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Rollup merge of #118864 - farnoy:masked-load-store-fixes, r=workingju…
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Fix alignment passed down to LLVM for simd_masked_load

Follow up to #117953

The alignment for a masked load operation should be that of the element/lane, not the vector as a whole

It can produce miscompilations after the LLVM optimizer notices the higher alignment and promotes this to an unmasked, aligned load followed up by blend/select - https://rust.godbolt.org/z/KEeGbevbb
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workingjubilee authored Dec 13, 2023
2 parents 2d1d443 + 95b5a80 commit a33f1a3
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Showing 3 changed files with 3 additions and 3 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_codegen_llvm/src/intrinsic.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1568,7 +1568,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(

// Alignment of T, must be a constant integer value:
let alignment_ty = bx.type_i32();
let alignment = bx.const_i32(bx.align_of(values_ty).bytes() as i32);
let alignment = bx.const_i32(bx.align_of(values_elem).bytes() as i32);

// Truncate the mask vector to a vector of i1s:
let (mask, mask_ty) = {
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@ extern "platform-intrinsic" {
#[no_mangle]
pub unsafe fn load_f32x2(mask: Vec2<i32>, pointer: *const f32,
values: Vec2<f32>) -> Vec2<f32> {
// CHECK: call <2 x float> @llvm.masked.load.v2f32.p0(ptr {{.*}}, i32 {{.*}}, <2 x i1> {{.*}}, <2 x float> {{.*}})
// CHECK: call <2 x float> @llvm.masked.load.v2f32.p0(ptr {{.*}}, i32 4, <2 x i1> {{.*}}, <2 x float> {{.*}})
simd_masked_load(mask, pointer, values)
}

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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ extern "platform-intrinsic" {
// CHECK-LABEL: @store_f32x2
#[no_mangle]
pub unsafe fn store_f32x2(mask: Vec2<i32>, pointer: *mut f32, values: Vec2<f32>) {
// CHECK: call void @llvm.masked.store.v2f32.p0(<2 x float> {{.*}}, ptr {{.*}}, i32 {{.*}}, <2 x i1> {{.*}})
// CHECK: call void @llvm.masked.store.v2f32.p0(<2 x float> {{.*}}, ptr {{.*}}, i32 4, <2 x i1> {{.*}})
simd_masked_store(mask, pointer, values)
}

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