[OpenMP] Ignore teams ICV setters in restricted contexts (#194428)

This patch prevents `omp_set_num_teams()` and
`omp_set_teams_thread_limit()` from updating teams-related ICVs when
called from restricted runtime contexts.

The non-implicit parallel-region case follows the OpenMP 5.1
restriction. The active `teams`-region case is handled defensively
because these ICVs are device-scoped and updating them during an active
`teams` region can affect later teams execution.

The calls now warn and return without updating the ICVs. 

Fixes #194426.

openmp/runtime/src/i18n/en_US.txt

@@ -482,6 +482,8 @@ AffHWSubsetIgnoringAttr      "KMP_HW_SUBSET: ignoring %1$s attribute. This machi
 TargetMemNotAvailable        "Target memory not available, will use default allocator."
 AffIgnoringNonHybrid         "%1$s ignored: This machine is not a hybrid architecutre. Using \"%2$s\" instead."
 AffIgnoringNotAvailable      "%1$s ignored: %2$s is not available. Using \"%3$s\" instead."
+SetNumTeamsInParOrTeamsRegion "%1$s() called inside a parallel or teams region; call ignored."
+SetTeamsThreadLimitInParOrTeamsRegion "%1$s() called inside a parallel or teams region; call ignored."
 
 # --------------------------------------------------------------------------------------------------
 -*- HINTS -*-

openmp/runtime/src/kmp_ftn_entry.h

@@ -1636,9 +1636,23 @@ void FTN_STDCALL FTN_SET_NUM_TEAMS(int KMP_DEREF num_teams) {
   if (!__kmp_init_serial) {
     __kmp_serial_initialize();
   }
+  kmp_info_t *th = __kmp_entry_thread();
+  // OpenMP 5.1, Section 3.4.3: omp_set_num_teams may not be called from
+  // within a parallel region other than the implicit parallel region.
+  // Also guard against calls from within a teams region: nteams-var is a
+  // device-scoped ICV and concurrent modification from multiple team initial
+  // threads may race.
+  // t_level counts both active and serialized parallel levels (0 at the
+  // implicit top-level parallel region), so this catches all non-implicit
+  // parallel regions.
+  if (th->th.th_teams_microtask || th->th.th_team->t.t_level > 0) {
+    KMP_WARNING(SetNumTeamsInParOrTeamsRegion, "omp_set_num_teams");
+    return;
+  }
   __kmp_set_num_teams(KMP_DEREF num_teams);
 #endif
 }
+
 int FTN_STDCALL FTN_GET_MAX_TEAMS(void) {
 #ifdef KMP_STUB
   return 1;
@@ -1657,9 +1671,24 @@ void FTN_STDCALL FTN_SET_TEAMS_THREAD_LIMIT(int KMP_DEREF limit) {
   if (!__kmp_init_serial) {
     __kmp_serial_initialize();
   }
+  kmp_info_t *th = __kmp_entry_thread();
+  // OpenMP 5.1, Section 3.4.5: omp_set_teams_thread_limit may not be called
+  // from within a parallel region other than the implicit parallel region.
+  // Also guard against calls from within a teams region:
+  // teams-thread-limit-var is a device-scoped ICV and concurrent modification
+  // from multiple team initial threads may race.
+  // t_level counts both active and serialized parallel levels (0 at the
+  // implicit top-level parallel region), so this catches all non-implicit
+  // parallel regions.
+  if (th->th.th_teams_microtask || th->th.th_team->t.t_level > 0) {
+    KMP_WARNING(SetTeamsThreadLimitInParOrTeamsRegion,
+                "omp_set_teams_thread_limit");
+    return;
+  }
   __kmp_set_teams_thread_limit(KMP_DEREF limit);
 #endif
 }
+
 int FTN_STDCALL FTN_GET_TEAMS_THREAD_LIMIT(void) {
 #ifdef KMP_STUB
   return 1;

openmp/runtime/test/api/omp_nteams_api_restriction.c

@@ -0,0 +1,71 @@
+// RUN: %libomp-compile-and-run 2>&1 | FileCheck %s
+// Verify that omp_set_num_teams() and omp_set_teams_thread_limit() are
+// ignored when called from within a parallel or teams region.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <omp.h>
+
+int main(int argc, char **argv) {
+  int err = 0;
+
+  // Set initial values outside any region.
+  omp_set_num_teams(5);
+  omp_set_teams_thread_limit(7);
+
+  if (omp_get_max_teams() != 5) {
+    fprintf(stderr, "error: nteams-var not set correctly\n");
+    exit(1);
+  }
+  if (omp_get_teams_thread_limit() != 7) {
+    fprintf(stderr, "error: teams-thread-limit-var not set correctly\n");
+    exit(1);
+  }
+
+  // Call from inside a teams region -- should be ignored.
+  // Use num_teams(1) to ensure exactly one team and deterministic warning
+  // count.
+#pragma omp teams num_teams(1)
+  {
+    omp_set_num_teams(99);
+    omp_set_teams_thread_limit(99);
+  }
+
+  if (omp_get_max_teams() != 5) {
+    fprintf(stderr, "error: nteams-var modified inside teams region\n");
+    err++;
+  }
+  if (omp_get_teams_thread_limit() != 7) {
+    fprintf(stderr, "error: teams-thread-limit-var modified inside teams "
+                    "region\n");
+    err++;
+  }
+
+  // Call from inside a parallel region -- should be ignored.
+#pragma omp parallel num_threads(1)
+  {
+    omp_set_num_teams(99);
+    omp_set_teams_thread_limit(99);
+  }
+
+  if (omp_get_max_teams() != 5) {
+    fprintf(stderr, "error: nteams-var modified inside parallel region\n");
+    err++;
+  }
+  if (omp_get_teams_thread_limit() != 7) {
+    fprintf(stderr, "error: teams-thread-limit-var modified inside parallel "
+                    "region\n");
+    err++;
+  }
+
+  if (err == 0) {
+    printf("passed\n");
+  }
+  return err;
+}
+
+// CHECK: OMP: Warning{{.*}}omp_set_num_teams{{.*}}call ignored
+// CHECK: OMP: Warning{{.*}}omp_set_teams_thread_limit{{.*}}call ignored
+// CHECK: OMP: Warning{{.*}}omp_set_num_teams{{.*}}call ignored
+// CHECK: OMP: Warning{{.*}}omp_set_teams_thread_limit{{.*}}call ignored
+// CHECK: passed