Quuxplusone updated this revision to Diff 156210.
Quuxplusone edited the summary of this revision.
Quuxplusone added a comment.
Remove some incorrect `noexcept` from `<experimental/memory_resource>`.
I noticed this because the calls to `__clang_call_terminate` showed up on
Godbolt. But the pessimization is still there even without these `noexcept`!
Basically the flow is this:
std::pmr::vector::~vector (noexcept(true))
- polymorphic_allocator::destroy (noexcept(X) but inlineable)
- ~T (noexcept(true))
- polymorphic_allocator::deallocate (noexcept(X) but inlineable)
- memory_resource::deallocate (noexcept(false) and not inlineable)
where "X" is "true" before this patch and "false" afterward.
Even for `monotonic_buffer_resource`, we can't conclude that deallocation will
never throw, because deallocation *might* involve the upstream resource, which
we don't know anything about.
Repository:
rCXX libc++
https://reviews.llvm.org/D47344
Files:
include/experimental/memory_resource
src/experimental/memory_resource.cpp
Index: src/experimental/memory_resource.cpp
===================================================================
--- src/experimental/memory_resource.cpp
+++ src/experimental/memory_resource.cpp
@@ -8,6 +8,7 @@
//===----------------------------------------------------------------------===//
#include "experimental/memory_resource"
+#include "memory"
#ifndef _LIBCPP_HAS_NO_ATOMIC_HEADER
#include "atomic"
@@ -23,38 +24,47 @@
// new_delete_resource()
+#ifdef _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
+static bool is_aligned_to(void *ptr, size_t align)
+{
+ void *p2 = ptr;
+ size_t space = 1;
+ void *result = _VSTD::align(align, 1, p2, space);
+ return (result == ptr);
+}
+#endif
+
class _LIBCPP_TYPE_VIS __new_delete_memory_resource_imp
: public memory_resource
{
-public:
- ~__new_delete_memory_resource_imp() = default;
-
-protected:
- virtual void* do_allocate(size_t __size, size_t __align)
- { return _VSTD::__libcpp_allocate(__size, __align); /* FIXME */}
+ void *do_allocate(size_t bytes, size_t align) override
+ {
+ void *result = _VSTD::__libcpp_allocate(bytes, align);
+#ifdef _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
+ if (!is_aligned_to(result, align)) {
+ _VSTD::__libcpp_deallocate(result, align);
+ __throw_bad_alloc();
+ }
+#endif
+ return result;
+ }
- virtual void do_deallocate(void * __p, size_t, size_t __align)
- { _VSTD::__libcpp_deallocate(__p, __align); /* FIXME */ }
+ void do_deallocate(void *p, size_t, size_t align) override
+ { _VSTD::__libcpp_deallocate(p, align); }
- virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
- { return &__other == this; }
+ bool do_is_equal(const memory_resource& other) const _NOEXCEPT override
+ { return &other == this; }
};
// null_memory_resource()
class _LIBCPP_TYPE_VIS __null_memory_resource_imp
: public memory_resource
{
-public:
- ~__null_memory_resource_imp() = default;
-
-protected:
- virtual void* do_allocate(size_t, size_t) {
- __throw_bad_alloc();
- }
- virtual void do_deallocate(void *, size_t, size_t) {}
- virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT
- { return &__other == this; }
+ void *do_allocate(size_t, size_t) override { __throw_bad_alloc(); }
+ void do_deallocate(void *, size_t, size_t) override {}
+ bool do_is_equal(const memory_resource& other) const _NOEXCEPT override
+ { return &other == this; }
};
namespace {
Index: include/experimental/memory_resource
===================================================================
--- include/experimental/memory_resource
+++ include/experimental/memory_resource
@@ -195,7 +195,7 @@
}
_LIBCPP_INLINE_VISIBILITY
- void deallocate(_ValueType * __p, size_t __n) _NOEXCEPT {
+ void deallocate(_ValueType * __p, size_t __n) {
_LIBCPP_ASSERT(__n <= __max_size(),
"deallocate called for size which exceeds max_size()");
__res_->deallocate(__p, __n * sizeof(_ValueType), alignof(_ValueType));
@@ -265,7 +265,7 @@
template <class _Tp>
_LIBCPP_INLINE_VISIBILITY
- void destroy(_Tp * __p) _NOEXCEPT
+ void destroy(_Tp * __p)
{ __p->~_Tp(); }
_LIBCPP_INLINE_VISIBILITY
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