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5335b49f96
We would emit a libcall for a 64-bit atomic on x86 after SVN r212119. This was due to the misuse of hasCmpxchg16 to indicate if cmpxchg8b was supported on a 32-bit target. They were added at different times and would result in the border condition being mishandled. This fixes the border case to emit the cmpxchg8b instruction for 64-bit atomic operations on x86 at the cost of restoring a long-standing bug in the codegen. We emit a cmpxchg8b on all x86 targets even where the CPU does not support this instruction (pre-Pentium CPUs). Although this bug should be fixed, this was present prior to SVN r212119 and this change, so this is not really introducing a regression. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212956 91177308-0d34-0410-b5e6-96231b3b80d8
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