[llvm-bugs] [Bug 38493] New: Undefined symbol when -polly-parallel is enabled

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https://bugs.llvm.org/show_bug.cgi?id=38493

            Bug ID: 38493
           Summary: Undefined symbol when -polly-parallel is enabled
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Support Libraries
          Assignee: unassignedbugs at nondot.org
          Reporter: m-takahiro at jp.fujitsu.com
                CC: llvm-bugs at lists.llvm.org

When automatic parallelization using polly is applied, a linker outputs an
error:  undefined symbol: GOMP_*.

-------- test.c --------
#include <stdio.h>
#include <math.h>

#define N 300
#define M 4
double a[N][M];
double b[N][M];
double c[N][M];

void foo(int m) {
  int i,j;
  for (j=0; j<N; ++j) {
    for (i=0; i<m; ++i) {
      a[j][i] += b[j][i]*c[j][i];
    }
  }
}

double suma(void) {
  int i,j;
  double s;
  s = 0.0;
  for (j=0; j<N; ++j) {
    for (i=0; i<M; ++i) {
      s += a[j][i];
    }
  }
  return s;
}

#define ANS  (double)300.0000
#define GOSA (double)0.0

int main(void) {
  int i,j;
  double s;
  for (j=0; j<N; ++j) {
    for (i=0; i<M; ++i) {
      a[j][i] = 0.0;
      b[j][i] = 0.5;
      c[j][i] = 0.5;
    }
  }
  foo(M);
  s = suma();
  if (fabs(s - ANS) <= GOSA) {
    printf("ok\n");
  } else {
    printf("ng: %lf != %lf\n", s, ANS);
  }
}
---------------------

$ clang --version
clang version 8.0.0 (trunk 339303)
Target: x86_64-unknown-linux-gnu

$ clang -O3 -mllvm -polly -mllvm -polly-parallel test.c
ld: error: undefined symbol: GOMP_parallel_loop_runtime_start
>>> referenced by 3-P-275_01.c
>>>               /home/takahiro/tmp/3-P-275_01-0c2466.o:(foo)

ld: error: undefined symbol: GOMP_parallel_end
>>> referenced by 3-P-275_01.c
>>>               /home/takahiro/tmp/3-P-275_01-0c2466.o:(foo)

ld: error: undefined symbol: GOMP_loop_runtime_next
>>> referenced by 3-P-275_01.c
>>>               /home/takahiro/tmp/3-P-275_01-0c2466.o:(foo_polly_subfn)

ld: error: undefined symbol: GOMP_loop_runtime_next
>>> referenced by 3-P-275_01.c
>>>               /home/takahiro/tmp/3-P-275_01-0c2466.o:(foo_polly_subfn)

ld: error: undefined symbol: GOMP_loop_end_nowait
>>> referenced by 3-P-275_01.c
>>>               /home/takahiro/tmp/3-P-275_01-0c2466.o:(foo_polly_subfn)


But, If I added -fopenmp option to the above options, the linker didn't output
the error and compilation succeeded. So, when -polly-parallel option is
specified, should I need to specify -fopenmp option? Or, should clang pass
"-lomp" to the linker implicitly?

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