[IVSimplify] Improve code in isLoopCounter (NFC)

Author: artagnon

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -38,6 +38,7 @@
 #include "llvm/Analysis/MemorySSAUpdater.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ScalarEvolutionPatternMatch.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
@@ -53,7 +54,6 @@
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
-#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/PatternMatch.h"
@@ -79,6 +79,7 @@
 
 using namespace llvm;
 using namespace PatternMatch;
+using namespace SCEVPatternMatch;
 
 #define DEBUG_TYPE "indvars"
 
@@ -810,8 +811,7 @@ static bool isLoopCounter(PHINode* Phi, Loop *L,
   if (!AR || AR->getLoop() != L || !AR->isAffine())
     return false;
 
-  const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
-  if (!Step || !Step->isOne())
+  if (!match(AR->getStepRecurrence(*SE), m_scev_SpecificInt(1)))
     return false;
 
   int LatchIdx = Phi->getBasicBlockIndex(L->getLoopLatch());