[Bug c/39403] Excessive optimization issue

["casmyu at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

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------- 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 <stdio.h>
  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"
> <gcc-bugzilla@gcc.gnu.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