[Bug c/67396] New: [4.9/5.0 regression] Performance regression compiling variadic function with many arguments

["ppluzhnikov at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67396

            Bug ID: 67396
           Summary: [4.9/5.0 regression] Performance regression compiling
                    variadic function with many arguments
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppluzhnikov at google dot com
  Target Milestone: ---

Created attachment 36270
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36270&action=edit
test generator script

For https://sourceware.org/bugzilla/show_bug.cgi?id=18872, I need a test case
that calls printf() with >= 2700 arguments.

GCC-4.9 and 5.0 (and current trunk) take excessively long to compile such test
cases with optimization:

$ perl gen_bz18872.pl 500 > t.c && time gcc-svn-r227321/bin/gcc -c -O2 t.c
user    0m1.506s

$ perl gen_bz18872.pl 1000 > t.c && time gcc-svn-r227321/bin/gcc -c -O2 t.c
user    0m11.976s

$ perl gen_bz18872.pl 2000 > t.c && gcc-svn-r227321/bin/gcc -c -O2 t.c
user    1m40.911s

$ perl gen_bz18872.pl 4000 > t.c && gcc-svn-r227321/bin/gcc -c -O2 t.c
user    14m0.767s  ### Yikes!

For comparison, gcc-4.8 (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4 compiles the 4000
argument case in 1.3s.

The problem is already present in r220312 (the oldest build I have).