Tested powerpc64le-linux, pushed to trunk.
-- >8 --
Add attributes to the accessors for the global memory resource objects,
to allow the compiler to eliminate redundant calls to them. For example,
multiple calls to std::pmr::new_delete_resource() will always return the
same object, and so the compiler can replace them with a single call.
Ideally we would like adjacent calls to std::pmr::get_default_resource()
to be combined into a single call by the CSE pass. The 'pure' attribute
would permit that. However, the standard requires that calls to
std::pmr::set_default_resource() synchronize with subsequent calls to
std::pmr::get_default_resource(). With 'pure' the DCE pass might
eliminate seemingly redundant calls to std::pmr::get_default_resource().
That might be unsafe, because the caller might be relying on the
associated synchronization. We could use a hypothetical attribute that
allows CSE but not DCE, but we don't have one. So it can't be 'pure'.
Also add [[nodiscard]] to equality operators.
libstdc++-v3/ChangeLog:
* include/std/memory_resource (new_delete_resource): Add
nodiscard, returns_nonnull and const attributes.
(null_memory_resource): Likewise.
(set_default_resource, get_default_resource): Add returns_nonnull
attribute.
(memory_resource::is_equal): Add nodiscard attribute.
(operator==, operator!=): Likewise.
---
libstdc++-v3/include/std/memory_resource | 30 ++++++++++++++++++++----
1 file changed, 25 insertions(+), 5 deletions(-)
diff --git a/libstdc++-v3/include/std/memory_resource
b/libstdc++-v3/include/std/memory_resource
index 4a18d3e8598..88e8abd60fa 100644
--- a/libstdc++-v3/include/std/memory_resource
+++ b/libstdc++-v3/include/std/memory_resource
@@ -74,11 +74,26 @@ namespace pmr
#endif
// Global memory resources
- memory_resource* new_delete_resource() noexcept;
- memory_resource* null_memory_resource() noexcept;
- memory_resource* set_default_resource(memory_resource* __r) noexcept;
- memory_resource* get_default_resource() noexcept
- __attribute__((__returns_nonnull__));
+
+ /// A pmr::memory_resource that uses `new` to allocate memory
+ [[nodiscard, __gnu__::__returns_nonnull__, __gnu__::__const__]]
+ memory_resource*
+ new_delete_resource() noexcept;
+
+ /// A pmr::memory_resource that always throws `bad_alloc`
+ [[nodiscard, __gnu__::__returns_nonnull__, __gnu__::__const__]]
+ memory_resource*
+ null_memory_resource() noexcept;
+
+ /// Replace the default memory resource pointer
+ [[__gnu__::__returns_nonnull__]]
+ memory_resource*
+ set_default_resource(memory_resource* __r) noexcept;
+
+ /// Get the current default memory resource pointer
+ [[__gnu__::__returns_nonnull__]]
+ memory_resource*
+ get_default_resource() noexcept;
// Pool resource classes
struct pool_options;
@@ -111,6 +126,7 @@ namespace pmr
__attribute__((__nonnull__))
{ return do_deallocate(__p, __bytes, __alignment); }
+ [[nodiscard]]
bool
is_equal(const memory_resource& __other) const noexcept
{ return do_is_equal(__other); }
@@ -126,11 +142,13 @@ namespace pmr
do_is_equal(const memory_resource& __other) const noexcept = 0;
};
+ [[nodiscard]]
inline bool
operator==(const memory_resource& __a, const memory_resource& __b) noexcept
{ return &__a == &__b || __a.is_equal(__b); }
#if __cpp_impl_three_way_comparison < 201907L
+ [[nodiscard]]
inline bool
operator!=(const memory_resource& __a, const memory_resource& __b) noexcept
{ return !(__a == __b); }
@@ -369,6 +387,7 @@ namespace pmr
};
template<typename _Tp1, typename _Tp2>
+ [[nodiscard]]
inline bool
operator==(const polymorphic_allocator<_Tp1>& __a,
const polymorphic_allocator<_Tp2>& __b) noexcept
@@ -376,6 +395,7 @@ namespace pmr
#if __cpp_impl_three_way_comparison < 201907L
template<typename _Tp1, typename _Tp2>
+ [[nodiscard]]
inline bool
operator!=(const polymorphic_allocator<_Tp1>& __a,
const polymorphic_allocator<_Tp2>& __b) noexcept
--
2.34.3
