[llvm] [DAGCombiner] Require same type of splat & element for build_vector (PR #88284)

[Phoebe Wang via llvm-commits]

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@@ -23429,17 +23429,21 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
   // TODO: Maybe this is useful for non-splat too?
   if (!LegalOperations) {
     if (SDValue Splat = cast<BuildVectorSDNode>(N)->getSplatValue()) {
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phoebewang wrote:

The old code seems problematic, if we use `cast`, we don't need to use `if`.

https://github.com/llvm/llvm-project/pull/88284