[PATCH] D58290: Convert atomicrmws to xchg or store where legal

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
reames added reviewers: jfb, spatel, qcolombet.
Herald added subscribers: jdoerfert, bollu, mcrosier.

Implement two more transforms of atomicrmw in InstCombine.

1. We can convert an atomicrmw which produces a known value in memory into an xchg instead.
2. We can convert an atomicrmw xchg w/o users into a store for some orderings.


https://reviews.llvm.org/D58290

Files:
  lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp
  test/Transforms/InstCombine/atomicrmw.ll

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