[PATCH, libstdc++]: Avoid "libsupc++/guard.cc:118:18: warning: variable ‘__p’ set but not used" warning

[Jonathan Wakely]

On 01/07/15 12:22 +0200, Uros Bizjak wrote:
>Hello!
>
>2015-07-01  Uros Bizjak  <ubizjak@gmail.com>
>
>    * libsupc++/guard.cc (__test_and_acquire): Use __p after __atomic_load
>    to avoid unused variable warning.
>    (__set_and_release): Use __p after __atomic_store to avoid unused
>    variable warning.
>
>Bootstrapped and regression tested on x86_64-linux-gnu.
>
>OK for mainline?

Yes, OK, although I was wondering if this should really be fixed in
the front end, the warning is spurious, isn't it? __p is not unused,
because the load is done through it.

>Index: libsupc++/guard.cc
>===================================================================
>--- libsupc++/guard.cc	(revision 225221)
>+++ libsupc++/guard.cc	(working copy)
>@@ -117,6 +117,7 @@ __test_and_acquire (__cxxabiv1::__guard *g)
>   unsigned char __c;
>   unsigned char *__p = reinterpret_cast<unsigned char *>(g);
>   __atomic_load (__p, &__c,  __ATOMIC_ACQUIRE);
>+  (void) __p;
>   return _GLIBCXX_GUARD_TEST(&__c);
> }
> #  define _GLIBCXX_GUARD_TEST_AND_ACQUIRE(G) __test_and_acquire (G)
>@@ -132,6 +133,7 @@ __set_and_release (__cxxabiv1::__guard *g)
>   unsigned char *__p = reinterpret_cast<unsigned char *>(g);
>   unsigned char val = 1;
>   __atomic_store (__p, &val, __ATOMIC_RELEASE);
>+  (void) __p;
> }
> #  define _GLIBCXX_GUARD_SET_AND_RELEASE(G) __set_and_release (G)
> # endif