[Bug tree-optimization/65388] New: Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[Bug tree-optimization/65388] New: Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[maksqwe1 at ukr dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

            Bug ID: 65388
           Summary: Wrong comparison in same_succ_def::equal()
                    tree-ssa-tail-merge.c:590
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: maksqwe1 at ukr dot net

tree-ssa-tail-merge.c:590
same_succ_def::equal()

if (!inverse_flags (e1, e2))
  {
    for (i = 0; i < e1->succ_flags.length (); ++i)
=== >   if (e1->succ_flags[i] != e1->succ_flags[i])
          return 0;
  }

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
That looks indeed.  The code is in mainline as well and I bet 4.8 has it too. 
Patch:

--- a/gcc/tree-ssa-tail-merge.c
+++ b/gcc/tree-ssa-tail-merge.c
@@ -587,7 +587,7 @@ same_succ_def::equal (const value_type *e1, const
compare_type *e2)
   if (!inverse_flags (e1, e2))
     {
       for (i = 0; i < e1->succ_flags.length (); ++i)
-       if (e1->succ_flags[i] != e1->succ_flags[i])
+       if (e1->succ_flags[i] != e2->succ_flags[i])
          return 0;
     }

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #1)
> That looks indeed.

I meant weird.

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Do we warn in this case (something like condition is always false)?
clang has -Wtautological-compare warning that warns say for
int b;
if (b != b)
but doesn't already for
int a[10], i;
if (a[i] != a[i]).
gcc has -Wtype-limits, which partially overlaps the -Wtautological-compare, so
if we introduce it, we should probably just add there the cases not already
covered by -Wtype-limits.

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ah, we have PR54979 for that already...
Marek, would you be interested to look at this in stage1?

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-03-11
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #4)
> Ah, we have PR54979 for that already...
> Marek, would you be interested to look at this in stage1?

Yes, I am; we should be able to warn in such egregious cases.  Similar issues:
PR64249, PR63357.

Taking this one...

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed.

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

--- Comment #8 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Thu Mar 12 08:34:00 2015
New Revision: 221376

URL: https://gcc.gnu.org/viewcvs?rev=221376&root=gcc&view=rev
Log:
PR tree-optimization/65388

Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/tree-ssa-tail-merge.c

--- Comment #9 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Thu Mar 12 08:31:36 2015
New Revision: 221375

URL: https://gcc.gnu.org/viewcvs?rev=221375&root=gcc&view=rev
Log:
PR tree-optimization/65388
* tree-ssa-tail-merge.c (same_succ_def::equal): Fix typo in comparison.

Modified:
    branches/gcc-4_9-branch/gcc/ChangeLog
    branches/gcc-4_9-branch/gcc/tree-ssa-tail-merge.c

[Bug tree-optimization/65388] Wrong comparison in same_succ_def::equal() tree-ssa-tail-merge.c:590

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65388

--- Comment #8 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Thu Mar 12 08:34:00 2015
New Revision: 221376

URL: https://gcc.gnu.org/viewcvs?rev=221376&root=gcc&view=rev
Log:
PR tree-optimization/65388

Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/tree-ssa-tail-merge.c

--- Comment #9 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Thu Mar 12 08:31:36 2015
New Revision: 221375

URL: https://gcc.gnu.org/viewcvs?rev=221375&root=gcc&view=rev
Log:
PR tree-optimization/65388
* tree-ssa-tail-merge.c (same_succ_def::equal): Fix typo in comparison.

Modified:
    branches/gcc-4_9-branch/gcc/ChangeLog
    branches/gcc-4_9-branch/gcc/tree-ssa-tail-merge.c