Alan W. Irwin wrote:
To summarize, the above quote from GNU make documentation shows they were
concerned about the latency of the "force" alternative to .PHONY. If you
have ever run GNU make in debug mode, there is a lot of stuff it goes
through to look for implicit rules that fit the target so for the very
large
number of Makefile targets that CMake generates that are not files,
there is
a lot of unneeded implicit rule checking going on. That work would be
completely eliminated by appropriate use of .PHONY, and because so many
rules are involved, I suspect that would give a significant reduction in
latency.
We used to have something that removed many implicit rules. I think
that got lost in some version of CMake, it is hard to test... I did
find that there is a command line option to gmake, -r that turns off
implicit rules. I am seeing a speed up with gmake -r. Would it work to
turn off all implicit rules instead of the .PHONY stuff? CMake does not
use any implicit rules anyway. I think the only way to turn them off is
to redefine them as empty rules. This works for all make, and not just
gmake. I am trying to figure out what implicit rules need to be turned
off and how to turn them off. Any ideas?
-Bill
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