[Bug objc/50743] New: [4.7 regression] objc-act.c triggers -Werror=sign-compare breaking bootstrap

["mikpe at it dot uu.se" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50743

             Bug #: 50743
           Summary: [4.7 regression] objc-act.c triggers
                    -Werror=sign-compare breaking bootstrap
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: objc
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mikpe@it.uu.se


Attempting to bootstrap gcc-4.7-20111015 with objc enabled and
--disable-build-poststage1-with-cxx fails with:

/mnt/scratch/gcc-4.7-20111015/gcc/objc/objc-act.c: In function
'check_duplicates':
/mnt/scratch/gcc-4.7-20111015/gcc/objc/objc-act.c:5073:21: error: comparison
between signed and unsigned integer expressions [-Werror=sign-compare]
/mnt/scratch/gcc-4.7-20111015/gcc/objc/objc-act.c:5106:17: error: comparison
between signed and unsigned integer expressions [-Werror=sign-compare]
/mnt/scratch/gcc-4.7-20111015/gcc/objc/objc-act.c: In function
'insert_method_into_method_map':
/mnt/scratch/gcc-4.7-20111015/gcc/objc/objc-act.c:5828:18: error: comparison
between signed and unsigned integer expressions [-Werror=sign-compare]
/mnt/scratch/gcc-4.7-20111015/gcc/objc/objc-act.c:5840:18: error: comparison
between signed and unsigned integer expressions [-Werror=sign-compare]
cc1: all warnings being treated as errors

make[3]: *** [objc/objc-act.o] Error 1
make[3]: Leaving directory `/mnt/scratch/objdir47/gcc'
make[2]: *** [all-stage2-gcc] Error 2
make[2]: Leaving directory `/mnt/scratch/objdir47'
make[1]: *** [stage2-bubble] Error 2
make[1]: Leaving directory `/mnt/scratch/objdir47'
make: *** [bootstrap] Error 2

This is a regression from r179965:
http://gcc.gnu.org/ml/gcc-cvs/2011-10/msg00561.html

The issue is that the code was rewritten to use a number or for-loops with a
size_t index and a TREE_VEC_LENGTH limit; however, TREE_VEC_LENGTH returns a
signed integer, resulting in a signed/unsigned comparison.  The C front-end
catches this error, but the C++ front-end fails to do so due to PR50012.