Use the 'target-features' and 'target-cpu' attributes to reset the subtarget features.

If two functions require different features (e.g., `-mno-sse' vs. `-msse') then
we want to honor that, especially during LTO. We can do that by resetting the
subtarget's features depending upon the 'target-feature' attribute.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175314 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetSubtargetInfo.h

@@ -19,6 +19,7 @@
 
 namespace llvm {
 
+class MachineFunction;
 class MachineInstr;
 class SDep;
 class SUnit;
@@ -73,6 +74,9 @@ public:
   // the latency of a schedule dependency.
   virtual void adjustSchedDependency(SUnit *def, SUnit *use,
                                      SDep& dep) const { }
+
+  /// \brief Reset the features for the subtarget.
+  virtual void resetSubtargetFeatures(const MachineFunction *MF) { }
 };
 
 } // End llvm namespace