[Bug fortran/47495] .mod files: File modification time - Makefile build issue

["Joost.VandeVondele at pci dot uzh.ch" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47495

--- Comment #5 from Joost VandeVondele <Joost.VandeVondele at pci dot uzh.ch> 2011-01-29 12:02:01 UTC ---
(In reply to comment #4)
> For starters it would be nice if gfortran would even document its precise
> semantics for when module files are created/updated/etc.  I'm sure these
> semantics are not identical across Fortran compilers.  This is PR 42607.

These semantics are definitely not identical across compilers, most compilers
will always write a .mod if a module is compiled (but some generate even no
.mod files or use .MOD or whatever, there is nothing in the Fortran standard
that talks about .mod files). 

However, for me personally, not updating .mod files if they are not changed
(and hence providing a way to avoid recompilation cascades) was one of the most
important reasons to start using gfortran. It can make development
(recompilation) tens of times faster. So, this is absolute a feature to retain
in my opinion.