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c16be7152d
The test programs used by _AC_PROG_CXX_CXX98 and _AC_PROG_CXX_CXX11
can take several seconds to compile, even on current-generation CPUs.
Each of them may be test-compiled up to six times as the configure
script searches for appropriate command-line switches. This is
reported to cancel out all of the other performance gains made since
2.69.
Replace these programs with simpler ones that do not exercise the C++
standard *library* and can be compiled in less than a second each.
On my computer, which is quite new, the minimal configure script
AC_INIT
AC_PROG_CXX
executes in 4.5 seconds (wall-clock) before this change and 0.5
seconds after.
* lib/autoconf/c.m4 (_AC_CXX_CXX98_TEST_HEADER, _AC_CXX_CXX98_TEST_BODY):
Rewrite to test only C++ 1998 language features, not library features.
(_AC_CXX_CXX11_TEST_HEADER, _AC_CXX_CXX11_TEST_BODY):
Similarly for C++ 2011.
* doc/autoconf.texi (AC_PROG_CXX): Document this change.
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| .. | ||
| autoconf.texi | ||
| fdl.texi | ||
| gendocs_template | ||
| gnu-oids.texi | ||
| install.texi | ||
| local.mk | ||
| make-stds.texi | ||
| standards.texi | ||