[llvm] [SelectionDAG] Use unaligned store/load to move AVX registers onto stack for `insertelement` (PR #82130)

[Matt Arsenault via llvm-commits]

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@@ -1496,11 +1500,12 @@ SDValue SelectionDAGLegalize::ExpandInsertToVectorThroughStack(SDValue Op) {
     Ch = DAG.getTruncStore(
         Ch, dl, Part, SubStackPtr,
         MachinePointerInfo::getUnknownStack(DAG.getMachineFunction()),
-        VecVT.getVectorElementType());
+        VecVT.getVectorElementType(), ElementAlignment);
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arsenm wrote:

I'm still confused about what is going on with the alignment. Can you assert the resulting StoreSDNode's getAlign is the element alignment (the actual element alignment, not the misnamed ElementAlignment here)?

https://github.com/llvm/llvm-project/pull/82130