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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/95424] Failure to optimize division with numerator of 1 Date: Fri, 28 Jan 2022 18:37:31 +0000 [thread overview] Message-ID: <bug-95424-4-boGLJUeS7P@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-95424-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95424 --- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jeff Law <law@gcc.gnu.org>: https://gcc.gnu.org/g:c2b610e7c6c89fd422c5c31f01023bcddf3cf4a5 commit r12-6924-gc2b610e7c6c89fd422c5c31f01023bcddf3cf4a5 Author: Zhao Wei Liew <zhaoweiliew@gmail.com> Date: Fri Jan 28 13:36:39 2022 -0500 match.pd: Simplify 1 / X for integer X [PR95424] This patch implements an optimization for the following C++ code: int f(int x) { return 1 / x; } int f(unsigned int x) { return 1 / x; } Before this patch, x86-64 gcc -std=c++20 -O3 produces the following assembly: f(int): xor edx, edx mov eax, 1 idiv edi ret f(unsigned int): xor edx, edx mov eax, 1 div edi ret In comparison, clang++ -std=c++20 -O3 produces the following assembly: f(int): lea ecx, [rdi + 1] xor eax, eax cmp ecx, 3 cmovb eax, edi ret f(unsigned int): xor eax, eax cmp edi, 1 sete al ret Clang's output is more efficient as it avoids expensive div operations. With this patch, GCC now produces the following assembly: f(int): lea eax, [rdi + 1] cmp eax, 2 mov eax, 0 cmovbe eax, edi ret f(unsigned int): xor eax, eax cmp edi, 1 sete al ret which is virtually identical to Clang's assembly output. Any slight differences in the output for f(int) is possibly related to a different missed optimization. v2: https://gcc.gnu.org/pipermail/gcc-patches/2022-January/587751.html Changes from v2: 1. Refactor from using a switch statement to using the built-in if-else statement. v1: https://gcc.gnu.org/pipermail/gcc-patches/2022-January/587634.html Changes from v1: 1. Refactor common if conditions. 2. Use build_[minus_]one_cst (type) to get -1/1 of the correct type. 3. Match only for TRUNC_DIV_EXPR and TYPE_PRECISION (type) > 1. gcc/ChangeLog: PR tree-optimization/95424 * match.pd: Simplify 1 / X where X is an integer.
next prev parent reply other threads:[~2022-01-28 18:37 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-29 20:21 [Bug tree-optimization/95424] New: " gabravier at gmail dot com 2020-06-02 6:46 ` [Bug tree-optimization/95424] " rguenth at gcc dot gnu.org 2021-08-14 23:59 ` pinskia at gcc dot gnu.org 2021-12-30 7:12 ` zhaoweiliew at gmail dot com 2021-12-31 1:16 ` zhaoweiliew at gmail dot com 2021-12-31 1:17 ` zhaoweiliew at gmail dot com 2021-12-31 1:18 ` zhaoweiliew at gmail dot com 2021-12-31 1:19 ` zhaoweiliew at gmail dot com 2022-01-05 3:33 ` zhaoweiliew at gmail dot com 2022-01-28 18:37 ` cvs-commit at gcc dot gnu.org [this message] 2022-01-28 18:41 ` law at gcc dot gnu.org 2022-01-29 16:56 ` cvs-commit at gcc dot gnu.org 2024-01-20 17:16 ` pinskia at gcc dot gnu.org
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