https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62109
--- Comment #4 from David <gccbugzilla at limegreensocks dot com> --- (In reply to Mikael Pettersson from comment #3) > Do you have a test case which fails without your patch? I do not. But this is a "by definition" thing. This instruction is intended to emulate the Windows InterlockedCompareExchange instruction (see the comments above the code). And all Windows Interlocked* instructions perform an implicit compiler barrier. After all, it does no good for the 'lock' prefix to prevent the processor from re-ordering instructions if the compiler does it while building the code. Moving loads or stores past this statement makes a mess of thread synchronization. That said, this instruction was only intended to be used on Win95 (neither NT nor Win98 need it). Not exactly a common platform these days. But it's possible someone is still using this, or will copy this asm block for their own use, so it should still be correct.
