We should probably define CCACHE_CPP2 when using ccache and Clang. See bug 754988.

As part of this, it would also be nice to tackle the general problem of not being able to pass the various CCACHE_* environment variables to ccache. Currently, if you add an export to your .mozconfig (e.g. "export CCACHE_BASEDIR=/Users/gps"), this has no effect (at least if you execute through client.mk - maybe if you launch the Makefile in the objdir directly it works). Furthermore, you can't ac_add_options --with-ccache="CCACHE_BASEDIR=/Users/gps /usr/local/bin/ccache" because configure is testing -e and -z on the string value. Perhaps we could solve this by adding CC_PRE and CXX_PRE or something similar? That would also give us the backdoor to easily proxy all compile commands through another script (e.g. something that intercepted compiler warning output and aggregated information or Clang's scan-build tools). In the current world, getting complex control requires disabling ccache. Just a thought.

I don't have any specifically quantitative evidence to back this up, but it seems that setting CCACHE_CPP2 results in my ccache filling up quicker. We should probably measure this and run it past RelEng before turning this on by default.

(In reply to Gregory Szorc [:gps] from comment #2) > I don't have any specifically quantitative evidence to back this up, but it > seems that setting CCACHE_CPP2 results in my ccache filling up quicker. We > should probably measure this and run it past RelEng before turning this on > by default. Upon further analysis, the results appear to be similar to non-CPP2 builds. Maybe it was CCACHE_BASEDIR (which I set at the same time) affecting things.

Here's a trick I chanced upon: export CC="env ENV_VAR=foo clang"

Comment on attachment 643582 [details] [diff] [review] Define CCACHE_CPP2 when using ccache and Clang Review of attachment 643582 [details] [diff] [review]: ----------------------------------------------------------------- This is beyond my comfort to give feedback on. Mike Hommey has been doing a lot of work on autoconf foo lately and might have some things to say though.

I did some simple benchmarking of my laptop: ccache build 1 real 36m40.916s user 99m18.844s sys 12m22.869s ccache build 2 real 11m53.582s user 9m9.587s sys 3m22.222s no ccache real 32m11.518s user 90m58.849s sys 8m43.691s Which suggests it is worth enabling, but really depends on the cache hit rate we have on try. Do we have any numbers on that?

p.s.: I used a 10GB cache on that benchmark.

Comment on attachment 643582 [details] [diff] [review] Define CCACHE_CPP2 when using ccache and Clang Review of attachment 643582 [details] [diff] [review]: ----------------------------------------------------------------- ::: build/autoconf/compiler-opts.m4 @@ +206,5 @@ > _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} $1$2" > fi > ]) > + > +AC_DEFUN([MOZ_TOOL_VARIABLES], I'd move that in a separate toolchain.m4 file.