[llvm] [SCEV] Fix infinite recursion in getZeroExtendExpr via missing Depth propagation (PR #184958)

[via llvm-commits]

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@@ -2719,11 +2719,11 @@ const SCEV *ScalarEvolution::getAddExpr(SmallVectorImpl<const SCEV *> &Ops,
     if (match(B, m_scev_ZExt(m_scev_Add(InnerAdd)))) {
       const SCEV *NarrowA = getTruncateExpr(A, InnerAdd->getType());
       if (NarrowA == getNegativeSCEV(InnerAdd->getOperand(0)) &&
-          getZeroExtendExpr(NarrowA, B->getType()) == A &&
+          getZeroExtendExpr(NarrowA, B->getType(), Depth) == A &&
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dean-mccoppin wrote:

Good point — `Depth + 1` is more consistent with every other recursive call site and I have no strong reason to prefer `Depth` here. The guard check at line 2722 is a speculative equality probe rather than a deeper recursive computation, which was my original (weak) justification, but `Depth + 1` is equally correct and avoids the inconsistency. I'll update both sites.

https://github.com/llvm/llvm-project/pull/184958