[X86] Convert esp-relative movs of function arguments to pushes, step 2

This moves the transformation introduced in r223757 into a separate MI pass.
This allows it to cover many more cases (not only cases where there must be a 
reserved call frame), and perform rudimentary call folding. It still doesn't 
have a heuristic, so it is enabled only for optsize/minsize, with stack 
alignment <= 8, where it ought to be a fairly clear win.

Differential Revision: http://reviews.llvm.org/D6789

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227728 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetFrameLowering.h

@@ -193,6 +193,11 @@ public:
     return hasReservedCallFrame(MF) || hasFP(MF);
   }
 
+  // needsFrameIndexResolution - Do we need to perform FI resolution for
+  // this function. Normally, this is required only when the function
+  // has any stack objects. However, targets may want to override this.
+  virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
+
   /// getFrameIndexOffset - Returns the displacement from the frame register to
   /// the stack frame of the specified index.
   virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;