https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96837
Bug ID: 96837
Summary: A false if clause in "omp parallel" seriously affects
the performance
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgomp
Assignee: unassigned at gcc dot gnu.org
Reporter: olaf.krzikalla at dlr dot de
CC: jakub at gcc dot gnu.org
Target Milestone: ---
Created attachment 49148
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49148&action=edit
omp_if_minimal.cpp
Run the attached example without further command line arguments.
Possible output:
Time without false parallel if: 0.0496271
Time with false parallel if: 2.27622
The performance of the second measured call to reduce (below the "omp parallel
if") seems to be affected by the "omp parallel if", altough "argc > 1" resolves
to false. Applies at least to version 7.x and 9.2.
Side note: the intel openmp runtime does not have this issue (no recompiling
necessary).
