[mips][atomics] Fix partword atomic binary operation implementation
Currently Mips::emitAtomicBinaryPartword() does not properly respect the
width of pointers. For MIPS64 this causes the memory address that the ll/sc
sequence uses to be truncated. At runtime this causes a segmentation fault.
This can be fixed by applying similar changes as r266204, so that a full 64bit
pointer is loaded.
Reviewers: dsanders
Differential Review: http://reviews.llvm.org/D19651
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267900
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