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From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/109088] GCC does not always vectorize conditional reduction Date: Wed, 27 Sep 2023 02:58:51 +0000 [thread overview] Message-ID: <bug-109088-4-tHldMzFDoZ@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-109088-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109088 --- Comment #8 from JuzheZhong <juzhe.zhong at rivai dot ai> --- It's because the order of the operations we are doing: For code as follows: result += mask ? a[i] + x : 0; GCC: result_ssa_1 = PHI <result_ssa_2, 0> ... STMT 1. tmp = a[i] + x; STMT 2. tmp2 = tmp + result_ssa_1; STMT 3. result_ssa_2 = mask ? tmp2 : result_ssa_1; Here we can see both STMT 2 and STMT 3 are using 'result_ssa_1', we end up with 2 uses of the PHI result. Then, we failed to vectorize. Wheras LLVM: result_ssa_1 = PHI <result_ssa_2, 0> ... IR 1. tmp = a[i] + x; IR 2. tmp2 = mask ? tmp : 0; IR 3. result_ssa_2 = tmp2 + result_ssa_1. LLVM only has 1 use. Is it reasonable to swap the order in match.pd ?
next prev parent reply other threads:[~2023-09-27 2:58 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-03-10 9:24 [Bug c/109088] New: GCC fail auto-vectorization juzhe.zhong at rivai dot ai 2023-03-10 10:39 ` [Bug c/109088] " ubizjak at gmail dot com 2023-03-10 12:39 ` [Bug tree-optimization/109088] " rguenth at gcc dot gnu.org 2023-03-10 13:16 ` juzhe.zhong at rivai dot ai 2023-03-10 14:04 ` pinskia at gcc dot gnu.org 2023-03-10 14:09 ` [Bug tree-optimization/109088] GCC does not always vectorize conditional reduction pinskia at gcc dot gnu.org 2023-09-26 12:14 ` juzhe.zhong at rivai dot ai 2023-09-27 2:45 ` juzhe.zhong at rivai dot ai 2023-09-27 2:58 ` juzhe.zhong at rivai dot ai [this message] 2023-09-27 7:15 ` rguenth at gcc dot gnu.org 2023-09-27 7:34 ` juzhe.zhong at rivai dot ai 2023-09-27 9:06 ` rguenth at gcc dot gnu.org 2023-09-27 9:27 ` juzhe.zhong at rivai dot ai 2023-09-27 14:11 ` juzhe.zhong at rivai dot ai 2023-10-06 9:44 ` rguenth at gcc dot gnu.org 2023-11-10 12:02 ` juzhe.zhong at rivai dot ai 2023-11-10 13:10 ` rguenth at gcc dot gnu.org 2023-11-10 13:42 ` juzhe.zhong at rivai dot ai 2023-11-15 14:09 ` rguenth at gcc dot gnu.org 2023-11-15 14:38 ` juzhe.zhong at rivai dot ai 2023-11-15 14:42 ` rguenther at suse dot de 2023-11-16 1:06 ` juzhe.zhong at rivai dot ai 2023-11-16 6:50 ` rguenther at suse dot de
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