[OpenMP] Fix tasking + parallel bug

From the bug report, the runtime needs to initialize the nproc variables
(inside middle init) for each root when the task is encountered, otherwise,
a segfault can occur.

Bugzilla: https://bugs.llvm.org/show_bug.cgi?id=36720

Differential Revision: https://reviews.llvm.org/D49996


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@338313 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Jonathan Peyton

runtime/src/kmp_tasking.cpp

@@ -1025,6 +1025,9 @@ kmp_task_t *__kmp_task_alloc(ident_t *loc_ref, kmp_int32 gtid,
   kmp_taskdata_t *parent_task = thread->th.th_current_task;
   size_t shareds_offset;
 
+  if (!TCR_4(__kmp_init_middle))
+    __kmp_middle_initialize();
+
   KA_TRACE(10, ("__kmp_task_alloc(enter): T#%d loc=%p, flags=(0x%x) "
                 "sizeof_task=%ld sizeof_shared=%ld entry=%p\n",
                 gtid, loc_ref, *((kmp_int32 *)flags), sizeof_kmp_task_t,

runtime/test/tasking/bug_36720.c

@@ -0,0 +1,34 @@
+// RUN: %libomp-compile-and-run
+
+/*
+Bugzilla: https://bugs.llvm.org/show_bug.cgi?id=36720
+
+Assertion failure at kmp_runtime.cpp(1715): nthreads > 0.
+OMP: Error #13: Assertion failure at kmp_runtime.cpp(1715).
+
+The assertion fails even with OMP_NUM_THREADS=1. If the second task is removed,
+everything runs to completion. If the "omp parallel for" directives are removed
+from inside the tasks, once again everything runs fine.
+*/
+
+#define N 1024
+
+int main() {
+  #pragma omp task
+  {
+    #pragma omp parallel for
+    for (int i = 0; i < N; i++)
+      (void)0;
+  }
+
+  #pragma omp task
+  {
+    #pragma omp parallel for
+    for (int i = 0; i < N; ++i)
+      (void)0;
+  }
+
+  #pragma omp taskwait
+
+  return 0;
+}