[PATCH] D23330: [DAGCombine] Avoid INSERT_SUBVECTOR reinsertions (PR28678)

[Simon Pilgrim via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: majnemer, mkuper, spatel, andreadb.
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If the input vector to INSERT_SUBVECTOR is another INSERT_SUBVECTOR, and this inserted subvector replaces the last insertion, then insert into the common source vector.

Repository:
  rL LLVM

https://reviews.llvm.org/D23330

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/X86/avx-intrinsics-fast-isel.ll
  test/CodeGen/X86/insertelement-zero.ll

Index: test/CodeGen/X86/insertelement-zero.ll
===================================================================
--- test/CodeGen/X86/insertelement-zero.ll
+++ test/CodeGen/X86/insertelement-zero.ll
@@ -587,7 +587,6 @@
 ; AVX1-NEXT:    vblendps {{.*#+}} ymm0 = ymm1[0,1,2,3],ymm0[4,5,6,7]
 ; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm1
 ; AVX1-NEXT:    vpinsrb $14, %eax, %xmm1, %xmm1
-; AVX1-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
 ; AVX1-NEXT:    vpinsrb $15, %eax, %xmm1, %xmm1
 ; AVX1-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
 ; AVX1-NEXT:    retq
@@ -601,7 +600,6 @@
 ; AVX2-NEXT:    vpblendd {{.*#+}} ymm0 = ymm1[0,1,2,3],ymm0[4,5,6,7]
 ; AVX2-NEXT:    vextracti128 $1, %ymm0, %xmm1
 ; AVX2-NEXT:    vpinsrb $14, %eax, %xmm1, %xmm1
-; AVX2-NEXT:    vinserti128 $1, %xmm1, %ymm0, %ymm0
 ; AVX2-NEXT:    vpinsrb $15, %eax, %xmm1, %xmm1
 ; AVX2-NEXT:    vinserti128 $1, %xmm1, %ymm0, %ymm0
 ; AVX2-NEXT:    retq
Index: test/CodeGen/X86/avx-intrinsics-fast-isel.ll
===================================================================
--- test/CodeGen/X86/avx-intrinsics-fast-isel.ll
+++ test/CodeGen/X86/avx-intrinsics-fast-isel.ll
@@ -1026,9 +1026,8 @@
 ; X32:       # BB#0:
 ; X32-NEXT:    vextractf128 $1, %ymm0, %xmm1
 ; X32-NEXT:    vpinsrd $2, {{[0-9]+}}(%esp), %xmm1, %xmm1
-; X32-NEXT:    vpinsrd $3, {{[0-9]+}}(%esp), %xmm1, %xmm2
+; X32-NEXT:    vpinsrd $3, {{[0-9]+}}(%esp), %xmm1, %xmm1
 ; X32-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
-; X32-NEXT:    vinsertf128 $1, %xmm2, %ymm0, %ymm0
 ; X32-NEXT:    retl
 ;
 ; X64-LABEL: test_mm256_insert_epi64:
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13802,19 +13802,25 @@
 }
 
 SDValue DAGCombiner::visitINSERT_SUBVECTOR(SDNode *N) {
+  EVT VT = N->getValueType(0);
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   SDValue N2 = N->getOperand(2);
 
+  // If the input vector is another INSERT_SUBVECTOR, and this insert replaces
+  // the last insertion, then insert into the common source vector.
+  if (N0.getOpcode() == ISD::INSERT_SUBVECTOR && N0.getOperand(2) == N2)
+    return DAG.getNode(ISD::INSERT_SUBVECTOR, SDLoc(N), VT, N0.getOperand(0),
+                       N1, N2);
+
   if (N0.getValueType() != N1.getValueType())
     return SDValue();
 
   // If the input vector is a concatenation, and the insert replaces
   // one of the halves, we can optimize into a single concat_vectors.
   if (N0.getOpcode() == ISD::CONCAT_VECTORS && N0->getNumOperands() == 2 &&
       N2.getOpcode() == ISD::Constant) {
     APInt InsIdx = cast<ConstantSDNode>(N2)->getAPIntValue();
-    EVT VT = N->getValueType(0);
 
     // Lower half: fold (insert_subvector (concat_vectors X, Y), Z) ->
     // (concat_vectors Z, Y)


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