https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93535
Bug ID: 93535
Summary: slow float/double simple constant folding with -Ofast
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: hehaochen at hotmail dot com
Target Milestone: ---
Created attachment 47763
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47763&action=edit
testcase
slow float/double simple constant folding with -Ofast compared to -O3
Workload:
Adobe benchmark C++
- simple_types_constant_folding.cpp
- float simple constant folding
- double simple constant folding
(Homebrew GCC 8.3.0_2)
g++-8 -O3 simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 7.40 sec (OK)
double simple constant folding: 7.41 sec (OK)
g++-8 -Ofast simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 8.39 sec SLOW
double simple constant folding: 8.33 sec SLOW
g++-8 -Ofast -fno-fast-math simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 7.43 sec (OK)
double simple constant folding: 7.37 sec (OK)
(Homebrew GCC 9.2.0_3)
g++-9 -O3 simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 7.42 sec (OK)
double simple constant folding: 7.43 sec (OK)
g++-9 -Ofast simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 1.85 sec (OK)
double simple constant folding: 7.43 sec (should be optimized more)
g++-9 -Ofast -fno-fast-math simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 7.49 sec (OK)
double simple constant folding: 7.51 sec (OK)
while, in Apple clang version 11.0.0 (clang-1100.0.33.17):
clang++ -O3 simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 7.59 sec (OK)
double simple constant folding: 7.81 sec (OK)
clang++ -Ofast simple_types_constant_folding.cpp && ./a.out
float simple constant folding: 0.91 sec (OK)
double simple constant folding: 0.90 sec (OK)
