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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/103973] x86: 4-way comparison of floats/doubles with spaceship operator possibly suboptimal Date: Tue, 11 Jan 2022 04:55:53 +0000 [thread overview] Message-ID: <bug-103973-4-ax65nnSwm4@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-103973-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103973 --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- With -O2 -fno-trapping-math, we get: ucomisd %xmm1, %xmm0 jp .L9 movl $0, %eax jne .L9 ret .p2align 4,,10 .p2align 3 .L9: ucomisd %xmm0, %xmm1 ja .L12 ucomisd %xmm1, %xmm0 setbe %al addl $1, %eax ret .p2align 4,,10 .p2align 3 .L12: movl $-1, %eax ret With -O2 -fno-trapping-math -ffinite-math-only we get: comisd %xmm1, %xmm0 je .L12 jb .L13 movl $1, %edx movl $2, %eax cmova %edx, %eax ret .p2align 4,,10 .p2align 3 .L12: xorl %eax, %eax ret .p2align 4,,10 .p2align 3 .L13: movl $-1, %eax ret The main reason is NaNs are interesting and trapping comparisons are also interesting. Note LLVM does not implement trapping math at all which is why their code gen is different too.
next prev parent reply other threads:[~2022-01-11 4:55 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-01-11 3:54 [Bug target/103973] New: " nekotekina at gmail dot com 2022-01-11 4:47 ` [Bug target/103973] " crazylht at gmail dot com 2022-01-11 4:49 ` crazylht at gmail dot com 2022-01-11 4:55 ` pinskia at gcc dot gnu.org [this message] 2022-01-11 5:09 ` nekotekina at gmail dot com 2022-01-11 8:52 ` rguenth at gcc dot gnu.org 2022-01-11 19:34 ` jakub at gcc dot gnu.org 2022-01-11 19:46 ` jakub at gcc dot gnu.org 2022-01-14 20:13 ` jakub at gcc dot gnu.org 2022-01-17 12:41 ` cvs-commit at gcc dot gnu.org 2022-01-17 16:41 ` jakub at gcc dot gnu.org 2022-01-18 3:17 ` cvs-commit at gcc dot gnu.org
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