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de637db263
Summary:
This patch is similar to the <list> fix but it has a few differences. This patch doesn't use a `__link_pointer` typedef because we don't need to change the linked list pointers because `forward_list` never stores a `__forward_begin_node` in the linked list itself.
The issue with `forward_list` is that the iterators store pointers to `__forward_list_node` and not `__forward_begin_node`. This is incorrect because `before_begin()` and `cbefore_begin()` return iterators that point to a `__forward_begin_node`. This means we incorrectly downcast the `__forward_begin_node` pointer to a `__node_pointer`. This downcast itself is sometimes UB but it cannot be safely removed until ABI v2. The more common cause of UB is when we deference the downcast pointer. (for example `__ptr_->__next_`). This can be fixed without an ABI break by upcasting `__ptr_` before accessing it.
The fix is as follows:
1. Introduce a `__iter_node_pointer` typedef that works similar to `__link_pointer` in the last patch. In ABI v2 it is always a typedef for `__begin_node_pointer`.
2. Change the `__before_begin()` method to return the correct pointer type (`__begin_node_pointer`),
Previously it incorrectly downcasted the `__forward_begin_node` to a `__node_pointer` so it could be used to constructor the iterator types.
3. Change `__forward_list_iterator` and `__forward_list_const_iterator` in the following way:
1. Change `__node_pointer __ptr_;` member to have the `__iter_node_pointer` type instead.
2. Add additional private constructors that accept `__begin_node_pointer` in addition to `__node_pointer` and then correctly cast them to the stored `__iter_node_pointer` type.
3. Add `__get_begin()` and `__get_node_unchecked()` accessor methods that correctly cast `__ptr_` to the expected pointer type. `__get_begin()` is always safe to use and should be
preferred. `__get_node_unchecked()` can only be used on a deferencible iterator.
4. Replace direct access to `__forward_list_iterator::__ptr_` with the safe accessor methods.
Reviewers: mclow.lists, EricWF
Subscribers: cfe-commits
Differential Revision: http://reviews.llvm.org/D15836
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@258888 91177308-0d34-0410-b5e6-96231b3b80d8
54 lines
1.1 KiB
C++
54 lines
1.1 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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// <forward_list>
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// forward_list()
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// forward_list::iterator()
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// forward_list::const_iterator()
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#include <forward_list>
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#include <cassert>
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#include "test_macros.h"
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#include "min_allocator.h"
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struct A {
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std::forward_list<A> d;
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std::forward_list<A>::iterator it;
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std::forward_list<A>::const_iterator it2;
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};
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#if TEST_STD_VER >= 11
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struct B {
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typedef std::forward_list<B, min_allocator<B>> FList;
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FList d;
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FList::iterator it;
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FList::const_iterator it2;
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};
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#endif
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int main()
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{
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{
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A a;
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assert(a.d.empty());
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a.it = a.d.begin();
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a.it2 = a.d.cbefore_begin();
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}
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#if TEST_STD_VER >= 11
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{
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B b;
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assert(b.d.empty());
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b.it = b.d.begin();
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b.it2 = b.d.cbefore_begin();
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}
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#endif
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}
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