Merging r339945:

Merging r339945:
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r339945 | ctopper | 2018-08-16 23:54:02 +0200 (Thu, 16 Aug 2018) | 9 lines

[X86] In EFLAGS copy pass, don't emit EXTRACT_SUBREG instructions since we're after peephole

Normally the peephole pass converts EXTRACT_SUBREG to COPY instructions. But we're after peephole so we can't rely on it to clean these up.

To fix this, the eflags pass now emits a COPY with a subreg input.

I also noticed that in 32-bit mode we need to constrain the input to the copy to ensure the subreg is valid. Otherwise we'll fail verify-machineinstrs

Differential Revision: https://reviews.llvm.org/D50656
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_70@339999 91177308-0d34-0410-b5e6-96231b3b80d8