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[InstCombine] Cleanup the TFE/LWE check in AMDGPU SimplifyDemanded

Authored by nhaehnle on Feb 4 2019, 1:24 PM.

Description

[InstCombine] Cleanup the TFE/LWE check in AMDGPU SimplifyDemanded

Summary:
The fix added in r352904 is not quite correct, or rather misleading:

  1. When the texfailctrl (TFC) argument was non-constant, the fix assumed non-TFE/LWE, which is incorrect.
  1. Regardless, this code path cannot even be hit for correct TFE/LWE-enabled calls, because those return a struct. Added a test case for those for completeness.

Change-Id: I92d314dbc67a2670f6d7adaab765ef45f56a49cf

Reviewers: hliao, dstuttard, arsenm

Subscribers: kzhuravl, jvesely, wdng, yaxunl, tpr, t-tye, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57681

llvm-svn: 353097