https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83017
--- Comment #12 from Dominique d'Humieres <dominiq at lps dot ens.fr> --- > Please use -fopt-info-loop to verify the loop is parallelized. You have > to use -floop-parallelize-all as well due to the cost model issue. If I use the commented loop I get with/without the patch % gfc -Ofast -ftree-parallelize-loops=4 -fopt-info-loop pr83017_db.f90 pr83017_db.f90:28:0: note: loop with 5 iterations completely unrolled (header execution count 379) pr83017_db.f90:26:0: note: loop with 5 iterations completely unrolled (header execution count 1515) pr83017_db.f90:38:0: note: loop with 5 iterations completely unrolled (header execution count 1515) pr83017_db.f90:18:0: note: loop with 4 iterations completely unrolled (header execution count 379) pr83017_db.f90:15:0: note: loop with 5 iterations completely unrolled (header execution count 379) pr83017_db.f90:47:0: note: parallelizing inner loop 6 pr83017_db.f90:24:0: note: basic block vectorized pr83017_db.f90:47:0: note: basic block vectorized % time ./a.out PI 2.98875999 PI 3.14159274 4.027u 0.015s 0:01.02 395.0% 0+0k 0+0io 7pf+0w i.e., a loop is parallelized, and with -floop-parallelize-all % gfc -Ofast -ftree-parallelize-loops=4 -floop-parallelize-all -fopt-info-loop pr83017_db.f90 pr83017_db.f90:28:0: note: loop with 5 iterations completely unrolled (header execution count 379) pr83017_db.f90:26:0: note: loop with 5 iterations completely unrolled (header execution count 1515) pr83017_db.f90:38:0: note: loop with 5 iterations completely unrolled (header execution count 1515) pr83017_db.f90:18:0: note: loop with 4 iterations completely unrolled (header execution count 379) pr83017_db.f90:15:0: note: loop with 5 iterations completely unrolled (header execution count 379) pr83017_db.f90:26:0: note: parallelizing outer loop 3 pr83017_db.f90:24:0: note: basic block vectorized % time ./a.out PI 2.98876095 PI 3.14159274 4.152u 0.011s 0:04.16 100.0% 0+0k 0+0io 0pf+0w i.e., the report says the loop is parallelized, but this is not reflected at run time (for the original test as well).
