[Bug c/53168] New: ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[Bug c/53168] New: ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[regehr at cs dot utah.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

             Bug #: 53168
           Summary: ICE in find_or_generate_expression, at
                    tree-ssa-pre.c:3053
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: regehr@cs.utah.edu
                CC: chenyang@cs.utah.edu


[regehr@dyson r44]$ current-gcc -c -O2 small.c
small.c: In function 'fn3':
small.c:7:1: internal compiler error: in find_or_generate_expression, at
tree-ssa-pre.c:3053
 fn3 ()
 ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
[regehr@dyson r44]$ cat small.c
int a, b, c;
unsigned *d;
int e[1];
void fn1 ();
int fn2 ();
int
fn3 ()
{
    int *f = &a;
    if (fn2 ())
    {
        for (; c; c++)
        {
            e[a] && (b = 0);
            fn1 ();
            if (e[a])
                return 0;
        }
        for (; c <= 0; c++)
            for (;;)
                ;
    }
    else
        e[0] = 0 != (d = f);
    return *d;
}
[regehr@dyson r44]$ current-gcc -v
Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/uusoc/exports/scratch/regehr/z/compiler-install/gcc-r186954-install/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.8.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/compiler-install/gcc-r186954-install
--program-prefix=r186954- --enable-languages=c,c++
Thread model: posix
gcc version 4.8.0 20120430 (experimental) (GCC)

[Bug tree-optimization/53168] ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-04-30
          Component|c                           |tree-optimization
                 CC|                            |jakub at gcc dot gnu.org
     Ever Confirmed|0                           |1
   Target Milestone|---                         |4.8.0

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-04-30 15:18:05 UTC ---
Started failing with http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=185691

[Bug tree-optimization/53168] ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-05-02 10:31:23 UTC ---
Mine.

[Bug tree-optimization/53168] ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |steven at gcc dot gnu.org

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-05-02 15:00:54 UTC ---
It's what I always wondered about ... we phi-translate again during
do_regular_insertion but we fail to "clean" the result in any way.  So
we end with a translation result that is "invalid", thus one without
a leader and one which we cannot re-create.  That is, valid_in_sets returns
false for it.

Index: gcc/tree-ssa-pre.c
===================================================================
--- gcc/tree-ssa-pre.c  (revision 187042)
+++ gcc/tree-ssa-pre.c  (working copy)
@@ -3617,6 +3619,11 @@ do_regular_insertion (basic_block block,
                                                 vprime, NULL);
              if (edoubleprime == NULL)
                {
+                 if (!valid_in_sets (AVAIL_OUT (bprime), NULL, eprime,
bprime))
+                   {
+                     cant_insert = true;
+                     break;
+                   }
                  avail[bprime->index] = eprime;
                  all_same = false;
                }

Steven - do you by chance remember why "re-translating" during insertion
is ok?  Or is a phi-translation result that cannot be inserted in its
form at the end of the BB bogus (always? or only during insertion?).

[Bug tree-optimization/53168] ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

--- Comment #4 from Steven Bosscher <steven at gcc dot gnu.org> 2012-05-03 08:31:54 UTC ---
I don't remember. Did you look at the paper/thesis to see if it says anything
about this?

[Bug tree-optimization/53168] ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-05-03 14:17:32 UTC ---
I think it is because of how we do VN lookup / insert during phi_translation.
SCCVN does not guarantee availability of its lookup result, thus when
such availability is not guaranteed when we translate things we should rather
use the non-canonical expression (after all we translate expressions (sic!),
not values).

What happens is that we have (simplified)

  if (b)
    {
      x_1 = a;
    }
  else
    {
      if (c)
        for(;;)
          {
            x_2 = a;
            a = 0;
          }
    }

and SCCVN value-numbers x_2 to x_1.  PRE sees that 'a' is ANTIC_IN in the
for (;;) block - but it's not ANTIC_OUT in the if (c) block because it
gets cleaned out there as it is translated as x_1 which is not insertable.

I think the PRE algorithm does not expect that phi_translate (ANTIC_IN (succ))
will ever return something that is _not_ valid at the ANTIC_OUT position.
But our phi-translate implementation happily causes this situation.

My suggested change to check validity of the phi_translate result at
insert time is a workaround, but it only makes this a missed optimization.

This particular case is fixed by not turning the memory reference into
a conversion on translation.

[Bug tree-optimization/53168] ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

--- Comment #6 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-05-04 11:30:39 UTC ---
Author: rguenth
Date: Fri May  4 11:30:35 2012
New Revision: 187153

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=187153
Log:
2012-05-04  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/53168
    * tree-ssa-pre.c (phi_translate_1): Only handle type-punned
    memory reads when the result is a constant we can pun.

    * gcc.dg/torture/pr53168.c: New testcase.
    * gcc.dg/tree-ssa/ssa-pre-30.c: Likewise.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr53168.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-30.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-pre.c

[Bug tree-optimization/53168] ICE in find_or_generate_expression, at tree-ssa-pre.c:3053

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53168

Richard Guenther <rguenth at gcc dot gnu.org> changed:

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

--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-05-04 11:35:25 UTC ---
Fixed.