Computing the language involves computing the source files, which
is an expensive operation. It requires calling
cmMakefile::GetOrCreateSource many times, which involves creating
and matching on many cmSourceFileLocation objects.
Source files of a target may depend on the head-target and the
config as of commit e6971df6 (cmTarget: Make the source files depend
on the config., 2014-02-13). The results are cached for each context
as of commit c5b26f3b (cmTarget: Cache the cmSourceFiles in
GetSourceFiles., 2014-04-05).
Each target in the build graph causes language computation of all
of its dependents with itself as the head-target. This means that
for 'core' libraries on which everything depends, the source files
are computed once for every transitive target-level-dependee and
the result is not cached because the head-target is different. This
was observed in the VTK buildsystem.
Short circuit the computation for targets which have a source-list
that is independent of the head-target. If the source-list has
already been computed and the generator expression evaluation
reports that it was context-independent, return the only source-list
already cached for the target. Reset the short-circuit logic when
sources are added and when the link libraries are re-computed.
Extract upstream KWSys using the following shell commands.
$ git archive --prefix=upstream-kwsys/ 8b085635 | tar x
$ git shortlog --no-merges --abbrev=8 --format='%h %s' 39f98b5d..8b085635
Rolf Eike Beer (2):
a99a9235 set the compile flags for older HP compilers to fix compilation
8b085635 MD5: avoid casting back and forth between size_t and int
Change-Id: I6386b521dbaba2e4f9ed5b2be34a504b9c17fc36
Follow up commit 1de08685 (cmSystemTools: Restore unreachable return to
silence warnings, 2014-04-02) by excluding the unreachable return on the
HP compiler as well as Clang. Both recognize that it is unreachable and
warn.
Expect cxx_variadic_templates to implement N2555.
N2555 is essentially a bugfix and predates most compiler releases which
aimed to experimentally support variadic templates.
