[X86] Add CMPXCHG8B feature flag. Set it for all CPUs except i386/i486 including 'generic'. Disable use of CMPXCHG8B when this flag isn't set.
CMPXCHG8B was introduced on i586/pentium generation.
If its not enabled, limit the atomic width to 32 bits so the AtomicExpandPass will expand to lib calls. Unclear if we should be using a different limit for other configs. The default is 1024 and experimentation shows that using an i256 atomic will cause a crash in SelectionDAG.
Differential Revision: https://reviews.llvm.org/D59576
llvm-svn: 356631
diff --git a/llvm/lib/Support/Host.cpp b/llvm/lib/Support/Host.cpp
index 52e7080..6936270 100644
--- a/llvm/lib/Support/Host.cpp
+++ b/llvm/lib/Support/Host.cpp
@@ -1264,6 +1264,7 @@
getX86CpuIDAndInfo(1, &EAX, &EBX, &ECX, &EDX);
+ Features["cx8"] = (EDX >> 8) & 1;
Features["cmov"] = (EDX >> 15) & 1;
Features["mmx"] = (EDX >> 23) & 1;
Features["fxsr"] = (EDX >> 24) & 1;