[llvm] [Loads] Check loop-varying pointer in isDereferenceableAndAlignedInLoop. (PR #120962)

[Philip Reames via llvm-commits]

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@@ -290,6 +290,19 @@ bool llvm::isDereferenceableAndAlignedInLoop(
     return isDereferenceableAndAlignedPointer(Ptr, Alignment, EltSize, DL,
                                               HeaderFirstNonPHI, AC, &DT);
 
+  // If the load executes in a successor of the header, check if the
+  // loop-varying pointer is dereferenceable and aligned at the branch in the
+  // header. This is stricter than necessary and we could instead look for any
+  // block in the loop that executes unconditionally and post-dominates the
+  // block with the access.
+  if (LI->getParent() != L->getHeader() &&
+      L->getExitingBlock() == L->getLoopLatch() &&
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preames wrote:

What if the loop has multiple exiting blocks and multiple latches?  (i.e. nullptr == nullptr)

What if Ptr isn't defined in the header?

https://github.com/llvm/llvm-project/pull/120962