[llvm] [DAG] Teach SelectionDAGBuilder to read parameter alignment of compressstore/expandload. (PR #83763)

[Craig Topper via llvm-commits]

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@@ -4746,6 +4748,8 @@ void SelectionDAGBuilder::visitMaskedLoad(const CallInst &I, bool IsExpanding) {
     // @llvm.masked.expandload.*(Ptr, Mask, Src0)
     Ptr = I.getArgOperand(0);
     Alignment = std::nullopt;
+    if (MaybeAlign Align = I.getParamAlign(0))
+      Alignment = Align;
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topperc wrote:

I think we should be using `I.getParamAlign(0).getValueOr(DAG.getEVTAlign(1))`. The call to `DAG.getEVTAlign(VT)` later doesn't make sense for a compressed store or expanding load. The vector type isn't really relevant. Maybe we would use the alignment for the element type, but 1 is conservatively correct.

https://github.com/llvm/llvm-project/pull/83763