[llvm] [X86] Merge insertsubvector(load(p0),load_subv(p0),hi) -> subvbroadcast(p0) if either load is oneuse (PR #128857)

[Simon Pilgrim via llvm-commits]

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@@ -58562,8 +58562,9 @@ static SDValue combineINSERT_SUBVECTOR(SDNode *N, SelectionDAG &DAG,
 
   // If we're splatting the lower half subvector of a full vector load into the
   // upper half, attempt to create a subvector broadcast.
-  if (IdxVal == (OpVT.getVectorNumElements() / 2) && SubVec.hasOneUse() &&
-      Vec.getValueSizeInBits() == (2 * SubVec.getValueSizeInBits())) {
+  if (IdxVal == (OpVT.getVectorNumElements() / 2) &&
+      Vec.getValueSizeInBits() == (2 * SubVec.getValueSizeInBits()) &&
+      (Vec.hasOneUse() || SubVec.hasOneUse())) {
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RKSimon wrote:

The oneuse checks are still preventing some regressions due to shouldReduceLoadWidth being so permissive, but I've at least ensured that any other uses SubVec are replaced now.

https://github.com/llvm/llvm-project/pull/128857