[PATCH] D151640: [LSV] Attempt to fix comparison of APInt's with different bit widths.

[Justin Lebar via Phabricator via llvm-commits]

jlebar created this revision.
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I have not been able to make a testcase for this, but this should be safe, and
it may fix the assertion being hit in https://reviews.llvm.org/D151630#4378572.

(We should absolutely figure out a testcase for this, either before or after
this is checked in.)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D151640

Files:
  llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp


Index: llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
@@ -1295,7 +1295,13 @@
       std::optional<APInt> FalseDiff =
           getConstantOffset(SelectA->getFalseValue(), SelectB->getFalseValue(),
                             ContextInst, Depth);
-      if (TrueDiff == FalseDiff)
+      // A bit unclear how we can get TrueDiff and FalseDiff with different bit
+      // widths, since the bit width returned by getConstantOffset is determined
+      // by the datatype of the pointer, and both sides of the `select` should
+      // have the same datatype.  But we seem to be hitting this in practice.
+      if (FalseDiff.has_value() &&
+          TrueDiff->getBitWidth() == FalseDiff->getBitWidth() &&
+          TrueDiff == FalseDiff)
         return TrueDiff;
     }
   }


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