public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "llvm at rifkin dot dev" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/101701] New: GCC optimization and code generation for if-else chains vs ternary chains vs a switch Date: Fri, 30 Jul 2021 23:37:26 +0000 [thread overview] Message-ID: <bug-101701-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101701 Bug ID: 101701 Summary: GCC optimization and code generation for if-else chains vs ternary chains vs a switch Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: llvm at rifkin dot dev Target Milestone: --- I'm looking at an example of three equivalent functions implemented with if-else chains, ternary chains, and a switch. Gcc is not compiling them equivalently: https://godbolt.org/z/8cjGr7M7W. For the if-else chain, gcc does not optimize away the jumps. For the ternary chain, gcc does its codegen well. For the switch, gcc also does its codegen well but there is an extra mov instruction compared to the ternary chain. I don't think it's idealistic to say these should compile equivalently - if someone told me to prefer one over the other for performance reasons I'd dismiss it as a micro-optimization. Clang does not do this perfectly either at the moment. This bug is probably miscategorized. I am not sure the correct category for it.
next reply other threads:[~2021-07-30 23:37 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-30 23:37 llvm at rifkin dot dev [this message] 2021-07-30 23:39 ` [Bug tree-optimization/101701] " pinskia at gcc dot gnu.org 2021-07-30 23:48 ` pinskia at gcc dot gnu.org 2021-07-30 23:50 ` pinskia at gcc dot gnu.org 2021-07-30 23:53 ` llvm at rifkin dot dev 2021-08-03 9:25 ` marxin at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-101701-4@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).