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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/107006] Missing optimization: common idiom for external data Date: Thu, 22 Sep 2022 07:08:08 +0000 [thread overview] Message-ID: <bug-107006-4-CeOnURBGBY@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-107006-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107006 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Component|rtl-optimization |tree-optimization Last reconfirmed| |2022-09-22 Ever confirmed|0 |1 Status|UNCONFIRMED |NEW Keywords| |missed-optimization --- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> --- The reason is that the loops are not unrolled (early enough or at all) for the bswap/load detection. So to work you have to unroll the loops manually or direct GCC to do that, for example inline uint64_t get_le64 (const unsigned char x[64/8]) { uint64_t y = 0; #pragma GCC unroll 8 for (size_t i = 0; i < sizeof y; i++) if (0) y |= (uint64_t)x[i] << ((sizeof y - 1 - i)*8); else y |= (uint64_t)x[i] << i*8; return y; } produces get_le64: .LFB11: .cfi_startproc movq (%rdi), %rax ret the unroll heuristics do not anticipate that later bswap/load detection will merge all the loads and thus not grow code too much.
next prev parent reply other threads:[~2022-09-22 7:08 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-09-22 2:27 [Bug rtl-optimization/107006] New: " hpa at zytor dot com 2022-09-22 2:28 ` [Bug rtl-optimization/107006] " hpa at zytor dot com 2022-09-22 2:28 ` hpa at zytor dot com 2022-09-22 2:28 ` hpa at zytor dot com 2022-09-22 2:29 ` hpa at zytor dot com 2022-09-22 2:30 ` hpa at zytor dot com 2022-09-22 2:30 ` hpa at zytor dot com 2022-09-22 2:30 ` hpa at zytor dot com 2022-09-22 2:31 ` hpa at zytor dot com 2022-09-22 2:32 ` hpa at zytor dot com 2022-09-22 7:08 ` rguenth at gcc dot gnu.org [this message] 2022-09-22 14:26 ` [Bug tree-optimization/107006] " hpa at zytor dot com 2022-09-23 6:11 ` rguenth at gcc dot gnu.org
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