[llvm] [InstCombine] Limit canonicalization of extractelement(cast) to constant index or same basic block. (PR #166227)

[Nikita Popov via llvm-commits]

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@@ -588,7 +588,8 @@ Instruction *InstCombinerImpl::visitExtractElementInst(ExtractElementInst &EI) {
       // Canonicalize extractelement(cast) -> cast(extractelement).
       // Bitcasts can change the number of vector elements, and they cost
       // nothing.
-      if (CI->hasOneUse() && (CI->getOpcode() != Instruction::BitCast)) {
+      if (CI->hasOneUse() && (CI->getOpcode() != Instruction::BitCast) &&
+          (EI.getParent() == CI->getParent() || isa<ConstantInt>(Index))) {
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nikic wrote:

Add a comment for why this limitation exists?

https://github.com/llvm/llvm-project/pull/166227