Implement atomicrmw operations in 32 and 64 bits for SPARCv9.

These all use the compare-and-swap CASA/CASXA instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199975 91177308-0d34-0410-b5e6-96231b3b80d8
[X86] Prevent the creation of redundant ops for sadd and ssub with overflow.

This commit teaches the X86 backend to create the same X86 instructions when it
lowers an sadd/ssub with overflow intrinsic and a conditional branch that uses
that overflow result. This allows SelectionDAG to recognize and remove one of
the redundant operations.

This fixes <rdar://problem/15874016> and <rdar://problem/15661073>.

Reviewed by Nadav

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199976 91177308-0d34-0410-b5e6-96231b3b80d8