[llvm] [LAA][NFC] Refactor deref no-wrap check; expose broken reverse-loop bounds (PR #211960)

[Antonio Frighetto via llvm-commits]

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@@ -268,54 +276,60 @@ static bool evaluatePtrAddRecAtMaxBTCWillNotWrap(
   MaxBTC = SE.getNoopOrZeroExtend(MaxBTC, WiderTy);
 
   // For the computations below, make sure they don't unsigned wrap.
-  if (!SE.isKnownPredicate(CmpInst::ICMP_UGE, AR->getStart(), StartPtr))
+  // FIXME: for a negative step this holds the HIGHEST accessed address, not
+  // the lowest
+  const SCEV *LowestAddr = AR->getStart();
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antoniofrighetto wrote:

It would still be incorrect for the negative-step path, though? I also think it would be cleaner to keep StartOffset here (and possibly introduce the new name in the fix PR).

https://github.com/llvm/llvm-project/pull/211960