2ae4b92a1c
In #135303, we started using `__bit_log2` instead of `__log2i` inside `std::sort`. However, `__bit_log2` has a precondition that `__log2i` didn't have, which is that the input is non-zero. While it technically makes no sense to request the logarithm of 0, `__log2i` handled that case and returned 0 without issues. After switching to `__bit_log2`, passing 0 as an input results in an unsigned integer overflow which can trigger `-fsanitize=unsigned-integer-overflow`. While not technically UB in itself, it's clearly not intended either. To fix this, we add an internal assertion to `__bit_log2` which catches the issue in our test suite, and we make sure not to violate `__bit_log2`'s preconditions before we call it from `std::sort`.
51 lines
2.7 KiB
C++
51 lines
2.7 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include <algorithm>
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#include <bit>
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class Comp, class RandomAccessIterator>
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void __sort(RandomAccessIterator first, RandomAccessIterator last, Comp comp) {
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if (first == last) // log(0) is undefined, so don't try computing the depth
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return;
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auto depth_limit = 2 * std::__bit_log2(static_cast<size_t>(last - first));
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// Only use bitset partitioning for arithmetic types. We should also check
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// that the default comparator is in use so that we are sure that there are no
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// branches in the comparator.
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std::__introsort<_ClassicAlgPolicy,
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ranges::less,
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RandomAccessIterator,
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__use_branchless_sort<ranges::less, RandomAccessIterator>>(first, last, ranges::less{}, depth_limit);
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}
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// clang-format off
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template void __sort<__less<char>&, char*>(char*, char*, __less<char>&);
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#if _LIBCPP_HAS_WIDE_CHARACTERS
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template void __sort<__less<wchar_t>&, wchar_t*>(wchar_t*, wchar_t*, __less<wchar_t>&);
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#endif
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template void __sort<__less<signed char>&, signed char*>(signed char*, signed char*, __less<signed char>&);
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template void __sort<__less<unsigned char>&, unsigned char*>(unsigned char*, unsigned char*, __less<unsigned char>&);
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template void __sort<__less<short>&, short*>(short*, short*, __less<short>&);
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template void __sort<__less<unsigned short>&, unsigned short*>(unsigned short*, unsigned short*, __less<unsigned short>&);
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template void __sort<__less<int>&, int*>(int*, int*, __less<int>&);
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template void __sort<__less<unsigned>&, unsigned*>(unsigned*, unsigned*, __less<unsigned>&);
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template void __sort<__less<long>&, long*>(long*, long*, __less<long>&);
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template void __sort<__less<unsigned long>&, unsigned long*>(unsigned long*, unsigned long*, __less<unsigned long>&);
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template void __sort<__less<long long>&, long long*>(long long*, long long*, __less<long long>&);
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template void __sort<__less<unsigned long long>&, unsigned long long*>(unsigned long long*, unsigned long long*, __less<unsigned long long>&);
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template void __sort<__less<float>&, float*>(float*, float*, __less<float>&);
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template void __sort<__less<double>&, double*>(double*, double*, __less<double>&);
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template void __sort<__less<long double>&, long double*>(long double*, long double*, __less<long double>&);
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// clang-format on
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_LIBCPP_END_NAMESPACE_STD
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