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From: "tkoenig at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/101301] Improving sparse switch statement Date: Mon, 05 Jul 2021 05:33:34 +0000 [thread overview] Message-ID: <bug-101301-4-LoLl72TUuJ@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-101301-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101301 --- Comment #6 from Thomas Koenig <tkoenig at gcc dot gnu.org> --- If I create a foo3 function with int foo3 (int n) { if (__builtin_expect_with_probability (n >= 55555, 1, 0.55)) { if (__builtin_expect_with_probability (n >= 77777, 1, 0.33/0.55)) { if (__builtin_expect_with_probability (n == 77777, 1, 0.1/0.33)) return 7; if (__builtin_expect_with_probability (n == 88888, 1, 0.1/0.23)) return 8; if (__builtin_expect_with_probability (n == 99999, 1, 0.1/0.11)) return 9; return 0; } else { if (__builtin_expect_with_probability (n == 55555, 1, 0.1/0.22)) return 5; if (__builtin_expect_with_probability (n == 66666, 1, 0.1/0.11)) return 6; return 0; } } else { if (__builtin_expect_with_probability (n >= 33333, 1, 0.22/0.45)) { if (__builtin_expect_with_probability (n == 33333, 1, 0.1/0.22)) return 3; if (__builtin_expect_with_probability (n == 44444, 1, 0.1/0.11)) return 4; return 0; } else { if (__builtin_expect_with_probability (n == 11111, 1, 0.1/0.23)) return 1; if (__builtin_expect_with_probability (n == 22222, 1, 0.1/0.13)) return 2; return 0; } } } the numbers on POWER9 become [tkoenig@gcc135 ~]$ gcc -O3 bench.c a.c [tkoenig@gcc135 ~]$ ./a.out foo: 7.134855 foo2: 7.842507 foo3: 6.624406 [tkoenig@gcc135 ~]$ gcc -mcpu=native -O3 bench.c a.c [tkoenig@gcc135 ~]$ ./a.out foo: 6.458520 foo2: 7.696735 foo3: 6.196469 where, on a few runs, the differene betweeh foo and foo3 with -mcpu=native sometimes disappears and sometimes is larger (gcc135 is not a benchmark machine). So, I'd say there some advantage in the compiler not lying to itself :-)
next prev parent reply other threads:[~2021-07-05 5:33 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-02 15:32 [Bug tree-optimization/101301] New: " tkoenig at gcc dot gnu.org 2021-07-03 10:41 ` [Bug tree-optimization/101301] " tkoenig at gcc dot gnu.org 2021-07-03 18:42 ` tkoenig at gcc dot gnu.org 2021-07-03 19:34 ` segher at gcc dot gnu.org 2021-07-03 21:57 ` tkoenig at gcc dot gnu.org 2021-07-04 17:37 ` segher at gcc dot gnu.org 2021-07-05 5:33 ` tkoenig at gcc dot gnu.org [this message] 2021-07-05 17:33 ` segher at gcc dot gnu.org 2021-07-06 13:39 ` tkoenig at gcc dot gnu.org 2021-07-06 16:35 ` segher at gcc dot gnu.org 2021-08-12 10:31 ` marxin at gcc dot gnu.org 2022-11-30 13:04 ` cvs-commit at gcc dot gnu.org 2023-04-03 9:04 ` marxin at gcc dot gnu.org
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