[PATCH] libstdc++: Define macro before it is first checked

[Jonathan Wakely <jwakely@redhat.com>]

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Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/atomic_wait.h (_GLIBCXX_HAVE_PLATFORM_WAIT):
	Define before first attempt to check it.

Tested x86_64-linux and powerpc64-linux, not committed yet.

I think we need this, otherwise __platform_wait_uses_type<T> is false
for all T.



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commit 9b8a78b5c923efd2f9d10eaed3bfd43dd6a91fe3
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Aug 31 15:51:09 2021

    libstdc++: Define macro before it is first checked
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/atomic_wait.h (_GLIBCXX_HAVE_PLATFORM_WAIT):
            Define before first attempt to check it.

diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index 07bb744d822..64b71e408eb 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -56,9 +56,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   namespace __detail
   {
 #ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+#define _GLIBCXX_HAVE_PLATFORM_WAIT 1
     using __platform_wait_t = int;
     static constexpr size_t __platform_wait_alignment = 4;
 #else
+// define _GLIBCX_HAVE_PLATFORM_WAIT and implement __platform_wait()
+// and __platform_notify() if there is a more efficient primitive supported
+// by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than
+// a mutex/condvar based wait.
     using __platform_wait_t = uint64_t;
     static constexpr size_t __platform_wait_alignment
       = __alignof__(__platform_wait_t);
@@ -70,7 +75,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #ifdef _GLIBCXX_HAVE_PLATFORM_WAIT
       = is_scalar_v<_Tp>
 	&& ((sizeof(_Tp) == sizeof(__detail::__platform_wait_t))
-	&& (alignof(_Tp*) >= __platform_wait_alignment));
+	&& (alignof(_Tp*) >= __detail::__platform_wait_alignment));
 #else
       = false;
 #endif
@@ -78,7 +83,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   namespace __detail
   {
 #ifdef _GLIBCXX_HAVE_LINUX_FUTEX
-#define _GLIBCXX_HAVE_PLATFORM_WAIT 1
     enum class __futex_wait_flags : int
     {
 #ifdef _GLIBCXX_HAVE_LINUX_FUTEX_PRIVATE
@@ -118,11 +122,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		 static_cast<int>(__futex_wait_flags::__wake_private),
 		 __all ? INT_MAX : 1);
       }
-#else
-// define _GLIBCX_HAVE_PLATFORM_WAIT and implement __platform_wait()
-// and __platform_notify() if there is a more efficient primitive supported
-// by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than
-// a mutex/condvar based wait
 #endif
 
     inline void
@@ -192,9 +191,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct __waiter_pool_base
     {
 #ifdef __cpp_lib_hardware_interference_size
-    static constexpr auto _S_align = hardware_destructive_interference_size;
+      static constexpr auto _S_align = hardware_destructive_interference_size;
 #else
-    static constexpr auto _S_align = 64;
+      static constexpr auto _S_align = 64;
 #endif
 
       alignas(_S_align) __platform_wait_t _M_wait = 0;