From mboxrd@z Thu Jan  1 00:00:00 1970
From: ak@muc.de
To: egcs@cygnus.com
Subject: Poor i386 code from egcs.
Date: Sat, 27 Jun 1998 04:30:00 -0000
Message-id: <19980627132952.28632@kali.lrz-muenchen.de>
X-SW-Source: 1998-06/msg00992.html

Hello,

Given this simple program:
(is it safe to use &tmp after the scope ends? Seems to do no harm in gcc)

#define NUMADDR(x) ({ typeof(x) tmp = (x); &tmp; })

f()
{
	f2(NUMADDR(1));
}

% egcc -v
Reading specs from /pkg/egcs-980605/lib/gcc-lib/i686-pc-linux-gnu/egcs-2.91.34/specs
gcc version egcs-2.91.34 19980605 (gcc2 ss-980502 experimental)

% egcc -O2 -fomit-frame-pointer -S tcadr.c

Results in this assembler code:

.globl f
        .type    f,@function
f:
        subl $4,%esp
        movl $1,(%esp)
        movl %esp,%eax
        pushl %eax           <----- why can't it push %esp directly?
        call f2
        addl $4,%esp
        addl $4,%esp         <------ why not combine them in one addl?
        ret

Especially the double add looks bad on i386 (it would make sense on m68k,
but not on i386 I think) because it is probably a common occurence. It is
not dependent on the ({ }) block, but happens in an ANSI-C equivalent too.

Is it possible to fix it with a peephole optimizer rule?

I believe the push problem could be fixed by some "widening" of constraints
in i386.md, but my understanding is not good enough to do it myself. 


-Andi