[Bug target/34888] Stack patterns for AVR not optimal

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34888

--- Comment #4 from Richard Henderson <rth at gcc dot gnu.org> 2011-08-02 21:10:51 UTC ---
Created attachment 24897
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24897
Optimize pop-all

The proposed patch for PR49864 introduces REG_ARGS_SIZE.
This records a (normally) non-negative number of bytes
that have been pushed for arguments.

Post-reload, if we see a (mov sp reg) insn that says that
it's resetting the stack height, under a (common) set of
conditions we can transform that to (mov sp fp) and let
the previous (mov reg sp) (add reg N) insns be deleted as
dead code.

This reduces that common case to 4 insns instead of 9.