[llvm] [VectorCombine] Add support for zext/sext/trunc to shuffleToIdentity (PR #92696)

[David Green via llvm-commits]

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@@ -754,10 +720,8 @@ define void @trunc(<8 x i64> %a, <8 x i64> %b, ptr %p) {
 
 define <4 x i64> @zext_chain(<4 x i16> %x) {
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davemgreen wrote:

Yeah It should be correct, if not optimal. The algorithm needs to check for extra uses to make sure that there will not introduce more instructions. This isn't true of the highest shuffle though, which does not have the same one-use check requirement.

https://github.com/llvm/llvm-project/pull/92696