[Bug middle-end/54337] Dramatic Compilation slow-down on higher Optimizaitons

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54337

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |x86_64-*-*
             Status|UNCONFIRMED                 |RESOLVED
            Version|unknown                     |4.7.1
         Resolution|                            |DUPLICATE

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-08-21 08:09:55 UTC ---
Sort-of "confirmed", though you should expect compile-time increases from -O0
to
-O[123] and I don't think the increases are unreasonable, esp. for C++ code
which
can see a lot if inlining.

> /usr/bin/time g++-4.7 -S -o /dev/null t.C -O0
2.24user 0.09system 0:02.84elapsed 82%CPU (0avgtext+0avgdata
918736maxresident)k
22384inputs+0outputs (97major+62614minor)pagefaults 0swaps
> /usr/bin/time g++-4.7 -S -o /dev/null t.C -O1
11.24user 0.15system 0:11.43elapsed 99%CPU (0avgtext+0avgdata
1045616maxresident)k
0inputs+0outputs (0major+113102minor)pagefaults 0swaps
> /usr/bin/time g++-4.7 -S -o /dev/null t.C -O2
16.67user 0.38system 0:17.12elapsed 99%CPU (0avgtext+0avgdata
1189056maxresident)k
2504inputs+0outputs (11major+199132minor)pagefaults 0swaps
> /usr/bin/time g++-4.7 -S -o /dev/null t.C -O3
17.79user 0.30system 0:18.20elapsed 99%CPU (0avgtext+0avgdata
1203280maxresident)k
328inputs+0outputs (2major+200860minor)pagefaults 0swaps

-O3 time-report:

 alias stmt walking      :   2.87 (16%) usr   0.02 ( 4%) sys   2.96 (16%) wall 
     1 kB ( 0%) ggc
 tree PTA                :   4.59 (26%) usr   0.01 ( 2%) sys   4.63 (25%) wall 
  1313 kB ( 1%) ggc

so I think we have a duplicate for this kind of issue.  SCCVN walks over
non-aliased stores are not limited and can expose quadratic complexity
if there are no aliases in the function that stop the walk.  PR46590
comes to my mind which already tracks this.

*** This bug has been marked as a duplicate of bug 46590 ***