https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87251
Bug ID: 87251
Summary: warn about unnecessary USE statements
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: janus at gcc dot gnu.org
Target Milestone: ---
It would be nice if gfortran had diagnostics to warn about unnecessary USE
statements, e.g. via a flag "-Wunused-module" or similar (analogous to the
flags that warn about unused variables, parameters or dummy arguments).
In small program, extraneous USE statements are usually easy to detect and
don't do much harm. In a large code base with many modules and dependencies, it
becomes increasingly harder to check all of them and get rid of unnecessary
ones.
One harmful effect of extra USE statements can be an increase of compile time
by additional module dependencies, or also by strongly increasing the number of
symbols that a compiler has to deal with in a given namespace (for large
modules with default public accessibility, such effects can quickly potentiate
in dependency chains).
Simple test case (where the dependency of 'b' on 'a' is for real, while the
dependency of 'c' on 'a' is bogus and can be removed):
module a
integer :: x,y,z
contains
subroutine sub()
end subroutine
end
module b
use a
contains
subroutine tub
call sub
end subroutine
end module
module c
use a
contains
subroutine cub
print *, "..."
end subroutine
end module
