[ported from trunk r165339, adjusted to apply to linux-atomic.c
 in config/m68k/; the __builtin_expect change is excluded <mikpe@it.uu.se>]

Date: Mon, 11 Oct 2010 17:42:04 -0400
From: John David Anglin <dave at hiauly1 dot hia dot nrc dot ca>
Subject: Re: [committed] Update config/pa/linux-atomic.c and enable sync tests on hppa-linux
List-Archive: <http://gcc.gnu.org/ml/gcc-patches/>

On Wed, 11 Aug 2010, Richard Henderson wrote:

> FWIW, I had a browse through this file and it's a bit off.  E.g.:
> 
> > __sync_val_compare_and_swap_4 (int *ptr, int oldval, int newval)
> > {
> >   int actual_oldval, fail;
> >     
> >   while (1)
> >     {
> >       actual_oldval = *ptr;
> > 
> >       if (oldval != actual_oldval)
> >         return actual_oldval;
> > 
> >       fail = __kernel_cmpxchg (actual_oldval, newval, ptr);
> >   
> >       if (!fail)
> >         return oldval;
> >     }
> > }
> 
> This should not be returning the OLDVAL that the user passed,
> it should be returning the lws_ret that the kernel returned.
> 
> This is because the user of __sync_val_c_a_s wants avoid the
> reload of the value, like so (from libgomp/iter.c):

I adjusted the returns per your suggestion.  Does this look right?

I have had this in my hppa-linux build trees for some time and haven't
seen and regressions.

Thanks for looking over the original patch.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)

gcc/

2010-10-11  John David Anglin  <dave.anglin@nrc-cnrc.gc.ca>

	* config/pa/linux-atomic.c (__sync_val_compare_and_swap_4): Return
	actual_oldval.  Use __builtin_expect.
	(SUBWORD_VAL_CAS): Likewise.

--- gcc-4.6.3/gcc/config/m68k/linux-atomic.c.~1~	2012-06-18 22:48:07.000000000 +0200
+++ gcc-4.6.3/gcc/config/m68k/linux-atomic.c	2012-06-18 22:54:25.000000000 +0200
@@ -183,7 +183,7 @@ __sync_val_compare_and_swap_4 (int *ptr,
       fail = __kernel_cmpxchg (actual_oldval, newval, ptr);
   
       if (__builtin_expect (!fail, 1))
-        return oldval;
+        return actual_oldval;
     }
 }
 
@@ -213,7 +213,7 @@ __sync_val_compare_and_swap_4 (int *ptr,
 				 wordptr);				\
 									\
       if (__builtin_expect (!fail, 1))                                  \
-          return oldval;						\
+          return (actual_oldval & mask) >> shift;			\
       }									\
   }