[PATCH] D11749: [X86] When optimizing for size, use POP for small post-call stack clean-up

[Michael Kuperstein]

mkuper created this revision.
mkuper added reviewers: rnk, majnemer.
mkuper added a subscriber: llvm-commits.

When optimizing for size, replace "addl $4, %esp" and "addl $8, %esp" following a call by one or two pops, respectively.

This patch doesn't try to do it in general, but only when the stack adjustment immediately follows a call - which is the most common case.
That allows taking a short-cut when trying to find a free register to pop into, instead of a full-blown liveness check. If the adjustment immediately follows a call, then every register the call clobbers but doesn't define should be dead at that point, and can be used. 


http://reviews.llvm.org/D11749

Files:
  lib/Target/X86/X86FrameLowering.cpp
  lib/Target/X86/X86FrameLowering.h
  test/CodeGen/X86/fold-push.ll
  test/CodeGen/X86/pop-stack-cleanup.ll

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