[llvm] [VectorCombine][AMDGPU] Narrow Phi of Shuffles. (PR #140188)

[Simon Pilgrim via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=vector-combine -S -mtriple=amdgcn-amd-amdhsa | FileCheck %s --check-prefixes=CHECK
+
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RKSimon wrote:

many of these tests aren't currently folding  is it possible to use a range of arch targets with different costs to show the diffs?

https://github.com/llvm/llvm-project/pull/140188