[llvm] [AMDGPU][DAG] Allow extract_subvector for free register copy (PR #214152)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,139 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -mtriple=amdgcn -mcpu=gfx900 < %s -stop-after=amdgpu-isel | FileCheck %s
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arsenm wrote:

```suggestion
; RUN: llc -mtriple=amdgpu9.00-amd-amdhsa < %s -stop-after=amdgpu-isel | FileCheck %s
```

Don't use -stop-after?

https://github.com/llvm/llvm-project/pull/214152