From 5c2d703e6d6d47f41635ca4df06c555010462081 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Tue, 17 May 2022 15:14:39 +0100 Subject: libstdc++: Add attributes to functions in 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 4a18d3e..88e8abd 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 + [[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 + [[nodiscard]] inline bool operator!=(const polymorphic_allocator<_Tp1>& __a, const polymorphic_allocator<_Tp2>& __b) noexcept -- cgit v1.1