From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-480179-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 3625 invoked by alias); 12 Mar 2015 15:09:30 -0000
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
Received: (qmail 3530 invoked by uid 48); 12 Mar 2015 15:09:24 -0000
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/44563] GCC uses a lot of RAM when compiling a large numbers of functions
Date: Thu, 12 Mar 2015 15:09:00 -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-Version: 4.3.4
X-Bugzilla-Keywords: compile-time-hog, memory-hog
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields:
Message-ID: <bug-44563-4-GgJvYOxIfl@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-44563-4@http.gcc.gnu.org/bugzilla/>
References: <bug-44563-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-03/txt/msg01323.txt.bz2

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44563

--- Comment #29 from Richard Biener <rguenth at gcc dot gnu.org> ---
Sth like

@@ -672,8 +650,18 @@ cleanup_tree_cfg_bb (basic_block bb)
   if (single_succ_p (bb)
       && can_merge_blocks_p (bb, single_succ (bb)))
     {
-      merge_blocks (bb, single_succ (bb));
-      return true;
+      /* If there is a merge opportunity with the predecessor
+         do nothing now but wait until we process the predecessor.
+        This happens when we visit BBs in a non-optimal order and
+        avoids quadratic behavior with adjusting stmts BB pointer.  */
+      if (single_pred_p (bb)
+         && can_merge_blocks_p (single_pred (bb), bb))
+       ;
+      else
+       {
+         merge_blocks (bb, single_succ (bb));
+         return true;
+       }
     }

   return retval;

in addition should do the job.  Iteration on the predecessor should
cover both merges (so we don't actually need to revisit this block itself).