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From: "hbucher at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/109057] New: Does GCC interpret assembly when deciding to optimize away a variable? Date: Tue, 07 Mar 2023 17:07:18 +0000 [thread overview] Message-ID: <bug-109057-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109057 Bug ID: 109057 Summary: Does GCC interpret assembly when deciding to optimize away a variable? Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: hbucher at gmail dot com Target Milestone: --- I'm trying to figure out why GCC optimizes away a uint8_value that is passed into assembly, basically discarding it. This is in context of Google benchmarks. #include <stdint.h> inline void DoNotOptimize( uint8_t value) { asm volatile("" : : "r,m"(value) : "memory"); } static const uint8_t LUT[8] = {1,5,3,0,2,7,1,2}; void func1(uint8_t val) { DoNotOptimize(LUT[val]); } In this case Gcc generates func1(unsigned char): movzbl %dil, %edi ret More importantly, the entire static array LUT was optimized away from the object file. https://godbolt.org/z/Tab5T84dM Is this the correct behavior in your understanding?
next reply other threads:[~2023-03-07 17:07 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-03-07 17:07 hbucher at gmail dot com [this message] 2023-03-07 17:17 ` [Bug middle-end/109057] " hbucher at gmail dot com 2023-03-07 17:22 ` pinskia at gcc dot gnu.org 2023-03-07 17:27 ` jakub at gcc dot gnu.org 2023-03-07 17:28 ` hbucher at gmail dot com 2023-03-07 17:29 ` jakub at gcc dot gnu.org 2023-03-07 17:31 ` hbucher at gmail dot com 2023-03-07 17:32 ` jakub at gcc dot gnu.org 2023-03-07 17:32 ` pinskia at gcc dot gnu.org 2023-03-07 17:38 ` hbucher at gmail dot com 2023-03-07 17:44 ` jakub at gcc dot gnu.org
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