[Bug target/42553] wrong code with -O1

[ubizjak at gmail dot com]

--- Comment #3 from ubizjak at gmail dot com  2010-01-04 16:07 ---
(In reply to comment #2)
 The inline-asm is totally incorrect here ...

Actually, the asm is correct, it is just a couple of volatiles that are
missing. Please see arch/x86/include/asm/bitops.h from linux-2.6 for correct
implementation.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553

[Bug target/42553] wrong code with -O1

[pinskia at gmail dot com]

--- 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-bugzi...@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   0222
 gcc-4.3   0222
 gcc-4.4   2000
 gcc-4.5   0100

  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

[Bug target/42553] wrong code with -O1

[pinskia at gcc dot gnu dot org]

--- Comment #2 from pinskia at gcc dot gnu dot org  2009-12-30 14:33 ---
The inline-asm is totally incorrect here is the corrected version of the
function (note res should be set):
static bool atomic_test_and_reset_bit(unsigned long *v,unsigned long bit) {
  bool res = 0;

  __asm__ __volatile__( btr %2,%1\n
adc $0,%0\n
:+r(res): m(*v)
,r(bit), r(0): flags) ;
  return res ? 1 : 0;
}


-- 

pinskia at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553