[Bug middle-end/105082] New: [OpenMP] [RFC] Add warning like LLVM's "declaration marked as declare target after first use, it may lead to incorrect results [-Wopenmp-target]" ?

[Bug middle-end/105082] New: [OpenMP] [RFC] Add warning like LLVM's "declaration marked as declare target after first use, it may lead to incorrect results [-Wopenmp-target]" ?

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105082

            Bug ID: 105082
           Summary: [OpenMP] [RFC] Add warning like LLVM's "declaration
                    marked as declare target after first use, it may lead
                    to incorrect results [-Wopenmp-target]" ?
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: diagnostic, openmp
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
  Target Milestone: ---

According to https://github.com/SOLLVE/sollve_vv/issues/506 , LLVM has the
following '-Wopenmp-target' warning.

RFC: Add a similar warning to warn_omp_declare_target_after_first_use ?
(
https://github.com/llvm/llvm-project/commit/729e242a7972f4802f982a4b4dabb964aa299675
)


warning: declaration marked as declare target after first use, it may lead to
incorrect results [-Wopenmp-target]
#pragma omp declare target link(a,b,c,i)


for code like:


int a[N], b[N], c[N];
int i = 0;

void update() {
  for (i = 0; i < N; i++) {
    a[i] += 1;
    b[i] += 2;
    c[i] += 3;
  }
}

#pragma omp declare target 
#pragma omp declare target link(a,b,c,i)  
#pragma omp declare target to(update)  
#pragma omp end declare target