[llvm] [LoongArch] Fix broadcast load with extension. (PR #155960)

[via llvm-commits]

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@@ -2471,8 +2471,10 @@ static SDValue lowerBUILD_VECTORAsBroadCastLoad(BuildVectorSDNode *BVOp,
   if (!IdentitySrc || !BVOp->isOnlyUserOf(IdentitySrc.getNode()))
     return SDValue();
 
-  if (IsIdeneity) {
-    auto *LN = cast<LoadSDNode>(IdentitySrc);
+  auto *LN = cast<LoadSDNode>(IdentitySrc);
+  auto ExtType = LN->getExtensionType();
+
+  if (IsIdeneity && (ExtType == ISD::EXTLOAD || ExtType == ISD::NON_EXTLOAD)) {
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heiher wrote:

I'm a bit concerned about assuming that `ISD::EXTLOAD` always implies `MemoryVT` and `VectorElementVT` are the same size. I can’t come up with a concrete counterexample right now, but I’m not entirely confident this will always hold true going forward. My preference would be to explicitly check that the two types have equal size, this way we can be sure the load width matches the vector element width, and it lines up cleanly with `vldrepl`.

https://github.com/llvm/llvm-project/pull/155960