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[DAG] foldCONCAT_VECTORS - fold concat_vectors(v1xX insertelt(v,e,0), ...) -> build_vector(e,...) #163420

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merged 2 commits into from
Oct 14, 2025
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[DAG] foldCONCAT_VECTORS - fold concat_vectors(v1xX insertelt(v,e,0), ...) -> build_vector(e,...) #163420

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[DAG] foldCONCAT_VECTORS - fold concat_vectors(v1xX insertelt(v,e,0),…
RKSimon Oct 14, 2025
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RKSimon Oct 14, 2025
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9 changes: 7 additions & 2 deletions llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6405,8 +6405,9 @@ static SDValue foldCONCAT_VECTORS(const SDLoc &DL, EVT VT,
if (VT.isScalableVector())
return SDValue();

// A CONCAT_VECTOR with all UNDEF/BUILD_VECTOR operands can be
// simplified to one big BUILD_VECTOR.
// A CONCAT_VECTOR of scalar sources, such as UNDEF, BUILD_VECTOR and
// single-element INSERT_VECTOR_ELT operands can be simplified to one big
// BUILD_VECTOR.
// FIXME: Add support for SCALAR_TO_VECTOR as well.
EVT SVT = VT.getScalarType();
SmallVector<SDValue, 16> Elts;
Expand All @@ -6416,6 +6417,10 @@ static SDValue foldCONCAT_VECTORS(const SDLoc &DL, EVT VT,
Elts.append(OpVT.getVectorNumElements(), DAG.getUNDEF(SVT));
else if (Op.getOpcode() == ISD::BUILD_VECTOR)
Elts.append(Op->op_begin(), Op->op_end());
else if (Op.getOpcode() == ISD::INSERT_VECTOR_ELT &&
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@topperc topperc Oct 14, 2025

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Update the comment above this loop?

OpVT.getVectorNumElements() == 1 &&
isNullConstant(Op.getOperand(2)))
Elts.push_back(Op.getOperand(1));
else
return SDValue();
}
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12 changes: 3 additions & 9 deletions llvm/test/CodeGen/X86/masked_gather_scatter.ll
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Expand Up @@ -4768,16 +4768,10 @@ declare void @llvm.masked.scatter.v8f32.v8p0(<8 x float>, <8 x ptr>, i32 immarg,
define <16 x i32> @pr163023(ptr %a0, <16 x i32> %a1) {
; X64-LABEL: pr163023:
; X64: # %bb.0:
; X64-NEXT: vpmovsxdq %ymm0, %zmm1
; X64-NEXT: vextracti64x4 $1, %zmm0, %ymm0
; X64-NEXT: vpmovsxdq %ymm0, %zmm0
; X64-NEXT: kxnorw %k0, %k0, %k1
; X64-NEXT: vpxor %xmm2, %xmm2, %xmm2
; X64-NEXT: vpxor %xmm3, %xmm3, %xmm3
; X64-NEXT: kxnorw %k0, %k0, %k2
; X64-NEXT: vpgatherqd (%rdi,%zmm0), %ymm3 {%k2}
; X64-NEXT: vpgatherqd (%rdi,%zmm1), %ymm2 {%k1}
; X64-NEXT: vinserti64x4 $1, %ymm3, %zmm2, %zmm0
; X64-NEXT: vpxor %xmm1, %xmm1, %xmm1
; X64-NEXT: vpgatherdd (%rdi,%zmm0), %zmm1 {%k1}
; X64-NEXT: vmovdqa64 %zmm1, %zmm0
; X64-NEXT: retq
;
; X86-LABEL: pr163023:
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