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From: "oleg.endo@t-online.de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/51244] SH Target: Inefficient conditional branch Date: Wed, 28 Dec 2011 00:42:00 -0000 [thread overview] Message-ID: <bug-51244-4-qXaTFm0Fvg@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-51244-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51244 --- Comment #4 from Oleg Endo <oleg.endo@t-online.de> 2011-12-27 23:17:03 UTC --- (In reply to comment #1) > > > return a >= 0 && b >= 0 ? c : d; > > x >= 0 is expanded to the sequence like > > ra = not x > rb = -31 > rc = ra >> (neg rb) > T = (rc == 0) > conditional jump > > and combine tries to simplify it. combine simplifies b >= 0 > successfully into shll and bt but fails to simplify a >= 0. > It seems that combine doesn't do constant propagation well and > misses the constant -31. Another simpler fail: int test_func_22_NG (int a, int b, int c, int d) { return a >= 0; } becomes: not r4,r0 ! 9 one_cmplsi2 [length = 2] mov #-31,r1 ! 12 movsi_ie/3 [length = 2] rts ! 31 *return_i [length = 2] shld r1,r0 ! 13 lshrsi3_d [length = 2] which could be: cmp/pz r4 rts movt r0 >From what I could observe, this is caused by the various shift insns which leads combine to this result. For example, the shll, branch sequence that is used instead of cmp/pz, branch is caused by the ashlsi_c insn, which defines a lt:SI comparison. Although that is correct, using cmp/pz could be better, since it does not modify the reg, and on SH4 it is an MT group insn. The ashlsi_c insn / lt:SI picking can be avoided by adjusting the rtx costs, for instance (just tried it out briefly). I think a peephole in this case could fix some of the symptoms but not the actual cause. I'll see if I can come up with something that works without a peephole, even though all the shift stuff looks a bit suspicious ;)
next prev parent reply other threads:[~2011-12-27 23:17 UTC|newest] Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-11-20 20:29 [Bug target/51244] New: " oleg.endo@t-online.de 2011-11-22 23:36 ` [Bug target/51244] " kkojima at gcc dot gnu.org 2011-12-27 22:03 ` oleg.endo@t-online.de 2011-12-27 23:17 ` oleg.endo@t-online.de 2011-12-28 0:42 ` oleg.endo@t-online.de [this message] 2011-12-28 4:57 ` oleg.endo@t-online.de 2011-12-28 16:07 ` oleg.endo@t-online.de 2011-12-28 22:30 ` kkojima at gcc dot gnu.org 2011-12-30 22:18 ` oleg.endo@t-online.de 2012-02-26 23:36 ` olegendo at gcc dot gnu.org 2012-03-02 21:57 ` olegendo at gcc dot gnu.org 2012-03-03 12:32 ` olegendo at gcc dot gnu.org 2012-03-04 17:25 ` olegendo at gcc dot gnu.org 2012-03-05 23:13 ` olegendo at gcc dot gnu.org 2012-03-05 23:38 ` olegendo at gcc dot gnu.org 2012-03-06 8:28 ` olegendo at gcc dot gnu.org 2012-03-06 8:50 ` kkojima at gcc dot gnu.org 2012-03-06 9:48 ` olegendo at gcc dot gnu.org 2012-03-06 10:36 ` kkojima at gcc dot gnu.org 2012-03-06 10:38 ` kkojima at gcc dot gnu.org 2012-03-06 10:39 ` kkojima at gcc dot gnu.org 2012-03-06 10:40 ` kkojima at gcc dot gnu.org 2012-03-06 11:30 ` olegendo at gcc dot gnu.org 2012-03-06 23:43 ` olegendo at gcc dot gnu.org 2012-03-08 1:26 ` olegendo at gcc dot gnu.org 2012-03-08 11:12 ` kkojima at gcc dot gnu.org 2012-03-08 11:15 ` kkojima at gcc dot gnu.org 2012-03-08 11:17 ` kkojima at gcc dot gnu.org 2012-03-09 0:27 ` olegendo at gcc dot gnu.org 2012-03-09 1:45 ` kkojima at gcc dot gnu.org 2012-03-09 8:41 ` kkojima at gcc dot gnu.org 2012-03-09 10:02 ` olegendo at gcc dot gnu.org 2012-03-09 10:37 ` kkojima at gcc dot gnu.org 2012-03-11 13:18 ` olegendo at gcc dot gnu.org 2012-03-15 8:11 ` kkojima at gcc dot gnu.org 2012-03-20 1:46 ` olegendo at gcc dot gnu.org 2012-03-20 2:33 ` kkojima at gcc dot gnu.org 2012-03-20 20:41 ` olegendo at gcc dot gnu.org 2012-05-07 20:53 ` olegendo at gcc dot gnu.org 2012-05-08 21:43 ` olegendo at gcc dot gnu.org 2012-06-30 12:01 ` olegendo at gcc dot gnu.org 2012-07-02 19:24 ` olegendo at gcc dot gnu.org 2012-07-08 15:03 ` olegendo at gcc dot gnu.org 2012-07-23 22:58 ` olegendo at gcc dot gnu.org 2012-07-23 23:29 ` olegendo at gcc dot gnu.org 2012-07-26 0:20 ` olegendo at gcc dot gnu.org 2012-07-30 6:46 ` olegendo at gcc dot gnu.org 2012-08-09 15:55 ` olegendo at gcc dot gnu.org 2012-08-12 22:47 ` olegendo at gcc dot gnu.org 2012-08-20 20:51 ` olegendo at gcc dot gnu.org 2012-08-30 22:54 ` olegendo at gcc dot gnu.org 2012-08-31 10:55 ` kkojima at gcc dot gnu.org 2012-08-31 15:50 ` olegendo at gcc dot gnu.org 2012-09-04 8:03 ` olegendo at gcc dot gnu.org 2012-09-23 21:36 ` [Bug target/51244] [SH] Inefficient conditional branch and code around T bit olegendo at gcc dot gnu.org 2012-09-23 21:42 ` olegendo at gcc dot gnu.org 2012-10-03 21:39 ` olegendo at gcc dot gnu.org 2012-10-12 0:41 ` olegendo at gcc dot gnu.org 2012-10-15 22:08 ` olegendo at gcc dot gnu.org 2012-11-03 12:01 ` olegendo at gcc dot gnu.org 2013-07-18 16:11 ` laurent.alfonsi at st dot com 2013-07-18 16:12 ` laurent.alfonsi at st dot com 2013-07-20 14:38 ` olegendo at gcc dot gnu.org 2013-07-23 8:21 ` laurent.alfonsi at st dot com 2013-07-27 19:28 ` olegendo at gcc dot gnu.org 2013-07-28 8:51 ` olegendo at gcc dot gnu.org 2013-07-28 12:26 ` olegendo at gcc dot gnu.org 2013-07-31 21:46 ` olegendo at gcc dot gnu.org 2013-08-23 0:13 ` olegendo at gcc dot gnu.org 2013-08-23 0:25 ` kkojima at gcc dot gnu.org 2013-09-24 22:43 ` olegendo at gcc dot gnu.org 2013-10-03 22:50 ` olegendo at gcc dot gnu.org 2013-10-12 20:47 ` olegendo at gcc dot gnu.org 2013-10-12 21:26 ` olegendo at gcc dot gnu.org 2013-12-05 17:54 ` olegendo at gcc dot gnu.org 2013-12-06 10:47 ` olegendo at gcc dot gnu.org 2014-05-10 20:19 ` olegendo at gcc dot gnu.org 2014-05-16 22:55 ` olegendo at gcc dot gnu.org 2014-09-13 18:48 ` olegendo at gcc dot gnu.org 2014-11-22 15:07 ` olegendo at gcc dot gnu.org 2014-11-22 15:50 ` olegendo at gcc dot gnu.org 2014-11-22 16:08 ` olegendo at gcc dot gnu.org 2014-12-01 6:50 ` olegendo at gcc dot gnu.org 2014-12-17 22:53 ` olegendo at gcc dot gnu.org 2014-12-17 23:08 ` olegendo at gcc dot gnu.org 2014-12-17 23:15 ` olegendo at gcc dot gnu.org 2014-12-24 21:56 ` olegendo at gcc dot gnu.org 2015-01-24 13:06 ` olegendo at gcc dot gnu.org 2015-03-01 19:16 ` olegendo at gcc dot gnu.org
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