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From: "pali at kernel dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/114448] New: Roundup not optimized Date: Sun, 24 Mar 2024 14:23:35 +0000 [thread overview] Message-ID: <bug-114448-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114448 Bug ID: 114448 Summary: Roundup not optimized Product: gcc Version: 13.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: pali at kernel dot org Target Milestone: --- https://godbolt.org/z/4fPKGzs1M Straightforward code which round up unsigned number to the next multiply of 4 is: (num % 4 == 0) ? num : num + (4 - num % 4); gcc -O2 generates: mov edx, edi mov eax, edi and edx, -4 add edx, 4 test dil, 3 cmovne eax, edx ret This is not optimal and branch/test can be avoided by using double modulo: num + (4 - num % 4) % 4; for which gcc -O2 generates: mov eax, edi neg eax and eax, 3 add eax, edi ret Optimal implementation for round up 4 is using bithacks: (num + 3) & ~3; for which gcc -O2 generates: lea eax, [rdi+3] and eax, -4 ret
next reply other threads:[~2024-03-24 14:23 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-03-24 14:23 pali at kernel dot org [this message] 2024-03-24 18:54 ` [Bug middle-end/114448] " pinskia at gcc dot gnu.org 2024-03-24 18:55 ` pinskia at gcc dot gnu.org 2024-03-24 19:45 ` pinskia at gcc dot gnu.org
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