[llvm] [SDAG] Teach FoldConstantArithmetic to match splats inserted into vectors (PR #163984)

[Benjamin Maxwell via llvm-commits]

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@@ -8,7 +8,7 @@
 define void @pr35443() {
 ; CHECK-LABEL: pr35443:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    vpbroadcastb ac+4(%rip), %xmm0
+; CHECK-NEXT:    vpbroadcastb ac+4(%rip), %ymm0
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MacDue wrote:

I've come up with #164624 as a fairly conservative IR level approach. 

https://github.com/llvm/llvm-project/pull/163984