http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47495
Summary: .mod files: File modification time - Makefile build
issue
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: bur...@gcc.gnu.org
Problem described by Thomas Henlich
at http://gcc.gnu.org/ml/fortran/2011-01/msg00242.html
Currently, gfortran only updates the .mod file (content and file modification
date) if the file changes.
That change has been introduced 2007 with PR 31587
and http://gcc.gnu.org/ml/fortran/2007-04/msg00331.html
The issue is the compilation cascade:
(a) If the source file changes, but the .mod file does not there should be no
recompilation of module USErs required
(b) If the source file changes and a new .o is produced, there is no need to
recompile the source to produce another .mod file with the same
modification
date.
As Thomas' email shows, the current Makefile as written by "gfortran -M" cause
a contiguous recompilation of the source files:
mymodule.o mymodule.mod: mymodule.f90
gfortran -c mymodule.f90
will always recompile the file as "mymodule.mod" stays older than
"mymodule.f90".
On the other hand, for:
myprogram.o: myprogram.f90 mymodule.mod
gfortran -c myprogram.f90
the file will only be recompiled if mymodule.mod actually changes, which is
good.
The question is: How can one solve this properly? Possibly without dating back
the creation date of the .f90 file ...
