[OpenMP] Use half of available logical processors for collapse tests (l…

…lvm#88319)

The new collapse test cases define `MAX_THREADS` to be 256 and use all
available threads/logical processors on the system. This triples the
testing time on an AIX machine that has 128 logical processors. This
patch changes to use half of available logical processors to avoid over
subscribing because there are other libomp tests running at the same
time, including 2 other such collapse tests.

openmp/runtime/test/worksharing/for/collapse_test.inc

@@ -18,9 +18,9 @@
 #define MAX_THREADS 256
 
 #if defined VERBOSE
-#define PRINTF printf
+#define PRINTF(...) printf(__VA_ARGS__)
 #else
-#define PRINTF
+#define PRINTF(...)
 #endif
 
 LOOP_TYPE0 iLB, iUB;
@@ -106,12 +106,21 @@ int test() {
   unsigned scalarCount = 0;
   unsigned uselessThreadsOpenMP = 0;
   unsigned usefulThreadsOpenMP = 0;
-  unsigned chunkSizesOpenmp[MAX_THREADS] = {0};
 
-  unsigned num_threads = omp_get_max_threads();
+  // Use half of the available threads/logical processors.
+  unsigned num_threads = omp_get_max_threads() / 2;
+
+  // Make sure num_threads is not 0 after the division in case
+  // omp_get_max_threads() returns 1.
+  if (num_threads == 0)
+    num_threads = 1;
+
   if (num_threads > MAX_THREADS)
     num_threads = MAX_THREADS;
-  omp_set_num_threads(num_threads);
+
+  unsigned long *chunkSizesOpenmp =
+      (unsigned long *)malloc(sizeof(unsigned long) * num_threads);
+  memset(chunkSizesOpenmp, 0, sizeof(unsigned long) * num_threads);
 
   // count iterations and allocate space
   LOOP { ++trueCount; }
@@ -129,10 +138,10 @@ int test() {
   // perform and record OpenMP iterations and thread use
 #pragma omp parallel num_threads(num_threads)
   {
+    unsigned gtid = omp_get_thread_num();
 #pragma omp for collapse(3) private(i, j, k)
     LOOP {
       unsigned count;
-      unsigned gtid = omp_get_thread_num();
 #pragma omp atomic update
       ++chunkSizesOpenmp[gtid];
 #pragma omp atomic capture
@@ -197,5 +206,6 @@ int test() {
   // clean up space
   FreeSpace(openmpSpace);
   FreeSpace(scalarSpace);
+  free(chunkSizesOpenmp);
   return pass;
 }