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[VectorCombine] Add initial nodes to the Worklist in VectorCombine #149047

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davemgreen
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This tries to mirror how InstructionWorklist is used in InstCombine, adding the nodes initially to a list that is added in reverse order to the Worklist. The general order should be the same, the main advantage of this is that as node are initially processed, when altered the New and Old instructions are visited immediately, helping remove Old instructions as they are replaced, helping other combines work without hitting OneUse checks.

@davemgreen
[VectorCombine] Add initial nodes to the Worklist in VectorCombine
f13ab03 
This tries to mirror how InstructionWorklist is used in InstCombine, adding the
nodes initially to a list that is added in reverse order to the Worklist.  The
general order should be the same, the main advantage of this is that as node
are initially processed, when altered the New and Old instructions are visited
immediately, helping remove Old instructions as they are replaced, helping
other combines work without hitting OneUse checks.
@davemgreen davemgreen requested review from nikic, fhahn and RKSimon July 16, 2025 09:38
@llvmbot
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llvmbot commented Jul 16, 2025 •
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@llvm/pr-subscribers-vectorizers
@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-backend-risc-v

Author: David Green (davemgreen)

Changes

This tries to mirror how InstructionWorklist is used in InstCombine, adding the nodes initially to a list that is added in reverse order to the Worklist. The general order should be the same, the main advantage of this is that as node are initially processed, when altered the New and Old instructions are visited immediately, helping remove Old instructions as they are replaced, helping other combines work without hitting OneUse checks.

Patch is 55.44 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/149047.diff

13 Files Affected:

  • (modified) llvm/lib/Transforms/Vectorize/VectorCombine.cpp (+7-3)
  • (modified) llvm/test/Transforms/PhaseOrdering/X86/hadd.ll (+11-11)
  • (modified) llvm/test/Transforms/PhaseOrdering/X86/hsub.ll (+11-11)
  • (modified) llvm/test/Transforms/VectorCombine/AArch64/ext-extract.ll (+69-32)
  • (modified) llvm/test/Transforms/VectorCombine/AArch64/load-extractelement-scalarization.ll (+8-8)
  • (modified) llvm/test/Transforms/VectorCombine/AArch64/select-shuffle.ll (+15-31)
  • (modified) llvm/test/Transforms/VectorCombine/RISCV/load-widening.ll (+4-4)
  • (modified) llvm/test/Transforms/VectorCombine/X86/concat-boolmasks.ll (+15-49)
  • (modified) llvm/test/Transforms/VectorCombine/X86/extract-binop-inseltpoison.ll (+1-3)
  • (modified) llvm/test/Transforms/VectorCombine/X86/extract-binop.ll (+2-3)
  • (modified) llvm/test/Transforms/VectorCombine/X86/reduction-two-vecs-combine.ll (+8-8)
  • (modified) llvm/test/Transforms/VectorCombine/X86/select-shuffle.ll (+3-4)
  • (modified) llvm/test/Transforms/VectorCombine/pr88796.ll (+4-4)
diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index fe8d74c43dfdc..3c7101c9f3c0d 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -3803,18 +3803,22 @@ bool VectorCombine::run() {
     }
   };
 
+  SmallVector<Instruction*, 128> InstrsForInstructionWorklist;
   for (BasicBlock &BB : F) {
     // Ignore unreachable basic blocks.
     if (!DT.isReachableFromEntry(&BB))
       continue;
-    // Use early increment range so that we can erase instructions in loop.
-    for (Instruction &I : make_early_inc_range(BB)) {
+    for (Instruction &I : BB) {
       if (I.isDebugOrPseudoInst())
         continue;
-      FoldInst(I);
+      InstrsForInstructionWorklist.push_back(&I);
     }
   }
 
+  Worklist.reserve(InstrsForInstructionWorklist.size());
+  for (auto I : reverse(InstrsForInstructionWorklist))
+    Worklist.push(I);
+
   while (!Worklist.isEmpty()) {
     Instruction *I = Worklist.removeOne();
     if (!I)
diff --git a/llvm/test/Transforms/PhaseOrdering/X86/hadd.ll b/llvm/test/Transforms/PhaseOrdering/X86/hadd.ll
index 798df4cd4ff54..f85d46689ccb0 100644
--- a/llvm/test/Transforms/PhaseOrdering/X86/hadd.ll
+++ b/llvm/test/Transforms/PhaseOrdering/X86/hadd.ll
@@ -121,12 +121,12 @@ define <8 x i16> @add_v8i16_u1234567(<8 x i16> %a, <8 x i16> %b) {
 
 define <8 x i16> @add_v8i16_76u43210(<8 x i16> %a, <8 x i16> %b) {
 ; SSE2-LABEL: @add_v8i16_76u43210(
-; SSE2-NEXT:    [[SHIFT:%.*]] = shufflevector <8 x i16> [[A:%.*]], <8 x i16> poison, <8 x i32> <i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE2-NEXT:    [[TMP1:%.*]] = add <8 x i16> [[A]], [[SHIFT]]
 ; SSE2-NEXT:    [[SHIFT2:%.*]] = shufflevector <8 x i16> [[B:%.*]], <8 x i16> poison, <8 x i32> <i32 poison, i32 poison, i32 poison, i32 poison, i32 5, i32 poison, i32 poison, i32 poison>
 ; SSE2-NEXT:    [[TMP2:%.*]] = add <8 x i16> [[B]], [[SHIFT2]]
 ; SSE2-NEXT:    [[SHIFT3:%.*]] = shufflevector <8 x i16> [[B]], <8 x i16> poison, <8 x i32> <i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 6>
 ; SSE2-NEXT:    [[TMP3:%.*]] = add <8 x i16> [[SHIFT3]], [[B]]
+; SSE2-NEXT:    [[TMP7:%.*]] = shufflevector <8 x i16> [[A:%.*]], <8 x i16> poison, <8 x i32> <i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE2-NEXT:    [[TMP1:%.*]] = add <8 x i16> [[A]], [[TMP7]]
 ; SSE2-NEXT:    [[TMP4:%.*]] = shufflevector <8 x i16> [[A]], <8 x i16> [[B]], <8 x i32> <i32 2, i32 4, i32 6, i32 8, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE2-NEXT:    [[TMP5:%.*]] = shufflevector <8 x i16> [[A]], <8 x i16> [[B]], <8 x i32> <i32 3, i32 5, i32 7, i32 9, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE2-NEXT:    [[TMP6:%.*]] = add <8 x i16> [[TMP4]], [[TMP5]]
@@ -404,13 +404,13 @@ define <16 x i16> @add_v16i16_FEuCBA98765432u0(<16 x i16> %a, <16 x i16> %b) {
 ; SSE4-LABEL: @add_v16i16_FEuCBA98765432u0(
 ; SSE4-NEXT:    [[TMP2:%.*]] = shufflevector <16 x i16> [[A:%.*]], <16 x i16> [[B:%.*]], <16 x i32> <i32 1, i32 poison, i32 5, i32 7, i32 17, i32 19, i32 21, i32 23, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE4-NEXT:    [[TMP10:%.*]] = shufflevector <16 x i16> [[TMP2]], <16 x i16> [[A]], <16 x i32> <i32 0, i32 poison, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 25, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 0, i32 poison, i32 4, i32 6, i32 16, i32 18, i32 20, i32 22, i32 8, i32 poison, i32 11, i32 12, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <16 x i16> [[TMP10]], <16 x i16> [[A]], <16 x i32> <i32 0, i32 poison, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 poison, i32 26, i32 29, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 0, i32 poison, i32 4, i32 6, i32 16, i32 18, i32 20, i32 22, i32 8, i32 11, i32 12, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <16 x i16> [[TMP10]], <16 x i16> [[A]], <16 x i32> <i32 0, i32 poison, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 26, i32 29, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE4-NEXT:    [[TMP6:%.*]] = add <16 x i16> [[TMP4]], [[TMP5]]
-; SSE4-NEXT:    [[TMP7:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 14, i32 24, i32 28, i32 30, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE4-NEXT:    [[TMP8:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 15, i32 25, i32 29, i32 31, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP7:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 14, i32 24, i32 poison, i32 28, i32 30, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP8:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 15, i32 25, i32 poison, i32 29, i32 31, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE4-NEXT:    [[TMP9:%.*]] = add <16 x i16> [[TMP7]], [[TMP8]]
-; SSE4-NEXT:    [[RESULT:%.*]] = shufflevector <16 x i16> [[TMP9]], <16 x i16> [[TMP6]], <16 x i32> <i32 3, i32 2, i32 poison, i32 1, i32 0, i32 27, i32 26, i32 24, i32 23, i32 22, i32 21, i32 20, i32 19, i32 18, i32 poison, i32 16>
+; SSE4-NEXT:    [[RESULT:%.*]] = shufflevector <16 x i16> [[TMP9]], <16 x i16> [[TMP6]], <16 x i32> <i32 4, i32 3, i32 poison, i32 1, i32 0, i32 26, i32 25, i32 24, i32 23, i32 22, i32 21, i32 20, i32 19, i32 18, i32 poison, i32 16>
 ; SSE4-NEXT:    ret <16 x i16> [[RESULT]]
 ;
 ; AVX2-LABEL: @add_v16i16_FEuCBA98765432u0(
@@ -1183,14 +1183,14 @@ define <8 x float> @add_v8f32_76u43210(<8 x float> %a, <8 x float> %b) {
 ; SSE2-NEXT:    ret <8 x float> [[RESULT]]
 ;
 ; SSE4-LABEL: @add_v8f32_76u43210(
-; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <8 x float> [[B:%.*]], <8 x float> [[A:%.*]], <8 x i32> <i32 6, i32 5, i32 poison, i32 0, i32 14, i32 12, i32 10, i32 8>
-; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <8 x float> [[B]], <8 x float> [[A]], <8 x i32> <i32 7, i32 4, i32 poison, i32 1, i32 15, i32 13, i32 11, i32 9>
+; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <8 x float> [[A:%.*]], <8 x float> [[B:%.*]], <8 x i32> <i32 14, i32 13, i32 poison, i32 8, i32 6, i32 4, i32 2, i32 0>
+; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <8 x float> [[A]], <8 x float> [[B]], <8 x i32> <i32 15, i32 12, i32 poison, i32 9, i32 7, i32 5, i32 3, i32 1>
 ; SSE4-NEXT:    [[TMP6:%.*]] = fadd <8 x float> [[TMP4]], [[TMP5]]
 ; SSE4-NEXT:    ret <8 x float> [[TMP6]]
 ;
 ; AVX-LABEL: @add_v8f32_76u43210(
-; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <8 x float> [[B:%.*]], <8 x float> [[A:%.*]], <8 x i32> <i32 6, i32 5, i32 poison, i32 0, i32 14, i32 12, i32 10, i32 8>
-; AVX-NEXT:    [[TMP2:%.*]] = shufflevector <8 x float> [[B]], <8 x float> [[A]], <8 x i32> <i32 7, i32 4, i32 poison, i32 1, i32 15, i32 13, i32 11, i32 9>
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <8 x float> [[A:%.*]], <8 x float> [[B:%.*]], <8 x i32> <i32 14, i32 13, i32 poison, i32 8, i32 6, i32 4, i32 2, i32 0>
+; AVX-NEXT:    [[TMP2:%.*]] = shufflevector <8 x float> [[A]], <8 x float> [[B]], <8 x i32> <i32 15, i32 12, i32 poison, i32 9, i32 7, i32 5, i32 3, i32 1>
 ; AVX-NEXT:    [[RESULT:%.*]] = fadd <8 x float> [[TMP1]], [[TMP2]]
 ; AVX-NEXT:    ret <8 x float> [[RESULT]]
 ;
diff --git a/llvm/test/Transforms/PhaseOrdering/X86/hsub.ll b/llvm/test/Transforms/PhaseOrdering/X86/hsub.ll
index fd160b7c57024..98d35f862d418 100644
--- a/llvm/test/Transforms/PhaseOrdering/X86/hsub.ll
+++ b/llvm/test/Transforms/PhaseOrdering/X86/hsub.ll
@@ -121,12 +121,12 @@ define <8 x i16> @sub_v8i16_u1234567(<8 x i16> %a, <8 x i16> %b) {
 
 define <8 x i16> @sub_v8i16_76u43210(<8 x i16> %a, <8 x i16> %b) {
 ; SSE2-LABEL: @sub_v8i16_76u43210(
-; SSE2-NEXT:    [[SHIFT:%.*]] = shufflevector <8 x i16> [[A:%.*]], <8 x i16> poison, <8 x i32> <i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE2-NEXT:    [[TMP1:%.*]] = sub <8 x i16> [[A]], [[SHIFT]]
 ; SSE2-NEXT:    [[SHIFT2:%.*]] = shufflevector <8 x i16> [[B:%.*]], <8 x i16> poison, <8 x i32> <i32 poison, i32 poison, i32 poison, i32 poison, i32 5, i32 poison, i32 poison, i32 poison>
 ; SSE2-NEXT:    [[TMP2:%.*]] = sub <8 x i16> [[B]], [[SHIFT2]]
 ; SSE2-NEXT:    [[SHIFT3:%.*]] = shufflevector <8 x i16> [[B]], <8 x i16> poison, <8 x i32> <i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 6>
 ; SSE2-NEXT:    [[TMP3:%.*]] = sub <8 x i16> [[SHIFT3]], [[B]]
+; SSE2-NEXT:    [[TMP7:%.*]] = shufflevector <8 x i16> [[A:%.*]], <8 x i16> poison, <8 x i32> <i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE2-NEXT:    [[TMP1:%.*]] = sub <8 x i16> [[A]], [[TMP7]]
 ; SSE2-NEXT:    [[TMP4:%.*]] = shufflevector <8 x i16> [[A]], <8 x i16> [[B]], <8 x i32> <i32 2, i32 4, i32 6, i32 8, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE2-NEXT:    [[TMP5:%.*]] = shufflevector <8 x i16> [[A]], <8 x i16> [[B]], <8 x i32> <i32 3, i32 5, i32 7, i32 9, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE2-NEXT:    [[TMP6:%.*]] = sub <8 x i16> [[TMP4]], [[TMP5]]
@@ -398,13 +398,13 @@ define <16 x i16> @sub_v16i16_FEuCBA98765432u0(<16 x i16> %a, <16 x i16> %b) {
 ; SSE4-LABEL: @sub_v16i16_FEuCBA98765432u0(
 ; SSE4-NEXT:    [[TMP2:%.*]] = shufflevector <16 x i16> [[A:%.*]], <16 x i16> [[B:%.*]], <16 x i32> <i32 1, i32 poison, i32 5, i32 7, i32 17, i32 19, i32 21, i32 23, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE4-NEXT:    [[TMP10:%.*]] = shufflevector <16 x i16> [[TMP2]], <16 x i16> [[A]], <16 x i32> <i32 0, i32 poison, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 25, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 0, i32 poison, i32 4, i32 6, i32 16, i32 18, i32 20, i32 22, i32 8, i32 poison, i32 10, i32 12, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <16 x i16> [[TMP10]], <16 x i16> [[A]], <16 x i32> <i32 0, i32 poison, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 poison, i32 27, i32 29, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 0, i32 poison, i32 4, i32 6, i32 16, i32 18, i32 20, i32 22, i32 8, i32 10, i32 12, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <16 x i16> [[TMP10]], <16 x i16> [[A]], <16 x i32> <i32 0, i32 poison, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 27, i32 29, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE4-NEXT:    [[TMP6:%.*]] = sub <16 x i16> [[TMP4]], [[TMP5]]
-; SSE4-NEXT:    [[TMP7:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 14, i32 24, i32 28, i32 30, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; SSE4-NEXT:    [[TMP8:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 15, i32 25, i32 29, i32 31, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP7:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 14, i32 24, i32 poison, i32 28, i32 30, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+; SSE4-NEXT:    [[TMP8:%.*]] = shufflevector <16 x i16> [[A]], <16 x i16> [[B]], <16 x i32> <i32 15, i32 25, i32 poison, i32 29, i32 31, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
 ; SSE4-NEXT:    [[TMP9:%.*]] = sub <16 x i16> [[TMP7]], [[TMP8]]
-; SSE4-NEXT:    [[RESULT:%.*]] = shufflevector <16 x i16> [[TMP9]], <16 x i16> [[TMP6]], <16 x i32> <i32 3, i32 2, i32 poison, i32 1, i32 0, i32 27, i32 26, i32 24, i32 23, i32 22, i32 21, i32 20, i32 19, i32 18, i32 poison, i32 16>
+; SSE4-NEXT:    [[RESULT:%.*]] = shufflevector <16 x i16> [[TMP9]], <16 x i16> [[TMP6]], <16 x i32> <i32 4, i32 3, i32 poison, i32 1, i32 0, i32 26, i32 25, i32 24, i32 23, i32 22, i32 21, i32 20, i32 19, i32 18, i32 poison, i32 16>
 ; SSE4-NEXT:    ret <16 x i16> [[RESULT]]
 ;
 ; AVX2-LABEL: @sub_v16i16_FEuCBA98765432u0(
@@ -1177,14 +1177,14 @@ define <8 x float> @sub_v8f32_76u43210(<8 x float> %a, <8 x float> %b) {
 ; SSE2-NEXT:    ret <8 x float> [[RESULT]]
 ;
 ; SSE4-LABEL: @sub_v8f32_76u43210(
-; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <8 x float> [[B:%.*]], <8 x float> [[A:%.*]], <8 x i32> <i32 6, i32 4, i32 poison, i32 0, i32 14, i32 12, i32 10, i32 8>
-; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <8 x float> [[B]], <8 x float> [[A]], <8 x i32> <i32 7, i32 5, i32 poison, i32 1, i32 15, i32 13, i32 11, i32 9>
+; SSE4-NEXT:    [[TMP4:%.*]] = shufflevector <8 x float> [[A:%.*]], <8 x float> [[B:%.*]], <8 x i32> <i32 14, i32 12, i32 poison, i32 8, i32 6, i32 4, i32 2, i32 0>
+; SSE4-NEXT:    [[TMP5:%.*]] = shufflevector <8 x float> [[A]], <8 x float> [[B]], <8 x i32> <i32 15, i32 13, i32 poison, i32 9, i32 7, i32 5, i32 3, i32 1>
 ; SSE4-NEXT:    [[TMP6:%.*]] = fsub <8 x float> [[TMP4]], [[TMP5]]
 ; SSE4-NEXT:    ret <8 x float> [[TMP6]]
 ;
 ; AVX-LABEL: @sub_v8f32_76u43210(
-; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <8 x float> [[B:%.*]], <8 x float> [[A:%.*]], <8 x i32> <i32 6, i32 4, i32 poison, i32 0, i32 14, i32 12, i32 10, i32 8>
-; AVX-NEXT:    [[TMP2:%.*]] = shufflevector <8 x float> [[B]], <8 x float> [[A]], <8 x i32> <i32 7, i32 5, i32 poison, i32 1, i32 15, i32 13, i32 11, i32 9>
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <8 x float> [[A:%.*]], <8 x float> [[B:%.*]], <8 x i32> <i32 14, i32 12, i32 poison, i32 8, i32 6, i32 4, i32 2, i32 0>
+; AVX-NEXT:    [[TMP2:%.*]] = shufflevector <8 x float> [[A]], <8 x float> [[B]], <8 x i32> <i32 15, i32 13, i32 poison, i32 9, i32 7, i32 5, i32 3, i32 1>
 ; AVX-NEXT:    [[RESULT:%.*]] = fsub <8 x float> [[TMP1]], [[TMP2]]
 ; AVX-NEXT:    ret <8 x float> [[RESULT]]
 ;
diff --git a/llvm/test/Transforms/VectorCombine/AArch64/ext-extract.ll b/llvm/test/Transforms/VectorCombine/AArch64/ext-extract.ll
index 60700412686ea..7358ebf637662 100644
--- a/llvm/test/Transforms/VectorCombine/AArch64/ext-extract.ll
+++ b/llvm/test/Transforms/VectorCombine/AArch64/ext-extract.ll
@@ -17,11 +17,21 @@ define void @zext_v4i8_all_lanes_used(<4 x i8> %src) {
 ; CHECK-NEXT:    [[TMP6:%.*]] = lshr i32 [[TMP1]], 8
 ; CHECK-NEXT:    [[TMP7:%.*]] = and i32 [[TMP6]], 255
 ; CHECK-NEXT:    [[TMP9:%.*]] = and i32 [[TMP1]], 255
-; CHECK-NEXT:    [[EXT9:%.*]] = zext nneg <4 x i8> [[SRC]] to <4 x i32>
-; CHECK-NEXT:    [[EXT_0:%.*]] = extractelement <4 x i32> [[EXT9]], i64 0
-; CHECK-NEXT:    [[EXT_1:%.*]] = extractelement <4 x i32> [[EXT9]], i64 1
-; CHECK-NEXT:    [[EXT_2:%.*]] = extractelement <4 x i32> [[EXT9]], i64 2
-; CHECK-NEXT:    [[EXT_3:%.*]] = extractelement <4 x i32> [[EXT9]], i64 3
+; CHECK-NEXT:    [[TMP8:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP23:%.*]] = bitcast <4 x i8> [[TMP8]] to i32
+; CHECK-NEXT:    [[TMP10:%.*]] = lshr i32 [[TMP23]], 24
+; CHECK-NEXT:    [[TMP11:%.*]] = lshr i32 [[TMP23]], 16
+; CHECK-NEXT:    [[TMP12:%.*]] = and i32 [[TMP11]], 255
+; CHECK-NEXT:    [[TMP13:%.*]] = lshr i32 [[TMP23]], 8
+; CHECK-NEXT:    [[TMP14:%.*]] = and i32 [[TMP13]], 255
+; CHECK-NEXT:    [[TMP15:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP16:%.*]] = bitcast <4 x i8> [[TMP15]] to i32
+; CHECK-NEXT:    [[TMP17:%.*]] = lshr i32 [[TMP16]], 24
+; CHECK-NEXT:    [[TMP18:%.*]] = lshr i32 [[TMP16]], 16
+; CHECK-NEXT:    [[TMP19:%.*]] = and i32 [[TMP18]], 255
+; CHECK-NEXT:    [[TMP20:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP21:%.*]] = bitcast <4 x i8> [[TMP20]] to i32
+; CHECK-NEXT:    [[TMP22:%.*]] = lshr i32 [[TMP21]], 24
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP9]])
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP7]])
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP5]])
@@ -83,10 +93,14 @@ define void @zext_v4i8_3_lanes_used_1(<4 x i8> %src) {
 ; CHECK-NEXT:    [[TMP5:%.*]] = and i32 [[TMP4]], 255
 ; CHECK-NEXT:    [[TMP6:%.*]] = lshr i32 [[TMP1]], 8
 ; CHECK-NEXT:    [[TMP7:%.*]] = and i32 [[TMP6]], 255
-; CHECK-NEXT:    [[EXT9:%.*]] = zext nneg <4 x i8> [[SRC]] to <4 x i32>
-; CHECK-NEXT:    [[EXT_1:%.*]] = extractelement <4 x i32> [[EXT9]], i64 1
-; CHECK-NEXT:    [[EXT_2:%.*]] = extractelement <4 x i32> [[EXT9]], i64 2
-; CHECK-NEXT:    [[EXT_3:%.*]] = extractelement <4 x i32> [[EXT9]], i64 3
+; CHECK-NEXT:    [[TMP15:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP8:%.*]] = bitcast <4 x i8> [[TMP15]] to i32
+; CHECK-NEXT:    [[TMP9:%.*]] = lshr i32 [[TMP8]], 24
+; CHECK-NEXT:    [[TMP10:%.*]] = lshr i32 [[TMP8]], 16
+; CHECK-NEXT:    [[TMP11:%.*]] = and i32 [[TMP10]], 255
+; CHECK-NEXT:    [[TMP12:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP13:%.*]] = bitcast <4 x i8> [[TMP12]] to i32
+; CHECK-NEXT:    [[TMP14:%.*]] = lshr i32 [[TMP13]], 24
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP7]])
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP5]])
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP2]])
@@ -114,10 +128,14 @@ define void @zext_v4i8_3_lanes_used_2(<4 x i8> %src) {
 ; CHECK-NEXT:    [[TMP4:%.*]] = lshr i32 [[TMP1]], 8
 ; CHECK-NEXT:    [[TMP5:%.*]] = and i32 [[TMP4]], 255
 ; CHECK-NEXT:    [[TMP7:%.*]] = and i32 [[TMP1]], 255
-; CHECK-NEXT:    [[EXT9:%.*]] = zext nneg <4 x i8> [[SRC]] to <4 x i32>
-; CHECK-NEXT:    [[EXT_0:%.*]] = extractelement <4 x i32> [[EXT9]], i64 0
-; CHECK-NEXT:    [[EXT_1:%.*]] = extractelement <4 x i32> [[EXT9]], i64 1
-; CHECK-NEXT:    [[EXT_3:%.*]] = extractelement <4 x i32> [[EXT9]], i64 3
+; CHECK-NEXT:    [[TMP6:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP14:%.*]] = bitcast <4 x i8> [[TMP6]] to i32
+; CHECK-NEXT:    [[TMP8:%.*]] = lshr i32 [[TMP14]], 24
+; CHECK-NEXT:    [[TMP9:%.*]] = lshr i32 [[TMP14]], 8
+; CHECK-NEXT:    [[TMP10:%.*]] = and i32 [[TMP9]], 255
+; CHECK-NEXT:    [[TMP11:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP12:%.*]] = bitcast <4 x i8> [[TMP11]] to i32
+; CHECK-NEXT:    [[TMP13:%.*]] = lshr i32 [[TMP12]], 24
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP7]])
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP5]])
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP2]])
@@ -145,9 +163,10 @@ define void @zext_v4i8_2_lanes_used_1(<4 x i8> %src) {
 ; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], 255
 ; CHECK-NEXT:    [[TMP4:%.*]] = lshr i32 [[TMP1]], 8
 ; CHECK-NEXT:    [[TMP5:%.*]] = and i32 [[TMP4]], 255
-; CHECK-NEXT:    [[EXT9:%.*]] = zext nneg <4 x i8> [[SRC]] to <4 x i32>
-; CHECK-NEXT:    [[EXT_1:%.*]] = extractelement <4 x i32> [[EXT9]], i64 1
-; CHECK-NEXT:    [[EXT_2:%.*]] = extractelement <4 x i32> [[EXT9]], i64 2
+; CHECK-NEXT:    [[TMP6:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP7:%.*]] = bitcast <4 x i8> [[TMP6]] to i32
+; CHECK-NEXT:    [[TMP8:%.*]] = lshr i32 [[TMP7]], 16
+; CHECK-NEXT:    [[TMP9:%.*]] = and i32 [[TMP8]], 255
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP5]])
 ; CHECK-NEXT:    call void @use.i32(i32 [[TMP3]])
 ; CHECK-NEXT:    ret void
@@ -171,9 +190,10 @@ define void @zext_v4i8_2_lanes_used_2(<4 x i8> %src) {
 ; CHECK-NEXT:    [[TMP2:%.*]] = lshr i32 [[TMP1]], 16
 ; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], 255
 ; CHECK-NEXT:    [[TMP5:%.*]] = and i32 [[TMP1]], 255
-; CHECK-NEXT:    [[EXT9:%.*]] = zext nneg <4 x i8> [[SRC]] to <4 x i32>
-; CHECK-NEXT:    [...
[truncated]

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⚠️ undef deprecator found issues in your code. ⚠️

You can test this locally with the following command: 
git diff -U0 --pickaxe-regex -S '([^a-zA-Z0-9#_-]undef[^a-zA-Z0-9_-]|UndefValue::get)' 'HEAD~1' HEAD llvm/lib/Transforms/Vectorize/VectorCombine.cpp llvm/test/Transforms/PhaseOrdering/X86/hadd.ll llvm/test/Transforms/PhaseOrdering/X86/hsub.ll llvm/test/Transforms/VectorCombine/AArch64/ext-extract.ll llvm/test/Transforms/VectorCombine/AArch64/load-extractelement-scalarization.ll llvm/test/Transforms/VectorCombine/AArch64/select-shuffle.ll llvm/test/Transforms/VectorCombine/RISCV/load-widening.ll llvm/test/Transforms/VectorCombine/X86/concat-boolmasks.ll llvm/test/Transforms/VectorCombine/X86/extract-binop-inseltpoison.ll llvm/test/Transforms/VectorCombine/X86/extract-binop.ll llvm/test/Transforms/VectorCombine/X86/reduction-two-vecs-combine.ll llvm/test/Transforms/VectorCombine/X86/select-shuffle.ll llvm/test/Transforms/VectorCombine/pr88796.ll

The following files introduce new uses of undef:

  • llvm/test/Transforms/VectorCombine/AArch64/select-shuffle.ll

Undef is now deprecated and should only be used in the rare cases where no replacement is possible. For example, a load of uninitialized memory yields undef. You should use poison values for placeholders instead.

In tests, avoid using undef and having tests that trigger undefined behavior. If you need an operand with some unimportant value, you can add a new argument to the function and use that instead.

For example, this is considered a bad practice:

define void @fn() {
  ...
  br i1 undef, ...
}

Please use the following instead:

define void @fn(i1 %cond) {
  ...
  br i1 %cond, ...
}

Please refer to the Undefined Behavior Manual for more information.

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⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command: 
git-clang-format --diff HEAD~1 HEAD --extensions cpp -- llvm/lib/Transforms/Vectorize/VectorCombine.cpp
View the diff from clang-format here. 
diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index 3c7101c9f..9d7d2d00e 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -3803,7 +3803,7 @@ bool VectorCombine::run() {
     }
   };
 
-  SmallVector<Instruction*, 128> InstrsForInstructionWorklist;
+  SmallVector<Instruction *, 128> InstrsForInstructionWorklist;
   for (BasicBlock &BB : F) {
     // Ignore unreachable basic blocks.
     if (!DT.isReachableFromEntry(&BB))

nikic
nikic reviewed Jul 16, 2025
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Compile-time: https://llvm-compile-time-tracker.com/compare.php?from=60579ec3059b2b6cc9dad90eaac1ed363fc395a7&to=7322d4b393c94af7164439419100d9c25df1e420&stat=instructions:u

Adding the entire function to the worklist at once is quite expensive...

Possibly we could do something more targeted at removing dead instructions early?

@davemgreen
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davemgreen commented Jul 17, 2025 •
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Compile-time: https://llvm-compile-time-tracker.com/compare.php?from=60579ec3059b2b6cc9dad90eaac1ed363fc395a7&to=7322d4b393c94af7164439419100d9c25df1e420&stat=instructions:u

Adding the entire function to the worklist at once is quite expensive...

Possibly we could do something more targeted at removing dead instructions early?

Thanks, Yeah it is probably not be very useful for a lot of node - many will not be vector instructions. I will look into erasing the instructions as we replace them if we can.

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@nikic nikic nikic left review comments

@fhahn fhahn Awaiting requested review from fhahn

@RKSimon RKSimon Awaiting requested review from RKSimon

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