AMDGPU: Move v_readlane lane select from VGPR to SGPR
Summary:
Fix a compiler bug when the lane select happens to end up in a VGPR.
Clarify the semantic of the corresponding intrinsic to be that of
the corresponding GLSL: the lane select must be uniform across a
wave front, otherwise results are undefined.
Reviewers: arsenm
Subscribers: kzhuravl, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits
Differential Revision: https://reviews.llvm.org/D32343
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301197
91177308-0d34-0410-b5e6-
96231b3b80d8