[PATCH 1/3] Atomic __platform_wait: accept any 32-bit type, not just int

[Thiago Macieira]

The kernel doesn't care what we store in those 32 bits, only that they are
comparable. This commit adds:
 * pointers and long on 32-bit architectures
 * unsigned
 * untyped enums and typed enums on int & unsigned int
 * float

We're not using FUTEX_OP anywhere today. The kernel reserves 4 bits for
this field but has only used 6 values so far, so it can be extended to
unsigned compares in the future, if needed.

libstdc++-v3/ChangeLog:

        * include/bits/atomic_wait.h: Update __platform_wait_uses_type
---
 libstdc++-v3/include/bits/atomic_wait.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index 424fccbe4c5..4b4573df691 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -65,7 +65,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _Tp>
       inline constexpr bool __platform_wait_uses_type
 #ifdef _GLIBCXX_HAVE_LINUX_FUTEX
-	= is_same_v<remove_cv_t<_Tp>, __platform_wait_t>;
+	= sizeof(_Tp) == sizeof(__platform_wait_t) &&
+	  alignof(_Tp) >= alignof(__platform_wait_t);
 #else
 	= false;
 #endif
@@ -91,13 +92,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _Tp>
       void
-      __platform_wait(const _Tp* __addr, __platform_wait_t __val) noexcept
+      __platform_wait(const _Tp* __addr, _Tp __val) noexcept
       {
 	for(;;)
 	  {
 	    auto __e = syscall (SYS_futex, static_cast<const void*>(__addr),
 				  static_cast<int>(__futex_wait_flags::__wait_private),
-				    __val, nullptr);
+				  static_cast<__platform_wait_t>(__val), nullptr);
 	    if (!__e || errno == EAGAIN)
 	      break;
 	    else if (errno != EINTR)
-- 
2.30.1