[OpenMP][libc++] including <iostream> when targeting amdgpu caues error: use of undeclared identifier '__not_found'

[tom91136]

There seems to be a header inclusion bug in

llvm-project/clang/lib/Headers/__clang_hip_math.h

Line 18 in a7517e1

#include <algorithm>

That header file doesn't seems to have an actual need for <algorithm> but its inclusion cases failures down the line.
For example:

#include <iostream>
int main() {
#pragma omp target
  {}
  return 0;
}

Compiling the program causes a header related error only when targeting amdgpu:

// clang++ -std=c++17 -stdlib=libc++ -fexperimental-library -fopenmp --offload-arch=gfx1036 mp_sample.cpp -O2 # -Xclang -ast-dump
// In file included from mp_sample.cpp:1:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/iostream:43:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/ios:222:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__locale:16:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__mutex/once_flag.h:21:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/tuple:268:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/compare:145:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/compare_partial_order_fallback.h:13:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/partial_order.h:14:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/weak_order.h:14:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/strong_order.h:20:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/lib/clang/18/include/openmp_wrappers/cmath:17:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/cmath:319:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/lib/clang/18/include/openmp_wrappers/math.h:55:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/lib/clang/18/include/__clang_hip_math.h:18:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/algorithm:1977:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/iterator:683:
// In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__iterator/common_iterator.h:31:
/// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:402:21: error: use of undeclared identifier '__not_found'
//  402 |   size_t __result = __not_found;
//      |                     ^
/// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:405:23: error: use of undeclared identifier '__not_found'
//  405 |       if (__result != __not_found) {
//      |                       ^
/// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:406:16: error: use of undeclared identifier '__ambiguous'
//  406 |         return __ambiguous;
//      |                ^
/// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:419:45: error: use of undeclared identifier '__not_found'
//  419 | struct __find_unambiguous_index_sfinae_impl<__not_found> {};
//      |                                             ^
/// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:422:45: error: use of undeclared identifier '__ambiguous'
//  422 | struct __find_unambiguous_index_sfinae_impl<__ambiguous> {};
//      |                                             ^
//  ... goes on...

Targeting nvptx works as expected.
Manually removing #include <algorithm> in __clang_hip_math.h works, and so does adding #include <algorithm> before #include <iostream> in the reproducer program.

The actual cause seems to be an ordering issue, as __not_found is defined in <tuple> but that header's include chain eventually leads to __iterator/common_iterator.h which depends on <variant> in OpenMP target's amdgpu case, and <variant> expects some of the symbols from <tuple> (which isn't defined just yet).

In case it matters:

> clang++
clang version 18.0.0 (git@github.com:tom91136/llvm-project.git 96adadf8f7227f6543537056f27f98cb18bbe8ce)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/tom/software/llvm-ompt/96adadf8f722/bin
Found candidate GCC installation: /usr/lib/gcc/i686-redhat-linux/12
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/12
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/12
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
Found HIP installation: /opt/rocm, version 5.5.30202

[jdoerfert]

@jhuber6 We should get rid of these headers ... for now, can you check out the proposed solutions?

[llvmbot]

@llvm/issue-subscribers-openmp

There seems to be a header inclusion bug in https://github.com/llvm/llvm-project/blob/a7517e12caab0750d3dfd7c0c6faec9acc7e5a2b/clang/lib/Headers/__clang_hip_math.h#L18 That header file doesn't seems to have an actual need for `<algorithm>` but its inclusion cases failures down the line. For example: ``` #include <iostream> int main() { #pragma omp target {} return 0; } ``` Compiling the program causes a header related error only when targeting amdgpu: ``` // clang++ -std=c++17 -stdlib=libc++ -fexperimental-library -fopenmp --offload-arch=gfx1036 mp_sample.cpp -O2 # -Xclang -ast-dump // In file included from mp_sample.cpp:1: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/iostream:43: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/ios:222: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__locale:16: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__mutex/once_flag.h:21: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/tuple:268: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/compare:145: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/compare_partial_order_fallback.h:13: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/partial_order.h:14: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/weak_order.h:14: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__compare/strong_order.h:20: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/lib/clang/18/include/openmp_wrappers/cmath:17: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/cmath:319: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/lib/clang/18/include/openmp_wrappers/math.h:55: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/lib/clang/18/include/__clang_hip_math.h:18: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/algorithm:1977: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/iterator:683: // In file included from /home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/__iterator/common_iterator.h:31: /// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:402:21: error: use of undeclared identifier '__not_found' // 402 | size_t __result = __not_found; // | ^ /// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:405:23: error: use of undeclared identifier '__not_found' // 405 | if (__result != __not_found) { // | ^ /// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:406:16: error: use of undeclared identifier '__ambiguous' // 406 | return __ambiguous; // | ^ /// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:419:45: error: use of undeclared identifier '__not_found' // 419 | struct __find_unambiguous_index_sfinae_impl<__not_found> {}; // | ^ /// home/tom/software/llvm-ompt/96adadf8f722/bin/../include/c++/v1/variant:422:45: error: use of undeclared identifier '__ambiguous' // 422 | struct __find_unambiguous_index_sfinae_impl<__ambiguous> {}; // | ^ // ... goes on... ``` Targeting nvptx works as expected. Manually removing `#include <algorithm>` in `__clang_hip_math.h` works, and so does adding `#include <algorithm>` before `#include <iostream>` in the reproducer program.

The actual cause seems to be an ordering issue, as __not_found is defined in <tuple> but that header's include chain eventually leads to __iterator/common_iterator.h which depends on <variant> in OpenMP target's amdgpu case, and <variant> expects some of the symbols from <tuple> (which isn't defined just yet).

In case it matters:

> clang++
clang version 18.0.0 (git@<!-- -->github.com:tom91136/llvm-project.git 96adadf8f7227f6543537056f27f98cb18bbe8ce)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/tom/software/llvm-ompt/96adadf8f722/bin
Found candidate GCC installation: /usr/lib/gcc/i686-redhat-linux/12
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/12
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/12
Candidate multilib: .;@<!-- -->m64
Candidate multilib: 32;@<!-- -->m32
Selected multilib: .;@<!-- -->m64
Found HIP installation: /opt/rocm, version 5.5.30202