[llvm-bugs] [Bug 48387] New: Signed loop variables get implicitly casted to unsigned (clang version >=11)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48387

            Bug ID: 48387
           Summary: Signed loop variables get implicitly casted to
                    unsigned (clang version >=11)
           Product: OpenMP
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: release blocker
          Priority: P
         Component: Clang Compiler Support
          Assignee: unassignedclangbugs at nondot.org
          Reporter: christoph.schwarzmeier at fau.de
                CC: llvm-bugs at lists.llvm.org

Compiling the following code snippet with `clang++ -fopenmp -Wsign-conversion`
generates warnings about the implicit conversion of the loop variables'
signedness:
warning: implicit conversion changes signedness: 'int' to 'unsigned int'
[-Wsign-conversion]

However, according to the OpenMP 5.0 standard, a loop variable can be "a
variable of a signed or unsigned integer type" [1], such that there should be
no type conversion required in the provided example.

This issue was initially observed with clang 11.0 on Ubuntu 18.04, but can also
be reproduced with the current clang x86-64 trunk version (tested on
"goodbolt.org").


#include <iostream>

int main() {
   int min = -10;
   int max = 10;

   #pragma omp parallel for
   for (int i = min; i <= max; ++i) {
      std::cout << i << std::endl;
   }

   return 0;
}


[1] https://www.openmp.org/spec-html/5.0/openmpsu40.html#x63-1260002.9.1

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