nvc/nvfortran -mp=gpu: compile succeeds but the kernel is missing at run time ("Failed to find device function") for function pointers, static locals, VLAs, long double, type-bound calls

// # Draft finding: omp52-c-w-function-pointer on nvhpc
//
// - compiler: nvhpc
// - toolchain: nvhpc; arch: sm_80; machine: wingtip; memory mode: copy; opt: -O2
// - program: catalog omp52-c-w-function-pointer (c, version 52, sha256 b55bf877e3962528)
// - expected: check=pass (trusted; elision + model)
// - actual: run_error  (exit_status: 1; without mandatory: exit_status: 1) [the confirmer's class run_error; the matrix's class of the same run is wrong_answer: a run that fails]
// - observed: the run ends with "Accelerator Fatal Error: Failed to find device function 'nvkernel_main_F1L31_2'! File was compiled with: -gpu=cc80" (NVHPC 25.11 and 26.9, both memory modes): the compile succeeds without generating the target region's kernel; split: the static local, VLA and long double forms are findings of their own
// - verdict: compiler_bug by rule R20-runtime-bug: a legal program fails at run time, deterministically, against an expected value from two or more independent sources with an executed witness, and another toolchain, mode, arch or the elision gives the expected value
// - reason: expected trusted check=pass (elision + model): stored main verdict: elision + model agree; witnesses: afar/gfx942/copy, cce19/gfx942/copy, cce20/gfx942/copy, cce21/gfx942/copy, elision
// - citations: RUL-DERIVED-NEEDS-EXECUTION (rulings.md); RUL-WITNESS-PER-MODE (rulings.md); RUL-SAME-COMPILER-RUNS (rulings.md); RUL-PRESENCE-WITNESS (rulings.md); RUL-METAMORPHIC-OTHER-FAMILY (rulings.md)
// - legality: legal: offload.engine.prerun.check accepts it (rerun: offload.engine.rules with the
//   race rule and the restriction checks, and the AFAR clang front end, not under test here); no
//   compiler under test, gfortran or gcc is a legality witness
// - witnesses: afar/gfx942/copy, cce19/gfx942/copy, cce20/gfx942/copy, cce21/gfx942/copy, elision
// - withdrawn: none
//
// Generated by compliance.widen (OpenMP 5.2, C11; catalog widening). Do not edit.
// id: omp52-c-w-function-pointer
// primary atom: base.device.function_pointer
// atoms: base.device.function_pointer
// legal: yes
// observable: yes
// ran_on_host: inside the target region of interest
// evidence: construct
// needs: none
// std: c11
// feature: a pointer to a declare target function taken and called in device code
// spec: OpenMP 5.2 §13.8, p.287: a program may rely on a function address in a target region for assignments, comparisons to zero and indirect calls
#include <stdio.h>
#include <stdbool.h>
#include <omp.h>

enum { n = 64 };

#pragma omp declare target
int tw(int x) { return 2 * x + 1; }
int th(int x) { return 3 * x; }
#pragma omp end declare target

int main(void) {
  int a[n], b[n], ref[n];
  int host_flag = 1;
  for (int i = 0; i < n; i++) {
    a[i] = i + 1;
    b[i] = 0;
    ref[i] = (i % 2) ? 2 * (i + 1) + 1 : 3 * (i + 1);
  }
  #pragma omp target teams distribute parallel for map(to: a) map(from: b) map(tofrom: \
      host_flag)
  for (int i = 0; i < n; i++) {
    int (*f)(int) = (i % 2) ? tw : th;
    b[i] = f(a[i]);
    if (i == 0) host_flag = omp_is_initial_device();
  }
  bool ok = true;
  for (int i = 0; i < n; i++)
    ok = ok && (b[i] == ref[i]);
  printf("RESULT ran_on_host=%d check=%s\n", host_flag, ok ? "pass" : "fail");
  return 0;
}