[PATCH] [X86] Convert esp-relative movs of function arguments to pushes, step 1

[Michael Kuperstein]

Hi nadav, delena, eliben,

I've started working on using pushes instead of esp-relative movs to pass function arguments.
The main motivation is code size (e.g. 2 bytes instead of 7 to pass an 8-bit immediate), but it some cases it is also faster.

This is just the first step, that handles the simplest case:
1) x86-32 calling convention, everything is passed through the stack.
2) There is no reserved frame (for x86 this happens is there is a dynamic stack allocation in the caller).

Does this look reasonably sane?

http://reviews.llvm.org/D6503

Files:
  lib/Target/X86/X86FrameLowering.cpp
  lib/Target/X86/X86FrameLowering.h
  test/CodeGen/X86/force-align-stack-alloca.ll
  test/CodeGen/X86/inalloca-ctor.ll
  test/CodeGen/X86/inalloca-invoke.ll
  test/CodeGen/X86/inalloca-stdcall.ll
  test/CodeGen/X86/mem-intrin-base-reg.ll
  test/CodeGen/X86/movtopush.ll
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