Merging r359883:

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r359883 | arsenm | 2019-05-03 06:42:56 -0700 (Fri, 03 May 2019) | 6 lines

AMDGPU: Fix incorrect commute with sub when folding immediates

When a fold of an immediate into a sub/subrev required shrinking the
instruction, the wrong VOP2 opcode was used. This was using the VOP2
equivalent of the original instruction, not the commuted instruction
with the inverted opcode.
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llvm-svn: 362161

Author: arsenm