[clang] [Clang] Freeze padded vectors before storing. (PR #164821)

[Nikita Popov via cfe-commits]

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@@ -2300,6 +2300,9 @@ void CodeGenFunction::EmitStoreOfScalar(llvm::Value *Value, Address Addr,
         SmallVector<int, 16> Mask(NewVecTy->getNumElements(), -1);
         std::iota(Mask.begin(), Mask.begin() + VecTy->getNumElements(), 0);
         Value = Builder.CreateShuffleVector(Value, Mask, "extractVec");
+        // The extra lanes will be poison. Freeze the whole vector to make sure
+        // the padding memory is not poisoned, which may break coercion.
+        Value = Builder.CreateFreeze(Value);
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nikic wrote:

Instead of freezing, can we shuffle in undef instead? Or does that end up being worse?

https://github.com/llvm/llvm-project/pull/164821