[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