[llvm] [SCEV] Try to fold ZExt/SExt of AddRec before existing lookup. (PR #208805)

[Ramkumar Ramachandra via llvm-commits]

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@@ -1701,6 +1701,18 @@ const SCEV *ScalarEvolution::getZeroExtendExprImpl(const SCEV *Op, Type *Ty,
   if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
     return getZeroExtendExpr(SZ->getOperand(), Ty, Depth + 1);
 
+  // If the operand is an affine AddRec with the no-unsigned-wrap flag, the
+  // zero-extension distributes over the recurrence.
+  if (Depth <= MaxCastDepth)
+    if (const auto *AR = dyn_cast<SCEVAddRecExpr>(Op))
+      if (AR->isAffine() && AR->hasNoUnsignedWrap()) {
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artagnon wrote:

Could write this as m_scev_AffineAddRec capturing an m_Loop?

https://github.com/llvm/llvm-project/pull/208805