[Bug other/54337] New: Dramatic Compilation slow-down on higher Optimizaitons

[nbhargava at google dot com]

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

             Bug #: 54337
           Summary: Dramatic Compilation slow-down on higher Optimizaitons
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: nbhargava@google.com


Created attachment 28061
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28061
Test Case

The attached file contains a few function definitions followed by a main method
with a single line of code duplicated 2500 times.

At optimization levels O0, the code compiles relatively quickly (~8s).
However, at optimization levels O2 and O3, the compilation time jumps to over
30s to compile -- almost a 4x difference.


Interesting things about what speeds up the optimized compilation:

Having an if-statement with an empty body cuts down compilation times on all
optimization levels to under 3s.



This could be related to http://llvm.org/bugs/show_bug.cgi?id=13651, as the
problem was discovered in a file that repeats a macro heavily, as these
examples do.