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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/104665] Failure to recognize memcpy Date: Wed, 23 Feb 2022 22:35:16 +0000 [thread overview] Message-ID: <bug-104665-4-rQWURCIghn@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-104665-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104665 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2022-02-23 Severity|normal |enhancement Ever confirmed|0 |1 --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- A couple of reasons. First is store merging happens too late. Second reason is store merging does not work in the loop case. Take: #if 1 enum b : unsigned char{}; #else typedef unsigned char b; #endif void serialize_le(b* __restrict dst, const unsigned* __restrict src) { // for (int i = 0; i < 128; ++i, ++src) { unsigned t = *src; *dst++ = static_cast<b>((t >> 0) & 0xff); *dst++ = static_cast<b>((t >> 8) & 0xff); *dst++ = static_cast<b>((t >> 16) & 0xff); *dst++ = static_cast<b>((t >> 24) & 0xff); } } This gets optimized to one load followed by one store. But once you add the loop, and use -fno-tree-vectorize (because GCC's vectorizer gets kicked in which causes other issues), the stores are not merged into one. Also store merging happens way after loop distrubution happens so ...
next prev parent reply other threads:[~2022-02-23 22:35 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-02-23 16:50 [Bug tree-optimization/104665] New: " monad at posteo dot net 2022-02-23 16:51 ` [Bug tree-optimization/104665] " redi at gcc dot gnu.org 2022-02-23 16:55 ` monad at posteo dot net 2022-02-23 22:35 ` pinskia at gcc dot gnu.org [this message] 2022-02-24 9:57 ` rguenth at gcc dot gnu.org
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