We can also avoid forking altogether if should_build() returns false. This
doesn't seem to result in any noticeable speedup, but it's cleaner at least.
dirty_deps() changed its meaning now that we also have to check
state.isbuilt(). Now, just because dirty_deps() returns true doesn't mean
that the file should be unstamped (which forces a rebuild); this might have
happened because of state.isbuilt, which means someone already *did* do a
rebuild.
If we get past state.isbuilt() and into looking at the children, however,
and one of the children is dirty, then we should definitely unstamp the
current target.
If someone else built and marked one of our dependencies, then that
dependency would show up as *clean* in a later redo-ifchange, so other
dependents of that file wouldn't be rebuilt.
We actually have to track two session-specific variables: whether the file
has been checked, and whether it was rebuilt. (Or alternatively, whether it
was dirty when we checked it the first time. But we store the former.)
If a depends on b depends on c, then if when we consider building a, we have
to check b and c. If we then are asked about a2 which depends on b, there
is no reason to re-check b and its dependencies; we already know it's done.
This takes the time to do 'redo t/curse/all' the *second* time down from
1.0s to 0.13s. (make can still do it in 0.07s.)
'redo t/curse/all' the first time is down from 5.4s to to 4.6s. With -j4,
from 3.0s to 2.5s.
This doesn't really seem to change anything, but it's more correct and
should reveal weirdness (especially an incorrect .redo directory in a
sub-redo) sooner.
This makes 'redo -j1000' now run successfully in t/curse, except that we
foolishly generate the same files more than once. But at least not more
than once *in parallel*.
The problem is that redo-ifchange has a different $PWD than its
sub-dependencies, so as it's chasing them down, fixing up the relative paths
totally doesn't work at all.
There's probably a much smarter fix than this, but it's too late at night to
think of it right now.
