DRB006-indirectaccess2-orig-yes.c

/*
Copyright (c) 2017, Lawrence Livermore National Security, LLC.
Produced at the Lawrence Livermore National Laboratory
Written by Chunhua Liao, Pei-Hung Lin, Joshua Asplund,
Markus Schordan, and Ian Karlin
(email: liao6@llnl.gov, lin32@llnl.gov, asplund1@llnl.gov,
schordan1@llnl.gov, karlin1@llnl.gov)
LLNL-CODE-732144
All rights reserved.

This file is part of DataRaceBench. For details, see
https://github.com/LLNL/dataracebench. Please also see the LICENSE file
for our additional BSD notice.

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*/
/*
Two pointers have a distance of 12 (p1 - p2 = 12).
They are used as base addresses for indirect array accesses using an index set (another array).

The index set has two indices with a distance of 12 :
indexSet[5]- indexSet[0] = 533 - 521 =  12
So there is loop carried dependence (e.g. between loops with index values of 0 and 5).

We use the default loop scheduling (static even) in OpenMP.
It is possible that two dependent iterations will be scheduled
within a same chunk to a same thread. So there is no runtime data races.

When N is 180, two iteraions with N=0 and N= 5 have loop carried dependences.
For static even scheduling, we must have at least 36 threads (180/36=5 iterations)
so iteration 0 and 5 will be scheduled to two different threads.
Data race pair: xa1[idx]@128:5 vs. xa2[idx]@129:5
*/
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>

#define N 180
int indexSet[N] = {
521, 523, 525, 527, 529, 533, // 521+12=533
547, 549, 551, 553, 555, 557,
573, 575, 577, 579, 581, 583,
599, 601, 603, 605, 607, 609,
625, 627, 629, 631, 633, 635,

651, 653, 655, 657, 659, 661,
859, 861, 863, 865, 867, 869,
885, 887, 889, 891, 893, 895,
911, 913, 915, 917, 919, 921, 
937, 939, 941, 943, 945, 947,

963, 965, 967, 969, 971, 973,
989, 991, 993, 995, 997, 999, 
1197, 1199, 1201, 1203, 1205, 1207,
1223, 1225, 1227, 1229, 1231, 1233,
1249, 1251, 1253, 1255, 1257, 1259,

1275, 1277, 1279, 1281, 1283, 1285,
1301, 1303, 1305, 1307, 1309, 1311,
1327, 1329, 1331, 1333, 1335, 1337,
1535, 1537, 1539, 1541, 1543, 1545,
1561, 1563, 1565, 1567, 1569, 1571,

1587, 1589, 1591, 1593, 1595, 1597,
1613, 1615, 1617, 1619, 1621, 1623,
1639, 1641, 1643, 1645, 1647, 1649,
1665, 1667, 1669, 1671, 1673, 1675,
1873, 1875, 1877, 1879, 1881, 1883,

1899, 1901, 1903, 1905, 1907, 1909,
1925, 1927, 1929, 1931, 1933, 1935,
1951, 1953, 1955, 1957, 1959, 1961,
1977, 1979, 1981, 1983, 1985, 1987,
2003, 2005, 2007, 2009, 2011, 2013};

int main (int argc, char* argv[])
{
  double * base = (double*) malloc(sizeof(double)* (2013+12+1));

  if (base == 0)
  {
    printf ("Error in malloc(). Aborting ...\n");
    return 1;  
  }
  double * xa1 = base;
  double * xa2 = xa1 + 12;
  int i;

  // initialize segments touched by indexSet
  for (i =521; i<= 2025; ++i)
  {
    base[i]=0.5*i;
  }

#pragma omp parallel for // default static even scheduling may not trigger data race!
  for (i =0; i< N; ++i) 
  {
    int idx = indexSet[i];
    xa1[idx]+= 1.0;
    xa2[idx]+= 3.0;
  }
  printf("x1[999]=%f xa2[1285]=%f\n", xa1[999], xa2[1285]);
  free (base);
  return  0;
}