ldionne requested changes to this revision. ldionne added a comment. This revision now requires changes to proceed. Herald added a subscriber: jkorous.
I believe this patch fixes an important QOI bug: see http://llvm.org/PR37574. I wholeheartedly agree with Eric that allocators-over-const are an abomination, however pointers-to-const are a fine thing and our implementation should handle them gracefully. Please rebase on top of `master` -- there's another function that does not appear in this diff that should be fixed too (`__construct_forward`). ================ Comment at: libcxx/include/memory:1645 - template <class _Tp> + template <class _SourceTp, class _DestTp> _LIBCPP_INLINE_VISIBILITY ---------------- Coming at it from a slightly different angle, I would think this is what we want: ``` template <class _SourceTp, class _DestTp, class _RawSourceTp = typename remove_const<_SourceTp>::type, class _RawDestTp = typename remove_const<_DestTp>::type> _LIBCPP_INLINE_VISIBILITY static typename enable_if< // We can use memcpy instead of a loop with construct if... is_trivially_move_constructible<_DestTp>::value && // - the Dest is trivially move constructible, and is_same<_RawSourceTp, _RawDestTp>::value && // - both types are the same modulo constness, and either (__is_default_allocator<allocator_type>::value || // + the allocator is the default allocator (and we know `construct` is just placement-new), or !__has_construct<allocator_type, _DestTp*, _SourceTp const&>::value), // + the allocator does not provide a custom `construct` method (so we'd fall back to placement-new) void>::type __construct_range_forward(allocator_type&, _SourceTp* __begin1, _SourceTp* __end1, _DestTp*& __begin2) { ptrdiff_t _Np = __end1 - __begin1; if (_Np > 0) { _VSTD::memcpy(const_cast<_RawDestTp*>(__begin2), __begin1, _Np * sizeof(_DestTp)); __begin2 += _Np; } } ``` And then we should have ``` template <class _Tp> struct __is_default_allocator : false_type { }; template <class _Tp> struct __is_default_allocator<_VSTD::allocator<_Tp> > : true_type { }; ``` Does this make sense? Also, I'm not sure I understand why we use `const_cast` on the destination type. It seems like we should instead enforce that it is non-const? But this is a pre-existing thing in the code, this doesn't affect this review. ================ Comment at: libcxx/include/memory:1690 < (is_same<allocator_type, allocator<_Tp> >::value || !__has_construct<allocator_type, _Tp*, _Tp>::value) && ---------------- This should be fixed in a similar way. ================ Comment at: libcxx/test/std/containers/sequences/vector/vector.cons/construct_iter_iter.pass.cpp:186 + std::vector<float> v(array, array + 3); + assert(std::fabs(v[0] - 0.0f) < FLT_EPSILON); + assert(std::fabs(v[1] - 1.0f) < FLT_EPSILON); ---------------- I do not understand this test, can you please explain? CHANGES SINCE LAST ACTION https://reviews.llvm.org/D48342/new/ https://reviews.llvm.org/D48342 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits