[Bug libgomp/122077] New: inscan reduction modifier does not compile on nvptx target with gcc 15.2

[schulz.benjamin at googlemail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122077

            Bug ID: 122077
           Summary: inscan reduction modifier does not compile on nvptx
                    target with gcc 15.2
           Product: gcc
           Version: 15.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: schulz.benjamin at googlemail dot com
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

openmp inscan reduction modifier does not compile on nvptx target with gcc 15.2



According to the openmp standard, the #pragma omp target parallel clause
supports the following clauses:

https://www.openmp.org/spec-html/5.0/openmpsu78.html

#pragma omp target parallel [clause[ [,] clause] ... ] new-line 


where clause can be any! of the clauses accepted by the target or! parallel
directives

The parallel directive supports the following clauses:

https://www.openmp.org/spec-html/5.0/openmpse14.html

reduction([reduction-modifier ,] reduction-identifier : list) 

reduction-modifier can be

https://www.openmp.org/spec-html/5.0/openmpsu107.html#x140-5810002.19.5.1

inscan 
task 
default


So lets make a test


#include <omp.h>

int main()
{
    int N=20;
   int a[N], b[N];
   int x = 0;

   // initialization
   for (int k = 0; k < N; k++)
      a[k] = k + 1;

   // a[k] is included in the computation of producing results in b[k]
   #pragma omp target data map(tofrom:a[0:N],b[0:N])
   #pragma omp target parallel for reduction(inscan,+: x)
   for (int k = 0; k < N; k++) {
      x += a[k];
      #pragma omp scan inclusive(x)
      b[k] = x;
   }


    return 0;
}

and compile with 
  -fopenmp -foffload=nvptx-none  -fcf-protection=none -fno-stack-protector



Error: »inscan«-»reduction«-clause with constructions except »for«, »simd«,
»for simd«, »parallel for«, »parallel for simd«
   15 |    #pragma omp target  parallel for reduction(inscan,+: x)
      |                                                         ^

Error: »#pragma omp scan« is only allowed to be used together with a loop
construct with an inscan reduction
   18 |       #pragma omp scan inclusive(x)
      |               ^~~


the reduction modifier task would work as reduction clause by the way.