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

[Nadav Rotem]

Hi Michael, 

Overall it looks really good.  Did you measure the performance of this patch on the llvm test suite?  Do you know if this transformation is beneficial for all recent x86 processors?  If it is not then we can enable it for specific processors. 

Also, can you use DenseMap instead of std::map?

Thanks,
Nadav

http://reviews.llvm.org/D6503