[llvm] [openmp] [OpenMP][Runtime] Handling crash with `OMP_TARGET_OFFLOAD=DISABLED` and invoking `omp_get_default_device()` (PR #171789)

[via llvm-commits]

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+// RUN: %libomp-compile-and-run
+// REQUIRES: ompt
+//
+// Test that omp_get_default_device() returns the initial device (0) when
+// called from within a target region when OMP_TARGET_OFFLOAD=DISABLED.
+// The target region should execute on the host.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <omp.h>
+
+extern void kmp_set_defaults(char const *str);
+
+int main() {
+  // Set non-zero default device using API (more direct than env var)
+  omp_set_default_device(4);
+
+  // Now disable offload
+  kmp_set_defaults("OMP_TARGET_OFFLOAD=DISABLED");
+
+// Force parallel region to initialize runtime
+#pragma omp parallel
+  {
+  }
+
+  int initial_device = omp_get_initial_device();
+  int host_default_device = omp_get_default_device();
+  int target_default_device = -1;
+  int target_is_initial = -1;
+
+  printf("Host context:\n");
+  printf("  initial_device = %d\n", initial_device);
+  printf("  default_device = %d\n", host_default_device);
+
+// Call omp_get_default_device() from within target region
+// When offload is disabled, this should execute on host
+#pragma omp target map(from : target_default_device, target_is_initial)
+  {
+    target_default_device = omp_get_default_device();
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jprotze wrote:

> When called from within a target region the effect of this routine is unspecified.

https://github.com/llvm/llvm-project/pull/171789