public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "steven at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/26944] [4.1/4.2 Regression] -ftree-ch generates worse code Date: Wed, 03 May 2006 21:33:00 -0000 [thread overview] Message-ID: <20060503213309.23611.qmail@sourceware.org> (raw) In-Reply-To: <bug-26944-1008@http.gcc.gnu.org/bugzilla/> ------- Comment #7 from steven at gcc dot gnu dot org 2006-05-03 21:33 ------- Re. comment #5, user code could also have a CFG like that, so we should handle this case properly (and we do, tree-ch is doing the right thing afaict). Re. comment #6, I don't see what the register allocator has to do with this at all. The bottom line is that for the case where we produce good code, IVOPTs selects a simple addressing mode and produces a simple loop exit condition; and for the complicated code, IVOPTs picks an addressing mode that requires a lea and an extra register. Look back at that loop for a moment. With tree-ch, ignoring dead code (the sets to SSA names 5[456] are dead!), the .cunroll dump (i.e. just before IVOPTs) looks like this: # Int_Index_37 = PHI <Int_Index_58(6), Int_Loc_3(4)>; <L0>:; (*pretmp.28_49)[Int_Index_37] = Int_Loc_3; Int_Index_58 = Int_Index_37 + 1; if (D.1563_41 >= Int_Index_58) goto <L8>; else goto <L9>; <L8>:; goto <bb 5> (<L0>); That looks rather nice to me. But just after IVOPTs (in the .ivopts dump) we have turned that simple nice code into this mess: # ivtmp.38_26 = PHI <ivtmp.38_35(6), 0(4)>; <L0>:; D.1622_34 = (int *) pretmp.28_49; D.1623_33 = (int *) Int_1_Par_Val_2; D.1624_22 = (int *) ivtmp.38_26; D.1625_21 = D.1623_33 + D.1624_22; MEM[base: D.1622_34, index: D.1625_21, step: 4B, offset: 20B] = Int_Loc_3; ivtmp.38_35 = ivtmp.38_26 + 1; D.1626_20 = (unsigned int) Int_1_Par_Val_2; D.1627_17 = D.1626_20 + ivtmp.38_35; D.1628_16 = D.1627_17 + 5; Int_Index_15 = (One_Fifty) D.1628_16; if (D.1563_41 >= Int_Index_15) goto <L8>; else goto <L9>; <L8>:; goto <bb 5> (<L0>); If this is caused by the register allocator, I'd like to know why you'd think that. And if this is the doing of tree-ch, then I'd like to know what you expect tree-ch to do instead. But as far as I can tell, this is just a very poor choice by IVOPTs. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26944
next prev parent reply other threads:[~2006-05-03 21:33 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2006-03-30 16:15 [Bug tree-optimization/26944] New: " dann at godzilla dot ics dot uci dot edu 2006-03-30 16:25 ` [Bug tree-optimization/26944] [4.1/4.2 Regression] " rguenth at gcc dot gnu dot org 2006-03-30 16:43 ` dann at godzilla dot ics dot uci dot edu 2006-03-31 22:41 ` Daniel Berlin 2006-03-31 22:41 ` dberlin at dberlin dot org 2006-04-02 8:12 ` pinskia at gcc dot gnu dot org 2006-04-16 19:13 ` mmitchel at gcc dot gnu dot org 2006-05-02 17:38 ` steven at gcc dot gnu dot org 2006-05-03 18:55 ` dann at godzilla dot ics dot uci dot edu 2006-05-03 19:00 ` Andrew Pinski 2006-05-03 19:00 ` pinskia at physics dot uc dot edu 2006-05-03 21:33 ` steven at gcc dot gnu dot org [this message] 2006-05-03 21:53 ` dann at godzilla dot ics dot uci dot edu 2006-05-04 21:25 ` pinskia at gcc dot gnu dot org 2006-05-25 2:39 ` mmitchel at gcc dot gnu dot org 2007-02-14 9:10 ` [Bug tree-optimization/26944] [4.1/4.2/4.3 " mmitchel at gcc dot gnu dot org 2007-06-18 5:28 ` [Bug tree-optimization/26944] [4.1/4.2 " pinskia at gcc dot gnu dot org 2008-07-04 20:22 ` [Bug tree-optimization/26944] [4.2 " jsm28 at gcc dot gnu dot org 2009-03-30 15:51 ` jsm28 at gcc dot gnu dot org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20060503213309.23611.qmail@sourceware.org \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).