[IndVars] Use m_scev_AffineAddRec

Author: artagnon

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -807,11 +807,9 @@ static bool isLoopCounter(PHINode* Phi, Loop *L,
   if (!SE->isSCEVable(Phi->getType()))
     return false;
 
-  const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi));
-  if (!AR || AR->getLoop() != L || !AR->isAffine())
-    return false;
-
-  if (!match(AR->getStepRecurrence(*SE), m_scev_SpecificInt(1)))
+  const SCEV *S = SE->getSCEV(Phi);
+  if (!match(S, m_scev_AffineAddRec(m_SCEV(), m_scev_One())) ||
+      cast<SCEVAddRecExpr>(S)->getLoop() != L)
     return false;
 
   int LatchIdx = Phi->getBasicBlockIndex(L->getLoopLatch());