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From: "zhiwuyazhe154 at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/115350] New: Missing optimzation: fold `n = std::min(f ? 0 : 3, -a)` to `n = -a` Date: Wed, 05 Jun 2024 00:53:28 +0000 [thread overview] Message-ID: <bug-115350-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115350 Bug ID: 115350 Summary: Missing optimzation: fold `n = std::min(f ? 0 : 3, -a)` to `n = -a` Product: gcc Version: 15.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: zhiwuyazhe154 at gmail dot com Target Milestone: --- Godbolt Example: https://godbolt.org/z/j9rj5q6W5 Code Example: unsigned short n; #include <algorithm> void fn1( unsigned short f, unsigned char a) { n = std::min(f ? 0 : 3, -a); // equals to "n = -a" } During the operation, -a will be converted to int type, and its value range is [-255, 0], which must be less than 0 or 3, so “n = std::min(f ? 0 : 3, -a)” is equivalent to "n = -a". GCC -O3: fn1(unsigned short, unsigned char): test di, di je .L5 xor eax, eax test sil, sil jne .L5 mov WORD PTR n[rip], ax ret .L5: movzx eax, sil neg eax mov WORD PTR n[rip], ax ret n: .zero 2 Expected code (CLANG -O3): fn1(unsigned short, unsigned char): neg esi mov word ptr [rip + n], si ret n: .short 0
next reply other threads:[~2024-06-05 0:53 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-06-05 0:53 zhiwuyazhe154 at gmail dot com [this message] 2024-06-05 1:09 ` [Bug c++/115350] " pinskia at gcc dot gnu.org 2024-06-05 1:10 ` [Bug tree-optimization/115350] " pinskia at gcc dot gnu.org
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