https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86029
Bug ID: 86029 Summary: gcc -O3 make very slow product Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: hg2ecz at ham dot hu Target Milestone: --- I tested a signal processing sample code, and the gcc -O3 give me very slow binary. It's a compiler error or it is good? My CPU is i5-3337u, and I use Ubuntu-18.04 64bit OS. gcc 7.3 and clang 6.0 and I compared with speed of Rust code (rustc 1.24.1) My sample code and test script: $ git clone https://github.com/hg2ecz/smallrx $ cd smallrx/ $ ./gcc-clang-rustc-bench.sh gcc -Ofast -march=native rx.c -lm -o rx-gcc-Ofast real 3.81 user 3.80 sys 0.01 clang -Ofast -march=native rx.c -lm -o rx-clang-Ofast real 6.79 user 6.77 sys 0.02 gcc -O3 -march=native rx.c -lm -o rx-gcc-O3 real 51.76 ----> very slow, clang make faster binary with [-O0, -O1, -O2, -O3] user 51.69 sys 0.07 clang -O3 -march=native rx.c -lm -o rx-clang-O3 real 11.05 user 11.03 sys 0.01 ./Rust/target/release/smallrx real 8.26 user 8.22 sys 0.03