[PATCH] D22423: AMDGPU: Fix verifier error from partially undef copy

[Matt Arsenault via llvm-commits]

arsenm created this revision.
arsenm added a reviewer: MatzeB.
arsenm added a subscriber: llvm-commits.
Herald added a reviewer: tstellarAMD.
Herald added subscribers: kzhuravl, arsenm, MatzeB.

In this situation:
    

```
    %VGPR2<def> = BUFFER_LOAD_DWORD_OFFSET %SGPR8_SGPR9_SGPR10_SGPR11,
    %VGPR7<def,tied3> = V_MAC_F32_e32 %VGPR0<undef>, %VGPR1<kill>, %VGPR7<kill,tied0>, %EXEC<imp-use>
    %VGPR3_VGPR4_VGPR5_VGPR6<def> = COPY %VGPR0_VGPR1_VGPR2_VGPR3
    %VGPR4<def> = COPY %VGPR2
```
    
The copy for VGPR1 -> VGPR4 was an error from reading undefined VGPR1,
but VGPR4 is defined immediately after this copy.


https://reviews.llvm.org/D22423

Files:
  lib/Target/AMDGPU/SIInstrInfo.cpp
  test/CodeGen/AMDGPU/undefined-subreg-liverange.ll

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