MFC r246858:

MFC r246858:

Pull in r175057 from upstream llvm trunk:

  X86: Disable generation of rep;movsl when %esi is used as a base pointer.

  This happens when there is both stack realignment and a dynamic alloca in the
  function. If we overwrite %esi (rep;movsl uses fixed registers) we'll lose the
  base pointer and the next register spill will write into oblivion.

  Fixes PR15249 and unbreaks firefox on i386/freebsd. Mozilla uses dynamic allocas
  and freebsd a 4 byte stack alignment.

git-svn-id: svn://svn.freebsd.org/base/stable/9@247156 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f