[committed] libstdc++: Fix __thread_yield for non-gthreads targets

[Jonathan Wakely]

On 15/02/21 16:13 +0000, Jonathan Wakely wrote:
>The __gthread_yield() function is only defined for gthreads targets, so
>check _GLIBCXX_HAS_GTHREADS before using it.
>
>Also reorder __thread_relax and __thread_yield so that the former can
>use the latter instead of repeating the same preprocessor checks.
>
>libstdc++-v3/ChangeLog:
>
>	* include/bits/atomic_wait.h (__thread_yield()): Check
>	_GLIBCXX_HAS_GTHREADS before using __gthread_yield.
>	(__thread_relax()): Use __thread_yield() instead of repeating
>	the preprocessor checks for __gthread_yield.



>--- a/libstdc++-v3/include/bits/atomic_wait.h
>+++ b/libstdc++-v3/include/bits/atomic_wait.h
>@@ -213,24 +213,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       { _M_w._M_do_wait(_M_version); }
>     };
>
>-    inline void
>-    __thread_relax() noexcept
>-    {
>-#if defined __i386__ || defined __x86_64__
>-      __builtin_ia32_pause();
>-#elif defined _GLIBCXX_USE_SCHED_YIELD
>-      __gthread_yield();
>-#endif
>-    }
>-
>     inline void
>     __thread_yield() noexcept
>     {
>-#if defined _GLIBCXX_USE_SCHED_YIELD
>+#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
>      __gthread_yield();
> #endif
>     }
>
>+    inline void
>+    __thread_relax() noexcept
>+    {
>+#if defined __i386__ || defined __x86_64__
>+      __builtin_ia32_pause();
>+#else
>+      __gthread_yield();

As I said in the ChangeLog, this was supposed to be changed from
__gthread_yield to __thread_yield. Fixed by this patch.

Tested powerpc64le-linux. Committed to trunk.

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