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From: "antoshkka at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/114661] New: Bit operations not optimized to multiplication Date: Tue, 09 Apr 2024 16:11:10 +0000 [thread overview] Message-ID: <bug-114661-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114661 Bug ID: 114661 Summary: Bit operations not optimized to multiplication Product: gcc Version: 14.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: antoshkka at gmail dot com Target Milestone: --- Consider the example: unsigned mul(unsigned char c) { if (c > 3) __builtin_unreachable(); return c << 18 | c << 15 | c << 12 | c << 9 | c << 6 | c << 3 | c; } GCC with -O2 generates the following assembly: mul(unsigned char): movzx edi, dil lea edx, [rdi+rdi*8] lea eax, [0+rdx*8] mov ecx, edx sal edx, 15 or eax, edi sal ecx, 9 or eax, ecx or eax, edx ret However it could be optimized to just: mul(unsigned char): imul eax, edi, 299593 ret Compiling with -Os does not help. Godbolt playground: https://godbolt.org/z/YszzMbovK P.S.: without `c << 18 | c << 15 |` the bit operations are transformed to multiplication.
next reply other threads:[~2024-04-09 16:11 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-04-09 16:11 antoshkka at gmail dot com [this message] 2024-04-09 19:55 ` [Bug middle-end/114661] " pinskia at gcc dot gnu.org 2024-04-09 19:57 ` pinskia at gcc dot gnu.org 2024-04-09 22:04 ` pinskia at gcc dot gnu.org
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