[Bug middle-end/21356] New: Dominance error after aggressive dead code elimination (cd_dce)

[Bug middle-end/21356] New: Dominance error after aggressive dead code elimination (cd_dce)

[loki at gcc dot gnu dot org]

I have internal compiler error for the following c code:
int a;
void* p;

void foo (void)
{
  switch (a)
  {
    a0: case 0:   p = &&a1;
    a1: case 1:   p = &&a2;
    a2: default:  p = &&a1;
  }
  goto *p;
}

Command line:
gcc -c -O2 1.c

Output:
1.c: In function 'foo':
1.c:5: error: dominator of 1 should be 2, not 0
1.c:5: internal compiler error: in verify_dominators, at dominance.c:875
...

-- 
           Summary: Dominance error after aggressive dead code elimination
                    (cd_dce)
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: loki at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: i686-pc-linux-gnu-gcc


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-03 16:00 -------
Confirmed, a regression from 4.0.0.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|middle-end                  |tree-optimization
     Ever Confirmed|                            |1
           Keywords|                            |ice-on-valid-code
   Last reconfirmed|0000-00-00 00:00:00         |2005-05-03 16:00:08
               date|                            |
            Summary|Dominance error after       |[4.1 Regression] Dominance
                   |aggressive dead code        |error after aggressive dead
                   |elimination (cd_dce)        |code elimination (cd_dce)
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-07-06 13:23 -------
Fixed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[dberlin at dberlin dot org]

------- Additional Comments From dberlin at gcc dot gnu dot org  2005-07-06 14:05 -------
Subject: Re:  [4.1 Regression] Dominance error
	after aggressive dead code elimination (cd_dce)

On Tue, 2005-07-05 at 23:29 -0600, Jeffrey A Law wrote:
> DCE in aggressive mode sometimes is able to remove control structures
> and thus edge from the CFG.  Sometimes removal of edges from the CFG
> changes the dominator tree, but we make no attempt to actually keep
> the dominators up-to-date.
> 
> In this testcase failure to keep the dominators up-to-date leads to
> a checking failure.  This is trivially addressed by arranging for the
> dominators to be recomputed if we remove edges from the CFG.  An
> enterprising individual might be able to incrementally update the
> dominators,

Uh, we have code to incrementally update the dominators.
Just use iterate_fix_dominators 



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[rakdver at atrey dot karlin dot mff dot cuni dot cz]

------- Additional Comments From rakdver at atrey dot karlin dot mff dot cuni dot cz  2005-07-07 06:57 -------
Subject: Re:  [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

Hello,

> On Tue, 2005-07-05 at 23:29 -0600, Jeffrey A Law wrote:
> > DCE in aggressive mode sometimes is able to remove control structures
> > and thus edge from the CFG.  Sometimes removal of edges from the CFG
> > changes the dominator tree, but we make no attempt to actually keep
> > the dominators up-to-date.
> > 
> > In this testcase failure to keep the dominators up-to-date leads to
> > a checking failure.  This is trivially addressed by arranging for the
> > dominators to be recomputed if we remove edges from the CFG.  An
> > enterprising individual might be able to incrementally update the
> > dominators,
> 
> Uh, we have code to incrementally update the dominators.
> Just use iterate_fix_dominators 

note however that to use it you must precisely know the set of basic
blocks whose dominators may change (which may or may not be the case
with CDDCE, I haven't thought about it), and the set should rather be
small -- iterate_fix_dominators is O(n^3) in the size of the set.

All in all, if the changes to cfg are indeed rare (which they should be,
given that the problem remained unnoticed so far), just having the
dominators to be recomputed is much easier and safer.

Zdenek


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[dnovillo at gcc dot gnu dot org]

------- Additional Comments From dnovillo at gcc dot gnu dot org  2005-07-08 20:53 -------

The patch for this PR causes bootstrap failures after enabling the new points-to
solver.  I will try to find another solution for this problem.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[dnovillo at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |dnovillo at gcc dot gnu dot
                   |dot org                     |org
             Status|REOPENED                    |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-07-09 17:35 -------
Subject: Bug 21356

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	dnovillo@gcc.gnu.org	2005-07-09 17:35:05

Modified files:
	gcc            : ChangeLog passes.c 

Log message:
	PR 21356
	PR 22332
	* passes.c (execute_todo): Cleanup the CFG before updating
	SSA.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.9394&r2=2.9395
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/passes.c.diff?cvsroot=gcc&r1=2.98&r2=2.99



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356

[Bug tree-optimization/21356] [4.1 Regression] Dominance error after aggressive dead code elimination (cd_dce)

[dnovillo at gcc dot gnu dot org]

------- Additional Comments From dnovillo at gcc dot gnu dot org  2005-07-09 17:38 -------

Fixed.  http://gcc.gnu.org/ml/gcc-patches/2005-07/msg00651.html.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21356