Merging r324422:

Merging r324422:
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r324422 | efriedma | 2018-02-07 00:00:17 +0100 (Wed, 07 Feb 2018) | 16 lines

[LivePhysRegs] Fix handling of return instructions.

See D42509 for the original version of this.

Basically, there are two significant changes to behavior here:

- addLiveOuts always adds all pristine registers (even if a block has
no successors).
- addLiveOuts and addLiveOutsNoPristines always add all callee-saved
registers for return blocks (including conditional return blocks).

I cleaned up the functions a bit to make it clear these properties hold.

Differential Revision: https://reviews.llvm.org/D42655

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@324466 91177308-0d34-0410-b5e6-96231b3b80d8