New approach to r136737: insert the necessary fences for atomic ops in platform-independent code, since a bunch of platforms (ARM, Mips, PPC, Alpha are the relevant targets here) need to do essentially the same thing.

I think this completes the basic CodeGen for atomicrmw and cmpxchg.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136813 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index ff4f199..78a75f9 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -401,6 +401,8 @@
   if (PPCSubTarget.isDarwin())
     setPrefFunctionAlignment(4);
 
+  setInsertFencesForAtomic(true);
+
   computeRegisterProperties();
 }