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From: "vgupta at synopsys dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/100363] gcc generating wider load/store than warranted at -O3 Date: Mon, 03 May 2021 18:45:34 +0000 [thread overview] Message-ID: <bug-100363-4-xpjQnlH3rf@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-100363-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100363 --- Comment #15 from Vineet Gupta <vgupta at synopsys dot com> --- (In reply to Linus Torvalds from comment #14) > (In reply to Vineet Gupta from comment #13) > > Sorry the workaround proposed by Alexander doesn't seem to cure it (patch > > attached), outcome is the same > > Vineet - it's not the ldd/std that is necessarily buggy, it's the earlier > tests of the address that guard that vectorized path. > > So your quoted parts of the code generation aren't necessarily the > problematic ones. /me slaps myself. How can I be so stupid. > Did you actually test the code and check whether it has the same issue? > Maybe it changed the address limit guards before that ldd/std? The problem is is indeed gone. I need to analyze the assembly fully how it prevents the bad case. e.g. I'm still not comfortable seeing the loop entered with following and it doing 8 byte ldd/std when we know it should only do 2 at a time. r21 = 0xbf178036 (pre-increment so 0x3e will be first src) r22 = 0xbf1780b2 LPC = 4 80d9a360: lp 12 ;80d9a36c <inflate_fast+0x2c0> 80d9a364: ldd.a r18r19,[r21,8] 80d9a368: std.ab r18r19,[r22,8] > I also sent you a separate patch to test if just upgrading to a newer > version of the zlib code helps. Although that may be buggy for other > reasons, it's not like I actually tested the end result.. But it would be > interesting to hear if that one works for you (again, ldd/std might be a > valid end result of trying to vectorize that code assuming the aliasing > tests are done correctly in the vectorized loop headers). Thx for that. And this seems to boot as well.
next prev parent reply other threads:[~2021-05-03 18:45 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-30 20:09 [Bug c/100363] New: " vgupta at synopsys dot com 2021-04-30 21:43 ` [Bug middle-end/100363] " pinskia at gcc dot gnu.org 2021-04-30 21:44 ` pinskia at gcc dot gnu.org 2021-04-30 21:56 ` vgupta at synopsys dot com 2021-04-30 22:02 ` torvalds@linux-foundation.org 2021-04-30 22:19 ` [Bug tree-optimization/100363] " pinskia at gcc dot gnu.org 2021-04-30 22:20 ` pinskia at gcc dot gnu.org 2021-04-30 22:33 ` vgupta at synopsys dot com 2021-05-01 22:54 ` amonakov at gcc dot gnu.org 2021-05-01 23:09 ` torvalds@linux-foundation.org 2021-05-03 7:41 ` rguenth at gcc dot gnu.org 2021-05-03 16:03 ` torvalds@linux-foundation.org 2021-05-03 16:18 ` torvalds@linux-foundation.org 2021-05-03 17:25 ` vgupta at synopsys dot com 2021-05-03 17:28 ` vgupta at synopsys dot com 2021-05-03 17:47 ` torvalds@linux-foundation.org 2021-05-03 18:45 ` vgupta at synopsys dot com [this message] 2021-05-03 19:43 ` pinskia at gcc dot gnu.org 2021-05-04 6:24 ` rguenth at gcc dot gnu.org 2021-05-04 19:33 ` vgupta at synopsys dot com 2021-05-05 6:32 ` rguenther at suse dot de 2021-05-05 19:59 ` ndesaulniers at google dot com
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