public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "vineetg at rivosinc dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/108987] New: [13 Regression] RISC-V: shiftadd cost model bug needlessly preferring syth_multiply Date: Wed, 01 Mar 2023 19:34:20 +0000 [thread overview] Message-ID: <bug-108987-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108987 Bug ID: 108987 Summary: [13 Regression] RISC-V: shiftadd cost model bug needlessly preferring syth_multiply Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: vineetg at rivosinc dot com Target Milestone: --- gcc trunk is preferring synthetic multiply using shift+add even when they are costlier than multiply. unsigned long long f5(unsigned long long i) { return i * 0x0202020202020202ULL; } riscv64-unknown-linux-gnu-gcc -c -O2 -march=rv64gc_zba f5: slli a5,a0,8 add a0,a5,a0 slli a5,a0,16 add a0,a0,a5 slli a5,a0,32 add a0,a0,a5 slli a0,a0,1 ret With gcc 12.2 this used to be f5: lui a5,%hi(.LC0) ld a5,%lo(.LC0)(a5) mul a0,a0,a5 ret This is a regression introduced by commit f90cb39235c4 ("RISC-V: costs: support shift-and-add in strength-reduction"). It introduced the cost for shift[1-3]+add (to favor SH*ADD) but due to a coding bug ended up doing this for all shift values, affecting synth multiply among others. This showed up as dynamic icount regression in SPEC 531.deepsjeng.
next reply other threads:[~2023-03-01 19:34 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-03-01 19:34 vineetg at rivosinc dot com [this message] 2023-03-01 19:56 ` [Bug target/108987] " vineetg at rivosinc dot com 2023-03-02 10:11 ` rguenth at gcc dot gnu.org 2023-03-06 21:50 ` vineetg at rivosinc dot com
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-108987-4@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).