[Bug preprocessor/44526] New: libcpp should avoid circular dependencies

["dfranke at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Since r160684 gfortran supports generation of Makefile dependencies via libcpp.

In the example below, foo.mod is a target as it is generated from the .f90
file, but also a dependency as it used in the same source file:

$ cat foo.f90
MODULE foo
END MODULE
USE foo
END

$ gfortran-svn -cpp -M foo.f90
foo.o foo.mod: foo.f90 foo.mod

Make complains about (and drops) the circular dependency.

This could be improved if mkdeps.c (deps_add_dep) would verify that there is no
target of the same name and if there is, would drop the dependency. This
assumes that there is no situation where such a circular dependency would be
actually required.

The case that a target is generated with a respective dependency in place does
not happen in Fortran - to USE a module, it must have been seen before, i.e.
the module file must exist.

Suggested patch:

Index: libcpp/mkdeps.c
===================================================================
--- libcpp/mkdeps.c     (revision 160677)
+++ libcpp/mkdeps.c     (working copy)
@@ -256,8 +256,18 @@ deps_add_default_target (struct deps *d,
 void
 deps_add_dep (struct deps *d, const char *t)
 {
+  unsigned int i;
+
   t = munge (apply_vpath (d, t));  /* Also makes permanent copy.  */

+  /* Avoid circular dependencies.  */
+  for (i = 0; i < d->ntargets; i++)
+    if (strcmp (d->targetv[i], t) == 0)
+      {
+       free ((void *) t);
+       return;
+      }
+
   if (d->ndeps == d->deps_size)
     {
       d->deps_size = d->deps_size * 2 + 8;


-- 
           Summary: libcpp should avoid circular dependencies
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: patch
          Severity: enhancement
          Priority: P3
         Component: preprocessor
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dfranke at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44526