Clang can't compile libstdc++ ranges

[llvmbot]

Bugzilla Link	46746
Version	trunk
OS	Linux
Attachments	Preprocessed example that reproduces the error.
Reporter	LLVM Bugzilla Contributor
CC	@avikivity,@JohelEGP,@mmatrosov,@zygoloid,@HighCommander4

Extended Description

GCC 10.1.0 came with libstdc++ that has <ranges> implemented. Also clang 10 supports concepts. I wanted to use clang to compile a simple snippet that relies on ranges, but clang encountered some errors that just don't happen with gcc.

#include <ranges>

int main(void)
{
 char c[3] = {'a', 'b', 'v'};
 std::ranges::subrange sub(c);
}

The preprocessed file can be found here: https://godbolt.org/z/7hfbq5
I've also made an attachment with the same preprocessed file compressed.

[llvmbot]

Hm, I've just realized that gcc also can't compile the code if clang is used to preprocess it first.

[HighCommander4]

Hm, I've just realized that gcc also can't compile the code if clang is used
to preprocess it first.

I think that's expected. Standard library headers contain preprocessor branches conditioned on things like __has_builtin(). Since gcc and clang don't support the exact same set of builtins, preprocessing with one can easily result in code that's not compilable with the other.

[avikivity]

Here's another example that fails with clang:

======= begin example =============
#include

void foo() {
std::ranges::iota_view iota(2, 10);
iota.begin();
}
======== end example ==============

clang complains that iota_view doesn't have a begin(), which it does.

[avikivity]

I think this is a libstdc++ bug. Details here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97120.

[mmatrosov]

Another example:

#include
#include
#include

std::map<int, int> map;

int main() {
map[0] = 10;
map[1] = 20;
for (int key : std::ranges::views::keys(map)) {
std::cout << key << ' ';
}
}

https://godbolt.org/z/4GbrG3a5W

[mmatrosov]

I blieve this is due to this bug: llvm/llvm-bugzilla-archive#50864

[0x8000-0000]

mentioned in issue llvm/llvm-bugzilla-archive#50328

[mmatrosov]

mentioned in issue llvm/llvm-bugzilla-archive#50864

[royjacobson]

Confirmed to work after https://reviews.llvm.org/D126907, so this was also a duplicate of #44178. Closing.

[llvmbot]

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