f97028dd62cf9d1 | zig

author	lg <abbix@riseup.net> 2026-08-16 04:06:29+02:00
committer	Andrew Kelley <andrew@ziglang.org> 2026-08-16 04:06:29+02:00
log	767d2526918192da548d77970f97028dd62cf9d1
tree	1db67badbd3d012afe390355526063b733c4484d
parent	f506a49142cdb8454c70acd662bf7e45289ddae2

llvm: don't scalarize bitcast vectors on LE (#36512)

`scalarize_bit_cast_vector_non_elementwise` was previously unconditionally
enabled on both big-endian and little-endian targets, which led to
suboptimal emitting of vector-to-integer bitcasts (https://zig.godbolt.org/z/qEG8zqfqn). This patch only
enables it on big-endian targets as the little-endian semantics match
the zig semantics.

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/36512

1 files changed, 13 insertions(+), 10 deletions(-)

src
- codegen
  - llvm.zig

src/codegen/llvm.zig+13-10

...	@@ -31,16 +31,19 @@ const bindings = if (build_options.have_llvm)	...	@@ -31,16 +31,19 @@ const bindings = if (build_options.have_llvm)
31	else	31	else
32	@compileError("LLVM unavailable");	32	@compileError("LLVM unavailable");
33		33
34	pub fn legalizeFeatures(_: const std.Target) ?const Air.Legalize.Features {	34	pub fn legalizeFeatures(target: const std.Target) ?const Air.Legalize.Features {
35	return comptime &.initMany(&.{	35	return switch (target.cpu.arch.endian()) {
36	.expand_int_from_float_safe,	36	inline else => \|endian\| comptime &.init(.{
37	.expand_int_from_float_optimized_safe,	37	.expand_int_from_float_safe = true,
38		38	.expand_int_from_float_optimized_safe = true,
39	.scalarize_bit_cast_array,	39
40	// Needed because LLVM's `bitcast` on vectors is endian-specific unless the source and dest	40	.scalarize_bit_cast_array = true,
41	// types are vectors with equal length (hence also with equal bits-per-element).	41	// LLVM's `bitcast` on vectors places element 0 in the least significant bits on
42	.scalarize_bit_cast_vector_non_elementwise,	42	// little-endian targets, which matches our semantics; but it does the opposite on
43	});	43	// big-endian targets, so in that case we need to scalarize.
		44	.scalarize_bit_cast_vector_non_elementwise = endian != .little,
		45	}),
		46	};
44	}	47	}
45		48
46	fn subArchName(target: *const std.Target, comptime family: std.Target.Cpu.Arch.Family, mappings: anytype) ?[]const u8 {	49	fn subArchName(target: *const std.Target, comptime family: std.Target.Cpu.Arch.Family, mappings: anytype) ?[]const u8 {