[Bug tree-optimization/34148] New: [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[Bug tree-optimization/34148] New: [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

With the fix for PR33870 we now create _loads_ of VOPs for QTs qmake
makefile.cpp
at even -O so that all machines I have either run OOM or with a debug build of
gcc, tree-ssa-sccvn.c:1853 (DFS visiting VUSEs) recurses too deeply and blows
the 8MB stack on x86_64 (and takes too much compile-time).

Which means, we no longer can build QT.


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           Summary: [4.3 Regression] Too many VOPs, too deep tree-ssa-
                    sccvn.c recursion
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: memory-hog, compile-time-hog
          Severity: blocker
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
OtherBugsDependingO 33870
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-11-19 10:51 -------
Created an attachment (id=14577)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14577&action=view)
testcase (unreduced)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[steven at gcc dot gnu dot org]

------- Comment #2 from steven at gcc dot gnu dot org  2007-11-19 11:05 -------
tree-ssa-sccvn should use a non-recursive DFS algorithm.  Though, that is only
part of the solution here, I suppose.


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steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dberlin at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-11-19 11:05:38
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2007-11-19 11:19 -------
Yes, I wonder if we can "cut" the DFS walk somewhere - in this case we have
1000s of stmts with each ~200 VUSEs...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2007-11-19 11:23 -------
One workaround in this case is to run another forwprop / dce between inlining
and the first alias pass.  This get's rid of a lot of pointers and pointed
to temporaries.  Still that doesn't address the fundamental problems here.
(but it makes the testcase work nicely within a bound of 600MB peak
memory usage)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2007-11-19 17:38 -------
With just a forwprop pass after inlining and before salias we miscompile
cp/semantics.c:pop_to_parent_deferring_access_checks() at -O2.
An optimization barrier like

pop_to_parent_deferring_access_checks (void)
{
  if (deferred_access_no_check)
    deferred_access_no_check--; 
  else
    {
      VEC (deferred_access_check,gc) *checks;
      deferred_access *ptr;

      checks = (VEC_last (deferred_access, deferred_access_stack)
                ->deferred_access_checks);

      VEC_pop (deferred_access, deferred_access_stack);
__asm__ __volatile__ ("" : : : "memory");
      ptr = VEC_last (deferred_access, deferred_access_stack);

fixes it.  Reducing max-aliased-vops to 100 (as with -O1 which also passes)
fixes the problem as well.  -O1 -fstrict-aliasing
--param max-aliased-vops=500 (as with -O2) also breaks.  Disabling DOM
makes it work again.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2007-11-20 12:20 -------
http://gcc.gnu.org/ml/gcc-patches/2007-11/msg01046.html fixes the miscompile
of the C++ frontend.

-fno-strict-aliasing makes the testcase consume a lot more memory than
-fstrict-aliasing.  Which is why -O is also a lot worse than -O2.

What one can also notice is that we create lots of unpartitionable SFTs for
structures with just _one_ SFT -- we should not need to create SFTs for those
at all.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2007-11-20 12:21 -------
Created an attachment (id=14585)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14585&action=view)
worse testcase


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2007-11-21 10:16 -------
Subject: Bug 34148

Author: rguenth
Date: Wed Nov 21 10:16:21 2007
New Revision: 130329

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=130329
Log:
2007-11-21  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/34148
        * tree-ssa-structalias.c (create_variable_info_for): Do not use
        field-sensitive PTA for single-element structures.
        * tree-ssa-alias.c (create_overlap_variables_for): Do not create
        SFTs for single-element structures.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-ssa-alias.c
    trunk/gcc/tree-ssa-structalias.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148

[Bug tree-optimization/34148] [4.3 Regression] Too many VOPs, too deep tree-ssa-sccvn.c recursion

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2007-11-21 12:01 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34148