[Bug rtl-optimization/59802] excessive compile time in RTL optimizers (loop unswitching, CPROP)

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59802

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |compile-time-hog
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-01-14
          Component|c                           |rtl-optimization
            Summary|excessive compile time in   |excessive compile time in
                   |loop unswitching            |RTL optimizers (loop
                   |                            |unswitching, CPROP)
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 4.8 shows

 CPROP                   :  45.00 (57%) usr   0.02 ( 4%) sys  45.01 (57%) wall 
  4016 kB ( 2%) ggc
 TOTAL                 :  78.48             0.57            79.04            
213705 kB

while GCC 4.9 has

 loop invariant motion   :  10.11 (11%) usr   0.01 ( 2%) sys  10.16 (11%) wall 
     2 kB ( 0%) ggc
 loop unswitching        :   9.81 (11%) usr   0.00 ( 0%) sys   9.83 (11%) wall 
     1 kB ( 0%) ggc
 CPROP                   :  48.16 (54%) usr   0.04 ( 7%) sys  48.20 (54%) wall 
  4444 kB ( 2%) ggc

so I can't really confirm the unswitching slowness (this is r205857 which
is somewhat older than your test).

Generally I think we should probably consider removing RTL unswitching,
there is not a single loop unswitched by RTL for this testcase.