[llvm] [VectorCombine] Add a cost model for shuffleToIdentity. (PR #93937)

[David Green via llvm-commits]

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@@ -1803,7 +1811,7 @@ bool VectorCombine::foldShuffleToIdentity(Instruction &I) {
           Value *V = IL.first;
           return !V || V == FrontV;
         })) {
-      SplatLeafs.insert(FrontV);
+      ConstLeafs.insert(FrontV);
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davemgreen wrote:

I don't think so, it seems fine, and it can be useful to keep the constant splats separate from the splats. The representation change eventually if we support more constants and do not want to keep them as splats.

https://github.com/llvm/llvm-project/pull/93937