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[X86] isLoadBitCastBeneficial - its only beneficial to bitcast between vector types if the new type is legal #171813

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Merged
RKSimon merged 1 commit into from
Dec 11, 2025
Merged

[X86] isLoadBitCastBeneficial - its only beneficial to bitcast between vector types if the new type is legal #171813

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10 changes: 6 additions & 4 deletions llvm/lib/Target/X86/X86ISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3489,10 +3489,12 @@ bool X86TargetLowering::isLoadBitCastBeneficial(EVT LoadVT, EVT BitcastVT,
if (!Subtarget.hasDQI() && BitcastVT == MVT::v8i1 && LoadVT == MVT::i8)
return false;

// If both types are legal vectors, it's always ok to convert them.
if (LoadVT.isVector() && BitcastVT.isVector() &&
isTypeLegal(LoadVT) && isTypeLegal(BitcastVT))
return true;
if (LoadVT.isVector() && BitcastVT.isVector()) {
// If both types are legal vectors, it's always ok to convert them.
// Don't convert to an illegal type.
if (isTypeLegal(LoadVT))
return isTypeLegal(BitcastVT);
}

// If we have a large vector type (even if illegal), don't bitcast to large
// (illegal) scalar types. Better to load fewer vectors and extract.
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19 changes: 7 additions & 12 deletions llvm/test/CodeGen/X86/single_elt_vector_memory_operation.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -20,25 +20,22 @@ define void @load_single_128bit_elt_vector(ptr %in, ptr %off, ptr %out) nounwind
; AVX-LABEL: load_single_128bit_elt_vector:
; AVX: # %bb.0:
; AVX-NEXT: vmovaps (%rdi), %xmm0
; AVX-NEXT: vxorps %xmm1, %xmm1, %xmm1
; AVX-NEXT: vmovaps %xmm1, 16(%rdx)
; AVX-NEXT: vmovaps %xmm0, (%rdx)
; AVX-NEXT: vmovaps %ymm0, (%rdx)
; AVX-NEXT: vzeroupper
; AVX-NEXT: retq
;
; AVX2-LABEL: load_single_128bit_elt_vector:
; AVX2: # %bb.0:
; AVX2-NEXT: vmovaps (%rdi), %xmm0
; AVX2-NEXT: vxorps %xmm1, %xmm1, %xmm1
; AVX2-NEXT: vmovaps %xmm1, 16(%rdx)
; AVX2-NEXT: vmovaps %xmm0, (%rdx)
; AVX2-NEXT: vmovaps %ymm0, (%rdx)
; AVX2-NEXT: vzeroupper
; AVX2-NEXT: retq
;
; AVX512F-LABEL: load_single_128bit_elt_vector:
; AVX512F: # %bb.0:
; AVX512F-NEXT: vmovaps (%rdi), %xmm0
; AVX512F-NEXT: vxorps %xmm1, %xmm1, %xmm1
; AVX512F-NEXT: vmovaps %xmm1, 16(%rdx)
; AVX512F-NEXT: vmovaps %xmm0, (%rdx)
; AVX512F-NEXT: vmovaps %ymm0, (%rdx)
; AVX512F-NEXT: vzeroupper
; AVX512F-NEXT: retq
%i0 = load <16 x i8>, ptr %in, align 64
%i1 = bitcast <16 x i8> %i0 to <1 x i128>
Expand Down Expand Up @@ -112,9 +109,7 @@ define void @load_single_256bit_elt_vector(ptr %in, ptr %off, ptr %out) nounwind
; AVX512F-LABEL: load_single_256bit_elt_vector:
; AVX512F: # %bb.0:
; AVX512F-NEXT: vmovaps (%rdi), %ymm0
; AVX512F-NEXT: vxorps %xmm1, %xmm1, %xmm1
; AVX512F-NEXT: vmovaps %ymm1, 32(%rdx)
; AVX512F-NEXT: vmovaps %ymm0, (%rdx)
; AVX512F-NEXT: vmovaps %zmm0, (%rdx)
; AVX512F-NEXT: vzeroupper
; AVX512F-NEXT: retq
%i0 = load <32 x i8>, ptr %in, align 64
Expand Down