[OpenMP][libomp] Fix omp_get_wtime.c test

[jlpeyton]

Summary

Drop trying to test "precise" wall clock time and just test that successive calls to omp_get_wtime() are monotonically increasing.

[jlpeyton]

https://reviews.llvm.org/D112458 addresses this instead.

openmp/runtime/test/api/omp_get_wtime.c

 // RUN: %libomp-compile-and-run
 #include <stdio.h>
 #include <stdlib.h>
 #include "omp_testsuite.h"
 #include "omp_my_sleep.h"
 
-#define NTIMES 100
-
-// This is the error % threshold. Be generous with the error threshold since
-// this test may be run in parallel with many other tests it may throw off the
-// sleep timing.
-#define THRESHOLD 100.0
-
-double test_omp_get_wtime(double desired_wait_time) {
-  double start;
-  double end;
-  start = 0;
-  end = 0;
+// Return 0 if success, 1 if failure
+//
+// Trying to test a precise elapsed wall clock time is impossible due to
+// non-deterministic workloads on the test machine and OS scheduling quirks
+// which may affect the timing of the test.
+//
+// Only test that a successive call to omp_get_wtime()
+// returns a larger (or equal) value than the previous call.
+int test_omp_get_wtime() {
+  double start, stop;
   start = omp_get_wtime();
-  my_sleep(desired_wait_time);
-  end = omp_get_wtime();
-  return end - start;
-}
-
-int compare_times(const void *lhs, const void *rhs) {
-  const double *a = (const double *)lhs;
-  const double *b = (const double *)rhs;
-  return *a - *b;
+  my_sleep(0.05);
+  stop = omp_get_wtime();
+  if (start > stop)
+    return 1;
+  return 0;
 }
 
 int main() {
-  int i, final_count;
-  double percent_off;
-  double *begin, *end, *ptr;
-  double wait_time = 0.01;
-  double average = 0.0;
-  double n = 0.0;
-  double *times = (double *)malloc(sizeof(double) * NTIMES);
-
-  // Get each timing
-  for (i = 0; i < NTIMES; i++) {
-    times[i] = test_omp_get_wtime(wait_time);
-  }
-
-  // Remove approx the "worst" tenth of the timings
-  qsort(times, NTIMES, sizeof(double), compare_times);
-  begin = times;
-  end = times + NTIMES;
-  for (i = 0; i < NTIMES / 10; ++i) {
-    if (i % 2 == 0)
-      begin++;
-    else
-      end--;
-  }
-
-  // Get the average of the remaining timings
-  for (ptr = begin, final_count = 0; ptr != end; ++ptr, ++final_count)
-    average += times[i];
-  average /= (double)final_count;
-  free(times);
-
-  // Calculate the percent off of desired wait time
-  percent_off = (average - wait_time) / wait_time * 100.0;
-  // Should always be positive, but just in case
-  if (percent_off < 0)
-    percent_off = -percent_off;
-
-  if (percent_off > (double)THRESHOLD) {
-    fprintf(stderr, "error: average of %d runs (%lf) is of by %lf%%\n", NTIMES,
-            average, percent_off);
+  int i, errs = 0;
+  for (i = 0; i < REPETITIONS; ++i)
+    errs += test_omp_get_wtime();
+  if (errs)
     return EXIT_FAILURE;
-  }
-  printf("pass: average of %d runs (%lf) is only off by %lf%%\n", NTIMES,
-         average, percent_off);
   return EXIT_SUCCESS;
 }