[bug #15584] 3.81.b4 much slower than 3.80 in some situations

[Boris Kolpackov]

Follow-up Comment #10, bug #15584 (project make):

So I did some mode digging and it appears that make just does what it's
supposed to do. If you look into this makefile carefully you will see the
pattern rule that looks like this %.hi: %.o which pretty much makes every
single .o file depend (directly and inderectly) on all others. Now because
all of the targets in this makefile are intermediate and non-existed, make
dutifully traverses the whole grpath for every .o file and figures out that
it cannot build anyhting. Since it doesn't set any flags like updated or
this_target_is_intermediate_and_does_not_exist_and_i_already_tried_to_build
_it, it does *complete* graph traversal for every .o file it tries to build.
I don't see any way (and don't really want) to fix this in make without doing
a major surgery on of how things work. To summarize, the long time is the
result of three things:

1. Strange desire of the makefile author to have all files intermediate.

2. Pretty much fully-connected dependency graph.

3. Brain-damaged intermediate file logic in GNU make.

I therefore suggest that we leave this corner case alone.

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