[llvm] [InstCombine] Pull shuffles out of binops with splatted ops (PR #137948)

[Luke Lau via llvm-commits]

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@@ -2271,6 +2271,27 @@ Instruction *InstCombinerImpl::foldVectorBinop(BinaryOperator &Inst) {
     }
   }
 
+  // Similar to the combine above, but handles the case for scalable vectors
+  // where both V1 and C are splats.
+  //
+  // Op(shuffle(V1, 0), (splat C)) -> shuffle(Op(V1, (splat C)), 0)
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lukel97 wrote:

There's a check for `isSafeToSpeculativelyExecuteWithVariableReplaced` earlier on in the function which the previous combine also relies on, so I think this should also be covered in the new combine. I've added a negative test in e9d51e74cfeb274d263d85148e74b31937ca49dd

https://github.com/llvm/llvm-project/pull/137948