[llvm-bugs] [Bug 42061] New: Math function conflict when using clang++

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42061

            Bug ID: 42061
           Summary: Math function conflict when using clang++
           Product: OpenMP
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Clang Compiler Support
          Assignee: unassignedclangbugs at nondot.org
          Reporter: csdaley at lbl.gov
                CC: llvm-bugs at lists.llvm.org

I encounter a math function conflict issue when using clang++. The conflict
does not happen when using clang. I am using LLVM/Clang/OpenMP commits from
today, 29 May 2019. Please see below

csdaley at cgpu03:~/llvm> cat hello.c
#include <stdio.h>
#include <stdlib.h>

int main()
{
  printf("hello\n");
  return 0;
}

csdaley at cgpu03:~/llvm> clang -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda
hello.c -o hello && ./hello 
hello

csdaley at cgpu03:~/llvm> clang++ -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda
hello.c -o hello && ./hello 
clang-9: warning: treating 'c' input as 'c++' when in C++ mode, this behavior
is deprecated [-Wdeprecated]
In file included from hello.c:2:
In file included from /opt/gcc/7.3.0/snos/include/g++/stdlib.h:36:
In file included from /opt/gcc/7.3.0/snos/include/g++/cstdlib:77:
/opt/gcc/7.3.0/snos/include/g++/bits/std_abs.h:70:3: error: declaration
conflicts with target of using declaration already in scope
  abs(double __x)
  ^
/project/projectdirs/m1759/csdaley/software/cgpu/llvm/9.0.0-git_20190529/lib/clang/9.0.0/include/__clang_cuda_math_forward_declares.h:50:25:
note: target of using declaration
__DEVICE__ const double abs(const double);
                        ^
/opt/gcc/7.3.0/snos/include/g++/bits/std_abs.h:52:11: note: using declaration
  using ::abs;
          ^
/opt/gcc/7.3.0/snos/include/g++/bits/std_abs.h:74:3: error: declaration
conflicts with target of using declaration already in scope
  abs(float __x)
  ^
/project/projectdirs/m1759/csdaley/software/cgpu/llvm/9.0.0-git_20190529/lib/clang/9.0.0/include/__clang_cuda_math_forward_declares.h:51:24:
note: target of using declaration
__DEVICE__ const float abs(const float);
                       ^
/opt/gcc/7.3.0/snos/include/g++/bits/std_abs.h:52:11: note: using declaration
  using ::abs;
          ^
2 errors generated.

csdaley at cgpu03:~/llvm> clang++ -v
clang version 9.0.0 (https://github.com/llvm-mirror/clang
e420b2015caea78d84601f697fbc33b6116ec622) (https://github.com/llvm-mirror/llvm
36c062c0837bba4d6fc18b4132ab3df6a8cc4113)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir:
/project/projectdirs/m1759/csdaley/software/cgpu/llvm/9.0.0-git_20190529/bin
Found candidate GCC installation:
/opt/gcc/7.3.0/snos/lib/gcc/x86_64-suse-linux/7.3.0
Selected GCC installation: /opt/gcc/7.3.0/snos/lib/gcc/x86_64-suse-linux/7.3.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
Found CUDA installation: /global/common/cori/software/cuda/9.2, version 9.2



I have been in discussion with Doru and Johannes about this bug. They confirmed
that it is a bug and suggested putting the bug in bugzilla. The latest response
from Doru is

"The fix would be to remove the const float and const double variants of the
abs functions. This unfortunately will break the inclusion of the "random"
header.

I'm not sure how to reconcile those two errors, it looks like those two fixes
cannot coexist. Maybe I'm missing something."

Thanks,
Chris

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