[Bug c/59802] New: excessive compile time in loop unswitching

[dcb314 at hotmail dot com]

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

            Bug ID: 59802
           Summary: excessive compile time in loop unswitching
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com

Created attachment 31830
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31830&action=edit
gzipped C++ source code

I just compiled the attached code with gcc trunk 20140112 on a x86_64
box with flag -O3 and it took over eight minutes.  Using only -O2 took
a more reasonable 2 minutes 38 seconds.

For reference, the redhat version of gcc 482 took 2 minutes 32 seconds
for -O3 and 2 minutes 11 seconds for -O2.

I can see that for -O2, trunk is using about 30 seconds more CPU time,
which is fine, but for -O3 over 5 minutes more.

I tried flag -ftime-report and here are all the times > 1%.

Execution times (seconds)
 phase opt and generate  : 465.18 (100%) usr   0.50 (57%) sys 468.04 (100%)
wall  130935 kB (59%) ggc
 loop invariant motion   :  22.50 ( 5%) usr   0.01 ( 1%) sys  22.85 ( 5%) wall 
     2 kB ( 0%) ggc
 loop unswitching        : 302.37 (65%) usr   0.01 ( 1%) sys 303.82 (65%) wall 
    72 kB ( 0%) ggc
 CPROP                   :  85.02 (18%) usr   0.09 (10%) sys  85.52 (18%) wall 
  4445 kB ( 2%) ggc
 TOTAL                 : 466.12             0.88           469.55            
221219 kB

Suggest code rework for trunk for -O3, maybe in the area of loop unswitching.

This bug may be a duplicate of bug 38518