[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.

(Re-commit of r227728)

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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227752 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/TargetFrameLoweringImpl.cpp

@@ -42,3 +42,8 @@ int TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF,
   FrameReg = RI->getFrameRegister(MF);
   return getFrameIndexOffset(MF, FI);
 }
+
+bool TargetFrameLowering::needsFrameIndexResolution(
+    const MachineFunction &MF) const {
+  return MF.getFrameInfo()->hasStackObjects();
+}