[llvm] [LV] Fix unsafe canVectorizeWithIfConvert() checks (PR #203273)

[Gaëtan Bossu via llvm-commits]

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@@ -2962,7 +2962,10 @@ bool LoopAccessInfo::blockNeedsPredication(const BasicBlock *BB,
   assert(TheLoop->contains(BB) && "Unknown block used");
 
   // Blocks that do not dominate the latch need predication.
+  // Treat blocks in loops with no unique latch as always needing predication.
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gbossu wrote:

I meant for these two comments to go hand in hand, but I don't mind moving the first one down if you think that's clearer. :)

I'm also wondering whether I should add more context here because this in theory does not belong to LoopVectorizer.

https://github.com/llvm/llvm-project/pull/203273