[llvm] [IndVars] Improve code; use SCEVPatternMatch (NFC) (PR #139533)

[Nikita Popov via llvm-commits]

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@@ -806,12 +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;
-
-  const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
-  if (!Step || !Step->isOne())
+  const SCEV *S = SE->getSCEV(Phi);
+  if (!match(S, m_scev_AffineAddRec(m_SCEV(), m_scev_One())) ||
+      cast<SCEVAddRecExpr>(S)->getLoop() != L)
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nikic wrote:

Might make sense to have a m_scev_AffineAddRec variant that takes the Loop as an argument?

https://github.com/llvm/llvm-project/pull/139533