[Bug c/39128] New: GPC polygon clipping library fails with -O2

[Bug c/39128] New: GPC polygon clipping library fails with -O2

[merkert at comcast dot net]

When compiling the popular GPC polygon clipping library
(http://www.cs.man.ac.uk/~toby/alan/software/) with -O2 or -O3 and
then processing a special polygon, it fails with a sigsegv on linux.

The program works fine without optimization and with -O. 
I get the same results with compilers 4.3.2 and 4.3.3, but not with 4.0.2 (at
-O3).

I've run valgrind on the code and it comes back clean and even works!! 

I've attached a the preprocessed source (which is large) from the gcc-4.4. 
This is how it's compile and run:
gcc -O2 -o clip main.i 
gzip -dc polygon.gz | ./clip

I've attached also the full source code.

I'll try to contact the author as well, perhaps there's a problem with the code
when using optimization.


-- 
           Summary: GPC polygon clipping library fails with -O2
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: merkert at comcast dot net
 GCC build triplet: gcc (GCC) 4.4.0 20090130 (experimental)
  GCC host triplet: Linux linux 2.6.11.4-21.17-smp #1 SMP Fri Apr 6 08:42:34
                    UTC 200
GCC target triplet: gcc (GCC) 4.4.0 20090130 (experimental)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

[Bug c/39128] GPC polygon clipping library fails with -O2

[merkert at comcast dot net]

------- Comment #1 from merkert at comcast dot net  2009-02-08 02:17 -------
Created an attachment (id=17268)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17268&action=view)
Preprocessed source

Compile like this: 
gcc -O2 main.i -o clip


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

[Bug c/39128] GPC polygon clipping library fails with -O2

[merkert at comcast dot net]

------- Comment #2 from merkert at comcast dot net  2009-02-08 02:18 -------
Created an attachment (id=17269)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17269&action=view)
The data file that causes the core dump

run like this:

gzip -dc polygon.gz | ./clip


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

[Bug c/39128] GPC polygon clipping library fails with -O2

[merkert at comcast dot net]

------- Comment #3 from merkert at comcast dot net  2009-02-08 02:19 -------
Created an attachment (id=17270)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17270&action=view)
Full source code

Full source code, including main.i and gpc code and the polygon that causes the
core dump.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

[Bug c/39128] GPC polygon clipping library fails with -O2

[merkert at comcast dot net]

------- Comment #4 from merkert at comcast dot net  2009-02-08 02:48 -------
I just found out that it compiles at -O2 if I also specify -ffloat-store. So,
I'm thinking it might be related to that old bug
(http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323), which would not entirely be
a surprise. It's always an issue for any non-trivial piece of math code. 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

[Bug c/39128] GPC polygon clipping library fails with -O2

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2009-02-08 10:25 -------
>From the comments I suggest the code does floating point equality compares,
which is a dangerous thing to do if you are not knowing what you do.  A fix
is to instead of x == y use fabs(x - y) <= epsilon.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  GCC build triplet|gcc (GCC) 4.4.0 20090130    |
                   |(experimental)              |
   GCC host triplet|Linux linux 2.6.11.4-21.17- |
                   |smp #1 SMP Fri Apr 6        |
                   |08:42:34 UTC 200            |
 GCC target triplet|gcc (GCC) 4.4.0 20090130    |
                   |(experimental)              |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

[Bug target/39128] GPC polygon clipping library fails with -O2

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |normal
          Component|c                           |target


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

[Bug target/39128] GPC polygon clipping library fails with -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39128

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE
      Known to fail|                            |

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
As mentioned -ffloat-store works so marking this as a dup of bug 323.  32bit
x86 is less important these days too.

*** This bug has been marked as a duplicate of bug 323 ***