[llvm] [GISel][AMDGPU] Expand ShuffleVector (PR #124527)

[Matt Arsenault via llvm-commits]

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@@ -1560,6 +1560,13 @@ def combine_shuffle_concat : GICombineRule<
         [{ return Helper.matchCombineShuffleConcat(*${root}, ${matchinfo}); }]),
   (apply [{ Helper.applyCombineShuffleConcat(*${root}, ${matchinfo}); }])>;
 
+// Combines shuffles of vector into extract_subvector
+def combine_shuffle_vector : GICombineRule<
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arsenm wrote:

Name is too broad, and doesn't match the comment. It says it forms an extract_subvector, but this is creating a build_vector 

https://github.com/llvm/llvm-project/pull/124527