Re: dwarf2/ACCUMULATE_OUTGOING_ARGS fix

[Jan Hubicka <jh at suse dot cz>]

>   In message <20010102200705.H6101@atrey.karlin.mff.cuni.cz>you write:
>   > Hi
>   > The final.c assumes that ACCUMULATE_OUTGOING_ARGS hosts never modify
>   > stack pointer in the function body.  This is not quite true for i386
>   > that may call pascal functions and modify stack pointer in few
>   > other cases as well.
> Under precisely what conditions can code still modify the stack pointer
> when ACCUMULATE_OUTGOING_ARGS is true?  And I'm curious why calling pascal
> routines requires modification of the stack pointer.
Simply because the i386 "pascal" convention makes function to deallocate the
stack after return.  This needs to be handled with -maccumulate-outgoing-args
by adjusting stack back after the return.

Later the stack adjustments may be moved futher into code, so they cause
failures in the tests explicitly constructed for this case.

But the real motivation for this patch was different - I was investigating
possibility of using dwarf2 unwind info as the only way to unwind stack on
x86_64 (by dropping the i386 base pointer) and I needed to measure how large
code bloat it causes to emit explicit unwind info for each instruction.

Enabling -maccumulate-outgoing-args caused important improvements, since gcc
dropped updating the CFA offsets in the epilogues, that still do use pop
instruction.

Honza
> 
> jeff