[committed] libstdc++: Avoid use of hardware interference non-constant [PR102377]

[committed] libstdc++: Avoid use of hardware interference non-constant [PR102377]

[Jonathan Wakely]

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libstdc++-v3/ChangeLog:

	PR libstdc++/102377
	* include/bits/atomic_wait.h (__waiter_pool_base:_S_align):
	Hardcode to 64 instead of using non-constant constant.

Tested x86_64-linux. Committed to trunk.


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commit 0e90799071ee78f712f3b58fca7000bc0a258ade
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Oct 7 18:28:04 2021

    libstdc++: Avoid use of hardware interference non-constant [PR102377]
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/102377
            * include/bits/atomic_wait.h (__waiter_pool_base:_S_align):
            Hardcode to 64 instead of using non-constant constant.

diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index 35c92644146..2ac07ccd05e 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -190,11 +190,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     struct __waiter_pool_base
     {
-#ifdef __cpp_lib_hardware_interference_size
-    static constexpr auto _S_align = hardware_destructive_interference_size;
-#else
-    static constexpr auto _S_align = 64;
-#endif
+      // Don't use std::hardware_destructive_interference_size here because we
+      // don't want the layout of library types to depend on compiler options.
+      static constexpr auto _S_align = 64;
 
       alignas(_S_align) __platform_wait_t _M_wait = 0;