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Allow code motion (and thus folding) for atomic (but unordered) memory operands

Authored by reames on Mar 14 2019, 10:20 AM.

Description

Allow code motion (and thus folding) for atomic (but unordered) memory operands

Building on the work done in D57601, now that we can distinguish between atomic and volatile memory accesses, go ahead and allow code motion of unordered atomics. As seen in the diffs, this allows much better folding of memory operations into using instructions. (Mostly done by the PeepholeOpt pass.)

Note: I have not reviewed all callers of hasOrderedMemoryRef since one of them - isSafeToMove - is very widely used. I'm relying on the documented semantics of each method to judge correctness.

Differential Revision: https://reviews.llvm.org/D59345

llvm-svn: 356170