[llvm] [GlobalISel] Combine G_MERGE_VALUES of x and undef (PR #113616)

[Thorsten Schütt via llvm-commits]

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@@ -922,6 +922,9 @@ class CombinerHelper {
   bool matchUnmergeValuesAnyExtBuildVector(const MachineInstr &MI,
                                            BuildFnTy &MatchInfo);
 
+  // merge_values(_, undef) -> zext
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tschuett wrote:

I first want to rebase on https://github.com/llvm/llvm-project/pull/113764, then I can clean it up.

https://github.com/llvm/llvm-project/pull/113616