[libcxx-commits] [PATCH] D128146: [libc++] Use uninitialized algorithms for vector

[Evgeny Eltsin via Phabricator via libcxx-commits]

eaeltsin added a comment.

In D128146#3672212 <https://reviews.llvm.org/D128146#3672212>, @philnik wrote:

> In D128146#3672050 <https://reviews.llvm.org/D128146#3672050>, @bgraur wrote:
>
>> Hi folks,
>>
>> We have some code which compiles fine with the version previous to this patch and fails after.
>> The code compiles fine with godbolt: https://gcc.godbolt.org/z/ToPGG5cMb
>>
>> But fails when built with `clang` containing this revision.
>> Repro compilation command:
>>
>>   clang -stdlib=libc++ -std=gnu++17 \
>>     -c /tmp/test.cc \
>>     -o /tmp/test.o
>>
>> Compiler output:
>>
>>   /tmp/test.cc:5:17: error: assigning to 'float' from incompatible type 'Vx<float, 2>'
>>     data[Index] = std::forward<LastArg>(last_arg);
>>                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>   /tmp/test.cc:22:5: note: in instantiation of function template specialization 'SetData<0, 2, float, Vx<float, 2> &>' requested here
>>       SetData<0, Length, Element>(data_, std::forward<Args>(args)...);
>>       ^
>>   [redacted]/include/c++/v1/__memory/allocator.h:165:28: note: in instantiation of function template specialization 'Vx<float, 2>::Vx<Vx<float, 2> &>' requested here
>>           ::new ((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
>>                              ^
>>   [redacted]/include/c++/v1/__memory/allocator_traits.h:290:13: note: in instantiation of function template specialization 'std::allocator<Vx<float, 2>>::construct<Vx<float, 2>, Vx<float, 2> &>' requested here
>>           __a.construct(__p, _VSTD::forward<_Args>(__args)...);
>>               ^
>>   [redacted]/include/c++/v1/__memory/uninitialized_algorithms.h:536:31: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<Vx<float, 2>>>::construct<Vx<float, 2>, Vx<float, 2> &, void>' requested here
>>       allocator_traits<_Alloc>::construct(__alloc, std::__to_address(__first2), *__first1);
>>                                 ^
>>   [redacted]/include/c++/v1/vector:1012:22: note: in instantiation of function template specialization 'std::__uninitialized_allocator_copy<std::allocator<Vx<float, 2>>, Vx<float, 2> *, Vx<float, 2> *, Vx<float, 2> *>' requested here
>>     __tx.__pos_ = std::__uninitialized_allocator_copy(__alloc(), __first, __last, __tx.__pos_);
>>                        ^
>>   [redacted]/include/c++/v1/vector:1162:9: note: in instantiation of function template specialization 'std::vector<Vx<float, 2>>::__construct_at_end<Vx<float, 2> *>' requested here
>>           __construct_at_end(__x.__begin_, __x.__end_, __n);
>>           ^
>>   /tmp/test.cc:35:16: note: in instantiation of member function 'std::vector<Vx<float, 2>>::vector' requested here
>>     do_something(vertices);
>>                  ^
>>   1 error generated.
>
> I think this is a bug in your code. https://godbolt.org/z/sv8YehKhY fails the same way, but without `std::vector`. BTW the simplest fix would be to add `Vx(Vx& v) : Vx(std::as_const(v)) {}`.

@philnik , can you please help me understand what is going on with the original example posted by @bgraur ?

The fact is that the example compiled before this patch and failed with this patch. Even if the example is buggy, I still need to understand what the semantics were when it worked. Was it using the wrong ctor? Why did it change with this patch?

I'm seeing a number of tests failing with this patch, so understanding the example might give me a clue where to look.


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https://reviews.llvm.org/D128146