[Bug c/39403] Excessive optimization issue

[casmyu at gmail dot com]

--- Comment #3 from casmyu at gmail dot com  2009-03-10 01:23 ---
Hi:
I have changed the code as you said, but it is more error now.

  1 #include 
  2
  3 int main()
  4 {
  5 char src[30] = {"This is a test message.\n"};
  6 char dst[30];
  7 int len = 25;
  8
  9 __asm__ __volatile__(
 10 "cld\n\t"
 11 "rep movsb"
 12 :
 13 //  : "(src), "D"(dst), "c"(len)
 14 : "+c"(len), "+D"(dst), "+S"(src)
 15 );
 16 printf("%s\t%d\n", dst, len);
 17 return 0;
 18 }

[root][~]# gcc -O2 -o bugtest bugtest.c
bugtest.c: In function ¡®main¡¯:
bugtest.c:15: error: input operand constraint contains ¡®+¡¯
bugtest.c:15: error: input operand constraint contains ¡®+¡¯
bugtest.c:15: error: input operand constraint contains ¡®+¡¯
bugtest.c:9: error: input operand constraint contains ¡®+¡¯
bugtest.c:9: error: input operand constraint contains ¡®+¡¯
bugtest.c:9: error: input operand constraint contains ¡®+¡¯

Please help to re-check this issue.
Thank you!

(In reply to comment #2)
> Subject: Re:  Excessive optimization issue
> 
> 
> 
> Sent from my iPhone
> 
> On Mar 9, 2009, at 8:36 AM, "rguenth at gcc dot gnu dot org"
>   > wrote:
> 
> >
> >
> > --- Comment #1 from rguenth at gcc dot gnu dot org  2009-03-09  
> > 15:36 ---
> > You need to specify that the registers are clobbered by the asm.   
> > The only
> > way to do that is to use output constraints ("+D", "+c", etc.) on  
> > proper
> > temporaries.
> >
> >  int lent = len;
> >  char *dstt = dst;
> >  char *srct = src;
> >  __asm__ __volatile__(
> >   "cld\n\t"
> >   "rep movsb"
> >   : "+c" (lent), "+D"(dstt), "+S"(src)
> >  );
> > Otherwise GCC thinks the registers still hold the original value.
> 
> Oh and mark this inline-ask as clobbering memory.
> 
> >
> >
> >
> > -- 
> >
> > rguenth at gcc dot gnu dot org changed:
> >
> >   What|Removed |Added
> > --- 
> > --- 
> > --
> > Status|UNCONFIRMED |RESOLVED
> > Resolution||INVALID
> >
> >
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403
> >
> 


-- 

casmyu at gmail dot com changed:

   What|Removed |Added

 CC||casmyu at gmail dot com
 Status|RESOLVED|UNCONFIRMED
 Resolution|INVALID |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403

[Bug c/39403] Excessive optimization issue

[pinskia at gmail dot com]

--- Comment #2 from pinskia at gmail dot com  2009-03-09 15:57 ---
Subject: Re:  Excessive optimization issue



Sent from my iPhone

On Mar 9, 2009, at 8:36 AM, "rguenth at gcc dot gnu dot org"
 wrote:

>
>
> --- Comment #1 from rguenth at gcc dot gnu dot org  2009-03-09  
> 15:36 ---
> You need to specify that the registers are clobbered by the asm.   
> The only
> way to do that is to use output constraints ("+D", "+c", etc.) on  
> proper
> temporaries.
>
>  int lent = len;
>  char *dstt = dst;
>  char *srct = src;
>  __asm__ __volatile__(
>   "cld\n\t"
>   "rep movsb"
>   : "+c" (lent), "+D"(dstt), "+S"(src)
>  );
> Otherwise GCC thinks the registers still hold the original value.

Oh and mark this inline-ask as clobbering memory.

>
>
>
> -- 
>
> rguenth at gcc dot gnu dot org changed:
>
>   What|Removed |Added
> --- 
> --- 
> --
> Status|UNCONFIRMED |RESOLVED
> Resolution||INVALID
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403
>


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403

Re: [Bug c/39403] Excessive optimization issue

[Andrew Thomas Pinski]

Sent from my iPhone

On Mar 9, 2009, at 8:36 AM, "rguenth at gcc dot gnu dot org" > wrote:





--- Comment #1 from rguenth at gcc dot gnu dot org  2009-03-09  
15:36 ---
You need to specify that the registers are clobbered by the asm.   
The only
way to do that is to use output constraints ("+D", "+c", etc.) on  
proper

temporaries.

 int lent = len;
 char *dstt = dst;
 char *srct = src;
 __asm__ __volatile__(
  "cld\n\t"
  "rep movsb"
  : "+c" (lent), "+D"(dstt), "+S"(src)
 );
Otherwise GCC thinks the registers still hold the original value.


Oh and mark this inline-ask as clobbering memory.





--

rguenth at gcc dot gnu dot org changed:

  What|Removed |Added
--- 
--- 
--

Status|UNCONFIRMED |RESOLVED
Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403

[Bug c/39403] Excessive optimization issue

[rguenth at gcc dot gnu dot org]

--- Comment #1 from rguenth at gcc dot gnu dot org  2009-03-09 15:36 ---
You need to specify that the registers are clobbered by the asm.  The only
way to do that is to use output constraints ("+D", "+c", etc.) on proper
temporaries.

  int lent = len;
  char *dstt = dst;
  char *srct = src;
  __asm__ __volatile__(
   "cld\n\t"
   "rep movsb"
   : "+c" (lent), "+D"(dstt), "+S"(src)
  );

Otherwise GCC thinks the registers still hold the original value.


-- 

rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403