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From: "unlvsur at live dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/103565] New: GCC emits more assembly than clang for carry flag Date: Sun, 05 Dec 2021 15:41:42 +0000 [thread overview] Message-ID: <bug-103565-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103565 Bug ID: 103565 Summary: GCC emits more assembly than clang for carry flag Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: unlvsur at live dot com Target Milestone: --- I tried both examples. One emulation with the pattern. Another is with the x86 intrinsic. GCC emits more instructions than clang. https://godbolt.org/z/d15WEY85T https://godbolt.org/z/cob36P8nz Also can GCC be able to understand the pattern of add_carry_pattern just like it understands std::rotl? https://github.com/gcc-mirror/gcc/blob/8d4ef2299cbf9517877dab60d48f34835758a6ee/libstdc%2B%2B-v3/include/std/bit#L135 template<typename T> inline constexpr bool add_carry_pattern(bool carry,T a,T b,T& out) noexcept { T temp{carry+a}; out=temp+b; return (out < b) | (temp < a); } So we do not need that intrinsic anymore and the whole thing can be optimized at SSA level, rather than RTL level??
next reply other threads:[~2021-12-05 15:41 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-12-05 15:41 unlvsur at live dot com [this message] 2021-12-05 15:48 ` [Bug tree-optimization/103565] " unlvsur at live dot com 2021-12-06 21:47 ` pinskia at gcc dot gnu.org 2021-12-06 21:49 ` [Bug target/103565] " pinskia at gcc dot gnu.org 2021-12-06 21:54 ` unlvsur at live dot com
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