[PATCH] D11269: Patch out an (apparently unwarranted) fatal assertion in OpenMP runtime until preconditions are met

[John Mellor-Crummey]

jmellorcrummey created this revision.
jmellorcrummey added reviewers: AndreyChurbanov, llvm-commits.
jmellorcrummey added subscribers: llvm-commits, openmp-commits.

Compiling the code below with g++ and linking it to the LLVM OpenMP runtime compiled in debug mode trips an assertion that produces a fatal error. When the assertion is skipped, the program runs successfully to completion and produces the same answer as the sequential code. Intel will restore the assertion with a patch that fixes the issues that cause it to trip.

The program:

#include <inttypes.h>
#include <stdio.h>
#include <omp.h>

#define NTHREADS 8
#define NBOUND 40 

uint64_t result[NBOUND]; 

uint64_t fib(int n) 
{
  if (n < 2) return n;
  else return fib(n-1) + fib(n-2);
}

void testparallel()
{
#pragma omp parallel num_threads(NTHREADS) 
  {
#pragma omp for
    for(int i = 0; i < NBOUND; i++)  result[i] = fib(40);
  }
}

void teststatic()
{
#pragma omp parallel for schedule(static)
  for(int i = 0; i < NBOUND; i++) result[i] += fib(40);
}

int main(int argc, char **argv)
{
  int i;

  testparallel();
  teststatic();

  for(i=0;i< NBOUND;i++) printf("%lld ", result[i]);
  printf("\n");
}

http://reviews.llvm.org/D11269

Files:
  runtime/src/kmp_runtime.c

Index: runtime/src/kmp_runtime.c
===================================================================
--- runtime/src/kmp_runtime.c
+++ runtime/src/kmp_runtime.c
@@ -2086,7 +2086,11 @@
 
     if ( __kmp_tasking_mode != tskm_immediate_exec ) {
         // Set master's task team to team's task team. Unless this is hot team, it should be NULL.
+#if 0
+        // Patch out an assertion that trips while the runtime seems to operate correctly.
+        // Avoiding the preconditions that cause the assertion to trip has been promised as a forthcoming patch.
         KMP_DEBUG_ASSERT(master_th->th.th_task_team == parent_team->t.t_task_team[master_th->th.th_task_state]);
+#endif
         KA_TRACE( 20, ( "__kmp_fork_call: Master T#%d pushing task_team %p / team %p, new task_team %p / team %p\n",
                       __kmp_gtid_from_thread( master_th ), master_th->th.th_task_team,
                       parent_team, team->t.t_task_team[master_th->th.th_task_state], team ) );


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