(automake-1.16.info)Dependency Tracking

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2.2.12 Automatic Dependency Tracking
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Dependency tracking is performed as a side-effect of compilation.  Each
time the build system compiles a source file, it computes its list of
dependencies (in C these are the header files included by the source
being compiled).  Later, any time ‘make’ is run and a dependency appears
to have changed, the dependent files will be rebuilt.

   Automake generates code for automatic dependency tracking by default,
unless the developer chooses to override it; for more information, Note:
Dependencies.

   When ‘configure’ is executed, you can see it probing each compiler
for the dependency mechanism it supports (several mechanisms can be
used):

     ~/amhello-1.0 % ./configure --prefix /usr
     ...
     checking dependency style of gcc... gcc3
     ...

   Because dependencies are only computed as a side-effect of the
compilation, no dependency information exists the first time a package
is built.  This is OK because all the files need to be built anyway:
‘make’ does not have to decide which files need to be rebuilt.  In fact,
dependency tracking is completely useless for one-time builds and there
is a ‘configure’ option to disable this:

‘--disable-dependency-tracking’
     Speed up one-time builds.

   Some compilers do not offer any practical way to derive the list of
dependencies as a side-effect of the compilation, requiring a separate
run (maybe of another tool) to compute these dependencies.  The
performance penalty implied by these methods is important enough to
disable them by default.  The option ‘--enable-dependency-tracking’ must
be passed to ‘configure’ to activate them.

‘--enable-dependency-tracking’
     Do not reject slow dependency extractors.

   Note: Dependency Tracking Evolution,
 for some discussion about the different dependency
tracking schemes used by Automake over the years.