[llvm-bugs] [Bug 44407] New: Building offloading app is extremely slow

via llvm-bugs llvm-bugs at lists.llvm.org
Sun Dec 29 22:40:50 PST 2019


            Bug ID: 44407
           Summary: Building offloading app is extremely slow
           Product: OpenMP
           Version: unspecified
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: release blocker
          Priority: P
         Component: Runtime Library
          Assignee: unassignedbugs at nondot.org
          Reporter: itaru.kitayama at gmail.com
                CC: llvm-bugs at lists.llvm.org

Building a simple offloading app is extremely slow:
$ cat mini.cpp
#include <stdio.h>
int main() {
        int *a[100];
        *a[0] = 1;

#pragma omp target enter data map(alloc: a[0:100])
#pragma omp target enter data map(to: a[0][0:1])
//#pragma omp target enter data map(to: a[1][0:1])
#pragma omp target parallel for map(to: a[0:100])
        for (int i=0;i<10;i++) {
                printf("%d\n",*a[0]); // accessing the 2nd element of the array


$ time clang++ -g -fopenmp -fopenmp-targets=nvptx64 mini.cpp

real    0m11.355s
user    0m2.843s
sys     0m0.149s

while 9.0.0 clang compiles the same code in 4 secs.

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