[IVDesc] Use SCEVPatternMatch to improve code (NFC) #168397

artagnon · 2025-11-17T16:30:58Z

No description provided.

llvmbot · 2025-11-17T16:31:38Z

@llvm/pr-subscribers-llvm-analysis
@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-vectorizers

Author: Ramkumar Ramachandra (artagnon)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/168397.diff

4 Files Affected:

(modified) llvm/include/llvm/Analysis/IVDescriptors.h (+1-1)
(modified) llvm/lib/Analysis/IVDescriptors.cpp (+19-30)
(modified) llvm/lib/Analysis/LoopInfo.cpp (+1-1)
(modified) llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp (+2-2)

diff --git a/llvm/include/llvm/Analysis/IVDescriptors.h b/llvm/include/llvm/Analysis/IVDescriptors.h
index 654a5f10cea96..2b7707db9d16b 100644
--- a/llvm/include/llvm/Analysis/IVDescriptors.h
+++ b/llvm/include/llvm/Analysis/IVDescriptors.h
@@ -401,7 +401,7 @@ class InductionDescriptor {
   InductionKind getKind() const { return IK; }
   const SCEV *getStep() const { return Step; }
   BinaryOperator *getInductionBinOp() const { return InductionBinOp; }
-  LLVM_ABI ConstantInt *getConstIntStepValue() const;
+  LLVM_ABI const APInt *getStepValue() const;
 
   /// Returns true if \p Phi is an induction in the loop \p L. If \p Phi is an
   /// induction, the induction descriptor \p D will contain the data describing
diff --git a/llvm/lib/Analysis/IVDescriptors.cpp b/llvm/lib/Analysis/IVDescriptors.cpp
index 641850b46bbd8..409a45d6fc542 100644
--- a/llvm/lib/Analysis/IVDescriptors.cpp
+++ b/llvm/lib/Analysis/IVDescriptors.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ScalarEvolutionPatternMatch.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Instructions.h"
@@ -25,6 +26,7 @@
 
 using namespace llvm;
 using namespace llvm::PatternMatch;
+using namespace llvm::SCEVPatternMatch;
 
 #define DEBUG_TYPE "iv-descriptors"
 
@@ -719,11 +721,12 @@ RecurrenceDescriptor::isFindIVPattern(RecurKind Kind, Loop *TheLoop,
     if (!SE.isSCEVable(Ty))
       return std::nullopt;
 
-    auto *AR = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(V));
-    if (!AR || AR->getLoop() != TheLoop)
+    auto *AR = SE.getSCEV(V);
+    const SCEV *Step;
+    if (!match(AR, m_scev_AffineAddRec(m_SCEV(), m_SCEV(Step),
+                                       m_SpecificLoop(TheLoop))))
       return std::nullopt;
 
-    const SCEV *Step = AR->getStepRecurrence(SE);
     if ((isFindFirstIVRecurrenceKind(Kind) && !SE.isKnownNegative(Step)) ||
         (isFindLastIVRecurrenceKind(Kind) && !SE.isKnownPositive(Step)))
       return std::nullopt;
@@ -1377,7 +1380,7 @@ InductionDescriptor::InductionDescriptor(Value *Start, InductionKind K,
          "StartValue is not an integer for integer induction");
 
   // Check the Step Value. It should be non-zero integer value.
-  assert((!getConstIntStepValue() || !getConstIntStepValue()->isZero()) &&
+  assert((!getStepValue() || !getStepValue()->isZero()) &&
          "Step value is zero");
 
   assert((IK == IK_FpInduction || Step->getType()->isIntegerTy()) &&
@@ -1395,10 +1398,11 @@ InductionDescriptor::InductionDescriptor(Value *Start, InductionKind K,
     llvm::append_range(RedundantCasts, *Casts);
 }
 
-ConstantInt *InductionDescriptor::getConstIntStepValue() const {
-  if (isa<SCEVConstant>(Step))
-    return dyn_cast<ConstantInt>(cast<SCEVConstant>(Step)->getValue());
-  return nullptr;
+const APInt *InductionDescriptor::getStepValue() const {
+  const APInt *StepC;
+  if (!match(Step, m_scev_APInt(StepC)))
+    return nullptr;
+  return StepC;
 }
 
 bool InductionDescriptor::isFPInductionPHI(PHINode *Phi, const Loop *TheLoop,
@@ -1614,41 +1618,26 @@ bool InductionDescriptor::isInductionPHI(
 
   // Check that the PHI is consecutive.
   const SCEV *PhiScev = Expr ? Expr : SE->getSCEV(Phi);
-  const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PhiScev);
-
-  if (!AR) {
+  const SCEV *Step;
+  if (!match(PhiScev, m_scev_AffineAddRec(m_SCEV(), m_SCEV(Step),
+                                          m_SpecificLoop(TheLoop)))) {
     LLVM_DEBUG(dbgs() << "LV: PHI is not a poly recurrence.\n");
     return false;
   }
 
-  if (AR->getLoop() != TheLoop) {
-    // FIXME: We should treat this as a uniform. Unfortunately, we
-    // don't currently know how to handled uniform PHIs.
-    LLVM_DEBUG(
-        dbgs() << "LV: PHI is a recurrence with respect to an outer loop.\n");
-    return false;
-  }
-
   // This function assumes that InductionPhi is called only on Phi nodes
   // present inside loop headers. Check for the same, and throw an assert if
   // the current Phi is not present inside the loop header.
-  assert(Phi->getParent() == AR->getLoop()->getHeader()
-    && "Invalid Phi node, not present in loop header");
+  assert(Phi->getParent() == TheLoop->getHeader() &&
+         "Invalid Phi node, not present in loop header");
 
   Value *StartValue =
-      Phi->getIncomingValueForBlock(AR->getLoop()->getLoopPreheader());
+      Phi->getIncomingValueForBlock(TheLoop->getLoopPreheader());
 
-  BasicBlock *Latch = AR->getLoop()->getLoopLatch();
+  BasicBlock *Latch = TheLoop->getLoopLatch();
   if (!Latch)
     return false;
 
-  const SCEV *Step = AR->getStepRecurrence(*SE);
-  // Calculate the pointer stride and check if it is consecutive.
-  // The stride may be a constant or a loop invariant integer value.
-  const SCEVConstant *ConstStep = dyn_cast<SCEVConstant>(Step);
-  if (!ConstStep && !SE->isLoopInvariant(Step, TheLoop))
-    return false;
-
   if (PhiTy->isIntegerTy()) {
     BinaryOperator *BOp =
         dyn_cast<BinaryOperator>(Phi->getIncomingValueForBlock(Latch));
diff --git a/llvm/lib/Analysis/LoopInfo.cpp b/llvm/lib/Analysis/LoopInfo.cpp
index d84721b7f8f4b..7f261f21e1e5b 100644
--- a/llvm/lib/Analysis/LoopInfo.cpp
+++ b/llvm/lib/Analysis/LoopInfo.cpp
@@ -421,7 +421,7 @@ bool Loop::isCanonical(ScalarEvolution &SE) const {
   if (IndDesc.getInductionOpcode() != Instruction::Add)
     return false;
 
-  ConstantInt *Step = IndDesc.getConstIntStepValue();
+  const APInt *Step = IndDesc.getStepValue();
   if (!Step || !Step->isOne())
     return false;
 
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 03112c67dda7b..bc57ef5e71725 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -706,7 +706,7 @@ void LoopVectorizationLegality::addInductionPhi(
 
   // Int inductions are special because we only allow one IV.
   if (ID.getKind() == InductionDescriptor::IK_IntInduction &&
-      ID.getConstIntStepValue() && ID.getConstIntStepValue()->isOne() &&
+      ID.getStepValue() && ID.getStepValue()->isOne() &&
       isa<Constant>(ID.getStartValue()) &&
       cast<Constant>(ID.getStartValue())->isNullValue()) {
 
@@ -891,7 +891,7 @@ bool LoopVectorizationLegality::canVectorizeInstr(Instruction &I) {
           if (AllowStridedPointerIVs)
             return false;
           return ID.getKind() == InductionDescriptor::IK_PtrInduction &&
-                 ID.getConstIntStepValue() == nullptr;
+                 ID.getStepValue() == nullptr;
         };
 
     // TODO: Instead of recording the AllowedExit, it would be good to

llvm/lib/Analysis/IVDescriptors.cpp

Mel-Chen · 2025-11-18T08:29:48Z

llvm/lib/Analysis/IVDescriptors.cpp

-  // Calculate the pointer stride and check if it is consecutive.
-  // The stride may be a constant or a loop invariant integer value.
-  const SCEVConstant *ConstStep = dyn_cast<SCEVConstant>(Step);
-  if (!ConstStep && !SE->isLoopInvariant(Step, TheLoop))
-    return false;


Could we drop this? Do m_SCEV(Step) guarantee this?

Doesn't m_scev_AffineAddRec guarantee this?

I don't think m_scev_AffineAddRec guarantee this. It should depend on m_SCEV(Step).
If we use m_SCEVConstant(Step), Step is SCEVConstant. But, we use m_SCEV(Step), so it should only get a SCEV, and not guarantee anything, right?

From ScalarEvolutionExpressions:

/// Return true if this represents an expression A + B*x where A /// and B are loop invariant values. bool isAffine() const {

They must be loop-invariant if the AddRec is affine.

Hmm, this makes me wonder if const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PhiScev); is equivalent to match(PhiScev, m_scev_AffineAddRec()). Could PhiScev originally have been a quadratic?

It could have, but we'd have bailed out anyway when checking that the step is loop invariant? We're just bailing out ahead of time now, and this should be NFC?

llvm/include/llvm/Analysis/IVDescriptors.h

llvm/lib/Analysis/IVDescriptors.cpp

github-actions · 2025-11-18T11:03:36Z

🐧 Linux x64 Test Results

186270 tests passed
4853 tests skipped

artagnon · 2025-11-18T14:41:08Z

llvm/lib/Analysis/IVDescriptors.cpp

-    auto *AR = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(V));
-    if (!AR || AR->getLoop() != TheLoop)
+    auto *AR = SE.getSCEV(V);
+    const SCEV *Step;
+    if (!match(AR, m_scev_AffineAddRec(m_SCEV(), m_SCEV(Step),
+                                       m_SpecificLoop(TheLoop))))
      return std::nullopt;

-    const SCEV *Step = AR->getStepRecurrence(SE);


This code isn't directly equivalent, as we're restricting to affine AddRecs, when we weren't previously. However, I think Find(First|Last)IV wouldn't work with a non-affine AddRec anyway.

[IVDesc] Use SCEVPatternMatch to improve code (NFC)

b304148

artagnon requested review from Mel-Chen and fhahn November 17, 2025 16:30

llvmbot added vectorizers llvm:analysis Includes value tracking, cost tables and constant folding llvm:transforms labels Nov 17, 2025

Mel-Chen reviewed Nov 18, 2025

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fhahn reviewed Nov 18, 2025

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