[llvm] 225ee03 - [DAG] foldCONCAT_VECTORS - fold concat_vectors(v1xX insertelt(v,e,0), ...) -> build_vector(e,...) (#163420)

[via llvm-commits]

Author: Simon Pilgrim
Date: 2025-10-14T17:44:18Z
New Revision: 225ee03f41107449d270014676fd9842bd7e9266

URL: https://github.com/llvm/llvm-project/commit/225ee03f41107449d270014676fd9842bd7e9266
DIFF: https://github.com/llvm/llvm-project/commit/225ee03f41107449d270014676fd9842bd7e9266.diff

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

Extend the foldCONCAT_VECTORS BUILD_VECTOR construction to handle cases where the scalars have come from <1 x X> vector insertions

Fixes #163023

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    llvm/test/CodeGen/X86/masked_gather_scatter.ll

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 876066e968873..90edaf3ef5471 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -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;
@@ -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 &&
+             OpVT.getVectorNumElements() == 1 &&
+             isNullConstant(Op.getOperand(2)))
+      Elts.push_back(Op.getOperand(1));
     else
       return SDValue();
   }

diff  --git a/llvm/test/CodeGen/X86/masked_gather_scatter.ll b/llvm/test/CodeGen/X86/masked_gather_scatter.ll
index c658c40a2d636..cdf6bdd2ab184 100644
--- a/llvm/test/CodeGen/X86/masked_gather_scatter.ll
+++ b/llvm/test/CodeGen/X86/masked_gather_scatter.ll
@@ -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: