Add support of RTM from TSX extension

- Add RTM code generation support throught 3 X86 intrinsics:
  xbegin()/xend() to start/end a transaction region, and xabort() to abort a
  tranaction region



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167573 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/X86Subtarget.cpp

@@ -302,6 +302,10 @@ void X86Subtarget::AutoDetectSubtargetFeatures() {
         HasBMI2 = true;
         ToggleFeature(X86::FeatureBMI2);
       }
+      if (IsIntel && ((EBX >> 11) & 0x1)) {
+        HasRTM = true;
+        ToggleFeature(X86::FeatureRTM);
+      }
     }
   }
 }
@@ -330,6 +334,7 @@ X86Subtarget::X86Subtarget(const std::string &TT, const std::string &CPU,
   , HasLZCNT(false)
   , HasBMI(false)
   , HasBMI2(false)
+  , HasRTM(false)
   , IsBTMemSlow(false)
   , IsUAMemFast(false)
   , HasVectorUAMem(false)