From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-399338-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 17387 invoked by alias); 23 Aug 2012 11:43:01 -0000
Received: (qmail 17378 invoked by uid 22791); 23 Aug 2012 11:43:00 -0000
X-SWARE-Spam-Status: No, hits=-4.3 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00,KHOP_THREADED
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 23 Aug 2012 11:42:47 +0000
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/46590] [4.6/4.7/4.8 Regression] long compile time with -O2 and many loops
Date: Thu, 23 Aug 2012 11:43:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Keywords: compile-time-hog, memory-hog
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: rguenth at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 4.6.4
X-Bugzilla-Changed-Fields:
Message-ID: <bug-46590-4-IEPx7cNZiy@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-46590-4@http.gcc.gnu.org/bugzilla/>
References: <bug-46590-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
X-SW-Source: 2012-08/txt/msg01610.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46590

--- Comment #31 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-08-23 11:41:50 UTC ---
Btw, I have experimented with

Index: tree-into-ssa.c
===================================================================
--- tree-into-ssa.c     (revision 190594)
+++ tree-into-ssa.c     (working copy)
@@ -3224,11 +3224,35 @@ update_ssa (unsigned update_flags)
       bitmap_head *dfs;

       /* If the caller requested PHI nodes to be added, compute
-        dominance frontiers.  */
+        dominance frontiers for all interesting blocks
+        up to the dominating start_bb.  */
       dfs = XNEWVEC (bitmap_head, last_basic_block);
       FOR_EACH_BB (bb)
        bitmap_initialize (&dfs[bb->index], &bitmap_default_obstack);
-      compute_dominance_frontiers (dfs);
+      EXECUTE_IF_SET_IN_BITMAP (blocks_to_update, 0, i, bi)
+       {
+         basic_block b = BASIC_BLOCK (i);
+         edge_iterator ei;
+         edge p;
+         if (EDGE_COUNT (b->preds) >= 2)
+           FOR_EACH_EDGE (p, ei, b->preds)
+             {
+               basic_block runner = p->src;
+               basic_block domsb;
+               if (runner == start_bb)
+                 continue;
+
+               domsb = get_immediate_dominator (CDI_DOMINATORS, b);
+               while (runner != domsb)
+                 {
+                   if (!bitmap_set_bit (&dfs[runner->index],
+                                        b->index))
+                     break;
+                   runner = get_immediate_dominator (CDI_DOMINATORS,
+                                                     runner);
+                 }
+             }
+       }

       if (sbitmap_first_set_bit (old_ssa_names) >= 0)
        {

which helps reducing the time spent in computing dominance frontiers.  But
as we no longer have bitmaps but bitmap_heads in dfs it's hard to verify
we only ever access dfs for entries we computed ... but we should,
looking at how compute_idf works(?).