re PR fortran/18937 (quadratic behaviour with many label "spaghetti" code)

re PR fortran/18937 (quadratic behaviour with many label "spaghetti" code)

PR fortran/18937
fortran/
* resolve.c: Include obstack.h and bitmap.h.  New variable
labels_obstack.
(code_stack): Add tail and reachable_labels fields.
(reachable_labels): New function.
(resolve_branch): Rework to use new fields in code_stack.
(resolve_code): Call reachable_labels.
(resolve_codes): Allocate and free labels_obstack.
testsuite/
* gfortran.dg/goto_2.f90: New.
* gfortran.dg/goto_3.f90: New.
* gfortran.dg/pr17708.f90: Rename to ...
* gfortran.dg/goto_4.f90: ... this, add comment pointing to
PR.

From-SVN: r123789