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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/103252] questionable codegen with kmovd Date: Mon, 15 Nov 2021 17:52:32 +0000 [thread overview] Message-ID: <bug-103252-4-IvKympKmzR@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-103252-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103252 --- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- On https://gcc.godbolt.org/z/KG63ErzEr I don't see anything wrong, ia32 has just a few GPRs and all of them are heavily used in the loop, so if the %k? registers aren't slower than memory, it seems just fine to me. For https://gcc.godbolt.org/z/15hnsb6of trunk emits kmovd %ecx, %k0 movl __libc_tsd_CTYPE_B@gotntpoff(%ebx), %ecx kmovd %k0, %eax movl %gs:(%ecx), %ecx testb $32, 1(%ecx,%eax,2) where it is unclear to me why if RA made the unfortunate decision here to use %k0 doesn't e.g. postreload fix that up, it has: (insn 221 94 95 17 (set (reg:SI 68 k0 [orig:130 c ] [130]) (reg:SI 2 cx [orig:130 c ] [130])) "pr103252.c":81:68 77 {*movsi_internal} (nil)) ... a few insns that don't touch %eax nor %k0 (insn 222 98 197 17 (set (reg:SI 0 ax [orig:130 c ] [130]) (reg:SI 68 k0 [orig:130 c ] [130])) "pr103252.c":81:43 77 {*movsi_internal} (nil)) so why does it the unnecessary hop through another register when it could have movl %ecx, %eax instead of the first kmovd and nothing instead of the second. Those 2 are the only %k0 uses.
next prev parent reply other threads:[~2021-11-15 17:52 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-11-15 14:58 [Bug c/103252] New: " jason at zx2c4 dot com 2021-11-15 15:18 ` [Bug c/103252] " jason at zx2c4 dot com 2021-11-15 17:10 ` jason at zx2c4 dot com 2021-11-15 17:52 ` jakub at gcc dot gnu.org [this message] 2021-11-15 17:59 ` [Bug target/103252] " pinskia at gcc dot gnu.org 2021-11-15 18:07 ` jason at zx2c4 dot com 2021-11-16 1:20 ` crazylht at gmail dot com 2021-11-16 9:29 ` rguenth at gcc dot gnu.org 2021-11-16 11:51 ` jason at zx2c4 dot com 2021-11-16 11:56 ` jakub at gcc dot gnu.org 2021-11-16 12:06 ` jason at zx2c4 dot com 2021-11-18 7:09 ` crazylht at gmail dot com 2021-11-18 8:26 ` crazylht at gmail dot com 2021-11-19 2:42 ` crazylht at gmail dot com 2021-11-19 6:27 ` crazylht at gmail dot com 2021-11-24 5:47 ` crazylht at gmail dot com
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