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From: "pinskia at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/42553] wrong code with -O1 Date: Wed, 30 Dec 2009 13:15:00 -0000 [thread overview] Message-ID: <20091230131453.19538.qmail@sourceware.org> (raw) In-Reply-To: <bug-42553-5724@http.gcc.gnu.org/bugzilla/> ------- Comment #1 from pinskia at gmail dot com 2009-12-30 13:14 ------- Subject: Re: New: wrong code with -O1 Sent from my iPhone On Dec 30, 2009, at 7:56 AM, "debian-gcc at lists dot debian dot org" <gcc-bugzilla@gcc.gnu.org > wrote: > current trunk/branches on x86_64-linux-gnu. return values with > different > compilers and different optimizations: > > -O0 -O1 -O2 -O3 > gcc-4.1 0 2 2 2 > gcc-4.3 0 2 2 2 > gcc-4.4 2 0 0 0 > gcc-4.5 0 1 0 0 > > Matthias > > #include <stdbool.h> > #include <stdio.h> > > static bool atomic_test_and_reset_bit(unsigned long *v,unsigned long > bit) { > bool res; > > __asm__ __volatile__( "btr %2,%1\n" > "adc $0,%0\n" > :"=r"(res), "=m"(*v) > :"r"(bit), "r"(0)) ; > return res ? 1 : 0; This inline-asm looks wrong. Because it says *v is always overriden. So if that function is inlined, flags down below does not have to be set before it. > } > > int main(void) > { > unsigned long flags = 0; > int j; > > j = atomic_test_and_reset_bit(&flags, 2); > > printf("%d\n", j); > > return 0; > } > > > -- > Summary: wrong code with -O1 > Product: gcc > Version: 4.4.3 > Status: UNCONFIRMED > Severity: normal > Priority: P3 > Component: target > AssignedTo: unassigned at gcc dot gnu dot org > ReportedBy: debian-gcc at lists dot debian dot org > GCC target triplet: x86_64-linux-gnu > > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553 > -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553
next prev parent reply other threads:[~2009-12-30 13:15 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2009-12-30 12:57 [Bug target/42553] New: " debian-gcc at lists dot debian dot org 2009-12-30 13:14 ` Andrew Pinski 2009-12-30 13:15 ` pinskia at gmail dot com [this message] 2009-12-30 14:33 ` [Bug target/42553] " pinskia at gcc dot gnu dot org 2010-01-04 16:07 ` ubizjak at gmail dot com
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