From: Georg-Johann Lay <avr@gjlay.de>
To: Michael Walle <michael@walle.cc>
Cc: gcc@gcc.gnu.org
Subject: Re: libgcc: strange optimization
Date: Mon, 01 Aug 2011 20:51:00 -0000 [thread overview]
Message-ID: <4E37116F.1050608@gjlay.de> (raw)
In-Reply-To: <201108012230.29989.michael@walle.cc>
Michael Walle schrieb:
> Hi list,
>
> consider the following test code:
> static void inline f1(int arg)
> {
> register int a1 asm("r8") = 10;
> register int a2 asm("r1") = arg;
>
> asm("scall" : : "r"(a1), "r"(a2));
> }
>
> void f2(int arg)
> {
> f1(arg >> 10);
> }
>
>
> If you compile this code with 'lm32-gcc -O1 -S -c test.c' (see end of this
> email), the a1 = 10; assignment is optimized away.
Your asm has no output operands and no side effects, with more
aggressive optimization the whole ask would disappear.
What you want is maybe something like
asm volatile ("scall" : : "r"(a1), "r"(a2));
Johann
next prev parent reply other threads:[~2011-08-01 20:51 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-01 20:30 Michael Walle
2011-08-01 20:51 ` Georg-Johann Lay [this message]
2011-08-01 21:14 ` Michael Walle
2011-08-02 6:47 ` Georg-Johann Lay
2011-08-02 6:29 ` Hans-Peter Nilsson
2011-08-01 21:30 ` Richard Henderson
2011-08-02 6:37 ` Hans-Peter Nilsson
2011-08-02 8:49 ` Mikael Pettersson
2011-08-02 9:47 ` Richard Guenther
2011-08-02 10:02 ` Georg-Johann Lay
2011-08-02 10:11 ` Richard Guenther
2011-08-02 10:55 ` Michael Walle
2011-08-02 12:06 ` Mikael Pettersson
2011-08-02 12:23 ` Richard Guenther
2011-08-02 12:36 ` Georg-Johann Lay
2011-08-02 12:54 ` Hans-Peter Nilsson
2011-08-02 13:09 ` Richard Guenther
2011-08-02 13:16 ` Hans-Peter Nilsson
2011-08-03 4:59 ` Miles Bader
2011-08-02 13:23 ` Ian Lance Taylor
2011-08-02 13:42 ` Richard Guenther
2011-08-02 14:35 ` Ian Lance Taylor
2011-08-03 9:12 ` Ulrich Weigand
2011-08-03 9:51 ` Georg-Johann Lay
2011-08-03 10:04 ` Richard Guenther
2011-08-03 13:27 ` Michael Matz
2011-08-03 14:02 ` Richard Guenther
2011-08-03 14:55 ` Georg-Johann Lay
2011-08-03 15:05 ` Richard Henderson
2011-08-04 0:20 ` Hans-Peter Nilsson
2011-08-04 7:29 ` Andreas Schwab
2011-08-04 13:04 ` Hans-Peter Nilsson
2011-08-04 9:51 ` Andrew Haley
2011-08-04 9:52 ` Richard Guenther
2011-08-04 11:11 ` Andrew Haley
2011-08-04 11:20 ` Richard Guenther
2011-08-04 14:46 ` Andrew Haley
2011-08-06 15:00 ` Paolo Bonzini
2011-08-08 8:06 ` Richard Guenther
2011-08-08 10:59 ` Paolo Bonzini
2011-08-02 16:03 ` Richard Henderson
2011-08-02 20:10 ` Richard Guenther
2011-08-02 17:21 ` Georg-Johann Lay
2011-08-09 16:55 ` Richard Earnshaw
2011-08-09 17:24 ` Ulrich Weigand
2011-08-09 19:48 ` Hans-Peter Nilsson
2011-08-10 0:40 ` Hans-Peter Nilsson
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