Re: ACCUMULATE_OUTGOING_ARGS and the i386

[Joe Buck <jbuck at synopsys dot com>]

>   > What are the tradeoffs involved in ACCUMULATE_OUTGOING_ARGS?  Why
>   > would I not want to implement it for the i386?

Jeff writes:
> Plusses:
> 
>   Stack pointer stays constant...
>   A constant stack pointer makes it a lot easier for gdb to grok frame
>   pointerless code.  This may make it possible to turn on frame pointer
>   elimination by default.
> 
>     1. More efficient prologues & epilogues.
>     2. The compiler gets to use another register.

It seems that #2 would be a big win on the register-poor i386
architecture.  Also, overhead for C++ exceptions should be reduced
substantially, right?

> Minuses:
> 
>   If the architecture has push insns and they're smaller/faster than
>   using reg+d addresses, then ACCUMULATE_OUTGOING_ARGS may be a lose due
>   to the increased cost to save arguments into the stack.  Depends on the
>   relative costs.

Given the other factors, this increased cost might be outweighed by
the benefits, but of course this would have to be measured.  I suspect
that a push might even be slower on the new processors if there are
many separate stack adjustments, but I'm far from an x86 guru.