[llvm] [HashRecognize] Fix compiler crash on missing latch compare instruction (PR #211895)

[Sean Clarke via llvm-commits]

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@@ -512,7 +512,8 @@ std::variant<PolynomialInfo, StringRef> HashRecognize::recognizeCRC() const {
   BasicBlock *Latch = L.getLoopLatch();
   BasicBlock *Exit = L.getExitBlock();
   const PHINode *IndVar = L.getCanonicalInductionVariable();
-  if (!Latch || !Exit || !IndVar || L.getNumBlocks() != 1)
+  if (!Latch || !Exit || !IndVar || L.getNumBlocks() != 1 ||
+      !L.getLatchCmpInst())
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xarkenz wrote:

I'm not convinced it does:
```cpp
/// Return true if the loop induction variable starts at zero and increments
/// by one each time through the loop.
bool isCanonical(ScalarEvolution &SE) const;
```
It might be better to just keep the individual checks for clarity, unless there's some function that clearly covers all of these.

https://github.com/llvm/llvm-project/pull/211895