* [PATCH] Simplify allocator usage in unordered containers
@ 2017-08-18 20:04 Jonathan Wakely
0 siblings, 0 replies; only message in thread
From: Jonathan Wakely @ 2017-08-18 20:04 UTC (permalink / raw)
To: libstdc++, gcc-patches
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While fixing PR 81891 I noticed that _Hashtable always creates a
__value_alloc_type for constructing and destroying the elements, which
is unnecessary. https://wg21.link/lwg2218 confirmed that.
We can avoid constructing new allocators just for these calls and can
call them directly on the stored allocator.
* include/bits/hashtable_policy.h (_ReuseOrAllocNode): Remove
__value_alloc_type and __value_alloc_traits typedefs.
(_ReuseOrAllocNode::operator()): Call construct and destroy on the
node allocator.
(_Hashtable_alloc): Simplify __value_alloc_traits typedef.
(_Hashtable_alloc<_NodeAlloc>::_M_allocate_node(_Args&&...)): Call
construct on the node allocator.
(_Hashtable_alloc<_NodeAlloc>::_M_deallocate_node(__node_type*)): Call
destroy on the node allocator.
Tested powerpc64le-linux, committed to trunk.
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commit caa7283396a9f74a42c979697beeee0a53115cee
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Aug 18 19:12:00 2017 +0100
Simplify allocator usage in unordered containers
* include/bits/hashtable_policy.h (_ReuseOrAllocNode): Remove
__value_alloc_type and __value_alloc_traits typedefs.
(_ReuseOrAllocNode::operator()): Call construct and destroy on the
node allocator.
(_Hashtable_alloc): Simplify __value_alloc_traits typedef.
(_Hashtable_alloc<_NodeAlloc>::_M_allocate_node(_Args&&...)): Call
construct on the node allocator.
(_Hashtable_alloc<_NodeAlloc>::_M_deallocate_node(__node_type*)): Call
destroy on the node allocator.
diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index a3a31d1fb11..5f2d8776aaa 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -111,9 +111,6 @@ namespace __detail
private:
using __node_alloc_type = _NodeAlloc;
using __hashtable_alloc = _Hashtable_alloc<__node_alloc_type>;
- using __value_alloc_type = typename __hashtable_alloc::__value_alloc_type;
- using __value_alloc_traits =
- typename __hashtable_alloc::__value_alloc_traits;
using __node_alloc_traits =
typename __hashtable_alloc::__node_alloc_traits;
using __node_type = typename __hashtable_alloc::__node_type;
@@ -135,18 +132,17 @@ namespace __detail
__node_type* __node = _M_nodes;
_M_nodes = _M_nodes->_M_next();
__node->_M_nxt = nullptr;
- __value_alloc_type __a(_M_h._M_node_allocator());
- __value_alloc_traits::destroy(__a, __node->_M_valptr());
+ auto& __a = _M_h._M_node_allocator();
+ __node_alloc_traits::destroy(__a, __node->_M_valptr());
__try
{
- __value_alloc_traits::construct(__a, __node->_M_valptr(),
- std::forward<_Arg>(__arg));
+ __node_alloc_traits::construct(__a, __node->_M_valptr(),
+ std::forward<_Arg>(__arg));
}
__catch(...)
{
__node->~__node_type();
- __node_alloc_traits::deallocate(_M_h._M_node_allocator(),
- __node, 1);
+ __node_alloc_traits::deallocate(__a, __node, 1);
__throw_exception_again;
}
return __node;
@@ -2000,10 +1996,8 @@ namespace __detail
// Use __gnu_cxx to benefit from _S_always_equal and al.
using __node_alloc_traits = __gnu_cxx::__alloc_traits<__node_alloc_type>;
- using __value_type = typename __node_type::value_type;
- using __value_alloc_type =
- __alloc_rebind<__node_alloc_type, __value_type>;
- using __value_alloc_traits = std::allocator_traits<__value_alloc_type>;
+ using __value_alloc_traits = typename __node_alloc_traits::template
+ rebind_traits<typename __node_type::value_type>;
using __node_base = __detail::_Hash_node_base;
using __bucket_type = __node_base*;
@@ -2057,10 +2051,10 @@ namespace __detail
__node_type* __n = std::__addressof(*__nptr);
__try
{
- __value_alloc_type __a(_M_node_allocator());
::new ((void*)__n) __node_type;
- __value_alloc_traits::construct(__a, __n->_M_valptr(),
- std::forward<_Args>(__args)...);
+ __node_alloc_traits::construct(_M_node_allocator(),
+ __n->_M_valptr(),
+ std::forward<_Args>(__args)...);
return __n;
}
__catch(...)
@@ -2076,8 +2070,7 @@ namespace __detail
{
typedef typename __node_alloc_traits::pointer _Ptr;
auto __ptr = std::pointer_traits<_Ptr>::pointer_to(*__n);
- __value_alloc_type __a(_M_node_allocator());
- __value_alloc_traits::destroy(__a, __n->_M_valptr());
+ __node_alloc_traits::destroy(_M_node_allocator(), __n->_M_valptr());
__n->~__node_type();
__node_alloc_traits::deallocate(_M_node_allocator(), __ptr, 1);
}
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