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From: "moncef.mechri at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/110551] [11/12/13/14 Regression] an extra mov when doing 128bit multiply Date: Sun, 29 Oct 2023 18:01:00 +0000 [thread overview] Message-ID: <bug-110551-4-h16CPmJfvq@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-110551-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110551 --- Comment #6 from Moncef Mechri <moncef.mechri at gmail dot com> --- I confirm the extra mov disappears thanks to Roger's patch. However, the codegen still seems suboptimal to me when using -march=haswell or newer, even with Roger's patch: uint64_t mulx64(uint64_t x) { __uint128_t r = (__uint128_t)x * 0x9E3779B97F4A7C15ull; return (uint64_t)r ^ (uint64_t)( r >> 64 ); } With -O2: mulx64(unsigned long): movabs rax, -7046029254386353131 mul rdi xor rax, rdx ret With -O2 -march=haswell mulx64(unsigned long): movabs rdx, -7046029254386353131 mulx rdi, rsi, rdi mov rax, rdi xor rax, rsi ret So it looks like there is still one extra mov, since I think the optimal codegen using mulx should be: mulx64(unsigned long): movabs rdx, -7046029254386353131 mulx rax, rsi, rdi xor rax, rsi ret
next prev parent reply other threads:[~2023-10-29 18:01 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-07-04 17:26 [Bug rtl-optimization/110551] New: [11 / 12 / 13 /14 regression] Suboptimal codegen for 128 bits multiplication on x86_64 moncef.mechri at gmail dot com 2023-07-04 17:32 ` [Bug target/110551] [11/12/13/14 " pinskia at gcc dot gnu.org 2023-07-04 17:47 ` [Bug target/110551] [11/12/13/14 Regression] an extra mov when doing 128bit multiply pinskia at gcc dot gnu.org 2023-07-04 18:12 ` moncef.mechri at gmail dot com 2023-07-05 7:06 ` rguenth at gcc dot gnu.org 2023-10-18 19:11 ` roger at nextmovesoftware dot com 2023-10-27 9:05 ` cvs-commit at gcc dot gnu.org 2023-10-29 18:01 ` moncef.mechri at gmail dot com [this message] 2023-11-01 10:06 ` ubizjak at gmail dot com 2023-11-01 22:35 ` cvs-commit at gcc dot gnu.org 2023-11-06 19:24 ` moncef.mechri at gmail dot com 2023-11-12 15:48 ` [Bug target/110551] [11/12/13 " roger at nextmovesoftware dot com
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