Fix small_vector issues when assigning it to itself #15525
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lhecker
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Issue-Bug
lhecker
commented
Jun 7, 2023
Comment on lines
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| size_t _capacity; | ||
| size_t _size; |
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By not initializing these fields, the move constructor avoids writing to these members twice.
DHowett
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Jun 7, 2023
lhecker
commented
Jun 8, 2023
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| reserve(other._size); | ||
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| std::uninitialized_copy(other.begin(), other.end(), _uninitialized_begin()); | ||
| _size = other._size; |
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These 3 lines are now moved 1:1 into _copy_assign. This allows us to call _copy_assign without a prior clear in the constructor, because a newly constructed vector can't possibly have anything that needs to be cleared.
This makes the diff large, but actually barely anything changed.
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| if (other._capacity == N) | ||
| { | ||
| _data = &_buffer[0]; | ||
| _capacity = N; | ||
| _size = other._size; | ||
| // The earlier static_assert(std::is_nothrow_move_constructible_v<T>) | ||
| // ensures that we don't exit in a weird state with invalid `_size`. | ||
| #pragma warning(suppress : 26447) // The function is declared 'noexcept' but calls function '...' which may throw exceptions (f.6). | ||
| std::uninitialized_move(other.begin(), other.end(), _uninitialized_begin()); | ||
| std::destroy(other.begin(), other.end()); | ||
| } | ||
| else | ||
| { | ||
| _data = other._data; | ||
| _capacity = other._capacity; | ||
| _size = other._size; | ||
| _move_assign(other); | ||
| } | ||
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| other._data = &other._buffer[0]; | ||
| other._capacity = N; | ||
| other._size = 0; |
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These 21 lines are moved 1:1 into _move_assign, for the same reason as for _copy_assign.
carlos-zamora
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Jun 9, 2023
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Pretty straightforward. Thanks for writing some comments in the PR! Made it much easier to review!
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This commit achieves fixes the issue as described in the title by
checking whether the
thisandotherpointer are identical.As an added bonus it makes the copy and move constructors slightly
cheaper, as they don't try to destruct existing data anymore,
which doesn't exist anyways.
Validation Steps Performed