autoconf: Autom4te Cache

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1 20.6 What is `autom4te.cache'?
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1      What is this directory `autom4te.cache'?  Can I safely remove it?
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1    In the GNU Build System, `configure.ac' plays a central role and is
1 read by many tools: `autoconf' to create `configure', `autoheader' to
1 create `config.h.in', `automake' to create `Makefile.in', `autoscan' to
1 check the completeness of `configure.ac', `autoreconf' to check the GNU
1 Build System components that are used.  To "read `configure.ac'"
1 actually means to compile it with M4, which can be a long process for
1 complex `configure.ac'.
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1    This is why all these tools, instead of running directly M4, invoke
1 `autom4te' (⇒autom4te Invocation) which, while answering to a
1 specific demand, stores additional information in `autom4te.cache' for
1 future runs.  For instance, if you run `autoconf', behind the scenes,
1 `autom4te' also stores information for the other tools, so that when
1 you invoke `autoheader' or `automake' etc., reprocessing `configure.ac'
1 is not needed.  The speed up is frequently 30%, and is increasing with
1 the size of `configure.ac'.
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1    But it is and remains being simply a cache: you can safely remove it.
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1 
1      Can I permanently get rid of it?
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1    The creation of this cache can be disabled from `~/.autom4te.cfg',
1 see ⇒Customizing autom4te, for more details.  You should be
1 aware that disabling the cache slows down the Autoconf test suite by
1 40%.  The more GNU Build System components are used, the more the cache
1 is useful; for instance running `autoreconf -f' on the Core Utilities
1 is twice slower without the cache _although `--force' implies that the
1 cache is not fully exploited_, and eight times slower than without
1 `--force'.
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