[llvm] [VPlan] Split out VPBlendRecipe simplifications from simplifyRecipes. NFC (PR #134073)
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Wed Apr 2 05:21:33 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-vectorizers
Author: Luke Lau (lukel97)
<details>
<summary>Changes</summary>
This is split off from #<!-- -->133977
VPBlendRecipe normalisation is sensitive to the number of users a mask has, so should probably be run after the masks are simplified as much as possible.
Note this could be run after removeDeadRecipes but this causes test diffs, some regressions, so this is left to a later patch.
---
Full diff: https://github.com/llvm/llvm-project/pull/134073.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp (+80-68)
- (modified) llvm/lib/Transforms/Vectorize/VPlanTransforms.h (+4)
``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 0c37db7f9d3a3..137ed330c31b2 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -926,74 +926,6 @@ static void recursivelyDeleteDeadRecipes(VPValue *V) {
static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
using namespace llvm::VPlanPatternMatch;
- if (auto *Blend = dyn_cast<VPBlendRecipe>(&R)) {
- // Try to remove redundant blend recipes.
- SmallPtrSet<VPValue *, 4> UniqueValues;
- if (Blend->isNormalized() || !match(Blend->getMask(0), m_False()))
- UniqueValues.insert(Blend->getIncomingValue(0));
- for (unsigned I = 1; I != Blend->getNumIncomingValues(); ++I)
- if (!match(Blend->getMask(I), m_False()))
- UniqueValues.insert(Blend->getIncomingValue(I));
-
- if (UniqueValues.size() == 1) {
- Blend->replaceAllUsesWith(*UniqueValues.begin());
- Blend->eraseFromParent();
- return;
- }
-
- if (Blend->isNormalized())
- return;
-
- // Normalize the blend so its first incoming value is used as the initial
- // value with the others blended into it.
-
- unsigned StartIndex = 0;
- for (unsigned I = 0; I != Blend->getNumIncomingValues(); ++I) {
- // If a value's mask is used only by the blend then is can be deadcoded.
- // TODO: Find the most expensive mask that can be deadcoded, or a mask
- // that's used by multiple blends where it can be removed from them all.
- VPValue *Mask = Blend->getMask(I);
- if (Mask->getNumUsers() == 1 && !match(Mask, m_False())) {
- StartIndex = I;
- break;
- }
- }
-
- SmallVector<VPValue *, 4> OperandsWithMask;
- OperandsWithMask.push_back(Blend->getIncomingValue(StartIndex));
-
- for (unsigned I = 0; I != Blend->getNumIncomingValues(); ++I) {
- if (I == StartIndex)
- continue;
- OperandsWithMask.push_back(Blend->getIncomingValue(I));
- OperandsWithMask.push_back(Blend->getMask(I));
- }
-
- auto *NewBlend = new VPBlendRecipe(
- cast<PHINode>(Blend->getUnderlyingValue()), OperandsWithMask);
- NewBlend->insertBefore(&R);
-
- VPValue *DeadMask = Blend->getMask(StartIndex);
- Blend->replaceAllUsesWith(NewBlend);
- Blend->eraseFromParent();
- recursivelyDeleteDeadRecipes(DeadMask);
-
- /// Simplify BLEND %a, %b, Not(%mask) -> BLEND %b, %a, %mask.
- VPValue *NewMask;
- if (NewBlend->getNumOperands() == 3 &&
- match(NewBlend->getMask(1), m_Not(m_VPValue(NewMask)))) {
- VPValue *Inc0 = NewBlend->getOperand(0);
- VPValue *Inc1 = NewBlend->getOperand(1);
- VPValue *OldMask = NewBlend->getOperand(2);
- NewBlend->setOperand(0, Inc1);
- NewBlend->setOperand(1, Inc0);
- NewBlend->setOperand(2, NewMask);
- if (OldMask->getNumUsers() == 0)
- cast<VPInstruction>(OldMask)->eraseFromParent();
- }
- return;
- }
-
// VPScalarIVSteps can only be simplified after unrolling. VPScalarIVSteps for
// part 0 can be replaced by their start value, if only the first lane is
// demanded.
@@ -1092,6 +1024,85 @@ void VPlanTransforms::simplifyRecipes(VPlan &Plan, Type &CanonicalIVTy) {
}
}
+void VPlanTransforms::simplifyBlends(VPlan &Plan) {
+ using namespace llvm::VPlanPatternMatch;
+ ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<VPBlockBase *>> RPOT(
+ Plan.getEntry());
+ SetVector<VPRecipeBase *> Worklist;
+ for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT)) {
+ for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
+ auto *Blend = dyn_cast<VPBlendRecipe>(&R);
+ if (!Blend)
+ continue;
+
+ // Try to remove redundant blend recipes.
+ SmallPtrSet<VPValue *, 4> UniqueValues;
+ if (Blend->isNormalized() || !match(Blend->getMask(0), m_False()))
+ UniqueValues.insert(Blend->getIncomingValue(0));
+ for (unsigned I = 1; I != Blend->getNumIncomingValues(); ++I)
+ if (!match(Blend->getMask(I), m_False()))
+ UniqueValues.insert(Blend->getIncomingValue(I));
+
+ if (UniqueValues.size() == 1) {
+ Blend->replaceAllUsesWith(*UniqueValues.begin());
+ Blend->eraseFromParent();
+ continue;
+ }
+
+ if (Blend->isNormalized())
+ continue;
+
+ // Normalize the blend so its first incoming value is used as the initial
+ // value with the others blended into it.
+
+ unsigned StartIndex = 0;
+ for (unsigned I = 0; I != Blend->getNumIncomingValues(); ++I) {
+ // If a value's mask is used only by the blend then is can be deadcoded.
+ // TODO: Find the most expensive mask that can be deadcoded, or a mask
+ // that's used by multiple blends where it can be removed from them all.
+ VPValue *Mask = Blend->getMask(I);
+ if (Mask->getNumUsers() == 1 && !match(Mask, m_False())) {
+ StartIndex = I;
+ break;
+ }
+ }
+
+ SmallVector<VPValue *, 4> OperandsWithMask;
+ OperandsWithMask.push_back(Blend->getIncomingValue(StartIndex));
+
+ for (unsigned I = 0; I != Blend->getNumIncomingValues(); ++I) {
+ if (I == StartIndex)
+ continue;
+ OperandsWithMask.push_back(Blend->getIncomingValue(I));
+ OperandsWithMask.push_back(Blend->getMask(I));
+ }
+
+ auto *NewBlend = new VPBlendRecipe(
+ cast<PHINode>(Blend->getUnderlyingValue()), OperandsWithMask);
+ NewBlend->insertBefore(&R);
+
+ VPValue *DeadMask = Blend->getMask(StartIndex);
+ Blend->replaceAllUsesWith(NewBlend);
+ Blend->eraseFromParent();
+ recursivelyDeleteDeadRecipes(DeadMask);
+
+ /// Simplify BLEND %a, %b, Not(%mask) -> BLEND %b, %a, %mask.
+ VPValue *NewMask;
+ if (NewBlend->getNumOperands() == 3 &&
+ match(NewBlend->getMask(1), m_Not(m_VPValue(NewMask)))) {
+ VPValue *Inc0 = NewBlend->getOperand(0);
+ VPValue *Inc1 = NewBlend->getOperand(1);
+ VPValue *OldMask = NewBlend->getOperand(2);
+ NewBlend->setOperand(0, Inc1);
+ NewBlend->setOperand(1, Inc0);
+ NewBlend->setOperand(2, NewMask);
+ if (OldMask->getNumUsers() == 0)
+ cast<VPInstruction>(OldMask)->eraseFromParent();
+ }
+ }
+ }
+}
+
/// Optimize the width of vector induction variables in \p Plan based on a known
/// constant Trip Count, \p BestVF and \p BestUF.
static bool optimizeVectorInductionWidthForTCAndVFUF(VPlan &Plan,
@@ -1687,6 +1698,7 @@ void VPlanTransforms::optimize(VPlan &Plan) {
runPass(removeRedundantInductionCasts, Plan);
runPass(simplifyRecipes, Plan, *Plan.getCanonicalIV()->getScalarType());
+ runPass(simplifyBlends, Plan);
runPass(removeDeadRecipes, Plan);
runPass(legalizeAndOptimizeInductions, Plan);
runPass(removeRedundantExpandSCEVRecipes, Plan);
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
index c23ff38265670..b008459ebad3f 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
@@ -183,6 +183,10 @@ struct VPlanTransforms {
/// CanonicalIVTy as type for all un-typed live-ins in VPTypeAnalysis.
static void simplifyRecipes(VPlan &Plan, Type &CanonicalIVTy);
+ /// Normalize and simplify VPBlendRecipes. Should be run after simplifyRecipes
+ /// to make sure the masks are simplified.
+ static void simplifyBlends(VPlan &Plan);
+
/// If there's a single exit block, optimize its phi recipes that use exiting
/// IV values by feeding them precomputed end values instead, possibly taken
/// one step backwards.
``````````
</details>
https://github.com/llvm/llvm-project/pull/134073
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