libtool performance and shells

[Bob Friesenhahn]

Since it has been claimed that libtool causes a lot of build overhead, 
I have been doing a *lot* of testing here with latest development 
libtool.  We already know that libtool 1.5.X is very slow so it is not 
worth worrying about that and it is more worthwhile to get projects 
migrated to libtool 2.2.X since it is much faster.

Peter O'Gorman came up with a simple useless code parsing benchmark 
which showed that GNU bash could be the Worlds Slowest Shell (TM) 
except for a Korn shell clone called 'pdksh' which never completed at 
all.  Other tests also pointed out that bash seemed to be a bit 
sluggish.  DTrace shows that bash spends an awful lot of time in 
memset() as compared with the other shells.

Simple shell benchmarks seemed to indicate that shells derived from 
the Almquist shell (http://en.wikipedia.org/wiki/Almquist_Shell) were 
the fastest and smallest.  Ksh93 was almost as quick.  Bash was 
slowest at simple contrived benchmarks.

However, there is an old saying "The proof is in the pudding".  I have 
run overall timings of configure and full builds using various shells 
on different systems and found that on average, bash was not 
significantly slower at running the configure script.  I also found 
that bash was not significantly slower for an overall libtool-based 
build.  Bash is never the fastest, but when it is slower there is not 
a significant impact to overall build time.

There are some systems where there is some benefit to using a shell 
other than bash, but the difference does not seem large enough for 
Autoconf and libtool to be concerned enough to use a different shell 
selection algorithm.

Bob
======================================
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/