[llvm] [VectorCombine] Preserve scoped alias metadata (PR #153714)

[Nikita Popov via llvm-commits]

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@@ -1831,6 +1835,14 @@ bool VectorCombine::scalarizeLoadExtract(Instruction &I) {
         LI->getAlign(), VecTy->getElementType(), Idx, *DL);
     NewLoad->setAlignment(ScalarOpAlignment);
 
+    if (MDNode *aliasScope = LI->getMetadata(aliasScopeKind)) {
+      NewLoad->setMetadata(aliasScopeKind, aliasScope);
+    }
+
+    if (MDNode *noAlias = LI->getMetadata(noAliasKind)) {
+      NewLoad->setMetadata(noAliasKind, noAlias);
+    }
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nikic wrote:

The type is `VecTy->getElementType()`. The offset would be Idx * the type size like here: https://github.com/llvm/llvm-project/blob/adce7479712bc329a2453efc5fcdf999587b646f/llvm/lib/Transforms/Vectorize/VectorCombine.cpp#L1652-L1654

The problem is if Idx is a variable. In that case the offset is unknown. So I would make the whole logic conditional on the `dyn_cast<ConstantInt>(Idx)` case.

https://github.com/llvm/llvm-project/pull/153714