[PATCH] [libcxx] Allow the use of ccache when running the test suite.

[Eric Fiselier]

Hi mclow.lists, danalbert, jroelofs,

In order to get the bots running quicker I would like to be able to use ccache 
with the test suite. This patch adds support for running the test suite using 
ccache. To use ccache pass `--param=use_ccache=true` when running the test suite.

ccache will not cache any command that invokes ld, so the build step needs to be
split into two separate compile commands. The cost of splitting the build step
into two parts when not using ccache seems to be minimal. On my machine I saw a
difference of ~5 seconds on a 5 minute test suite run.

A full test suite run with ccache generates about 250MB of cached data.

I recorded the following times for running the test suite in the following configurations:
- no ccache: 340s
- initial ccache run: 380s
- rerun with ccache (no changes): 53s.
- rerun with ccache (<string> changed): 80s
- rerun with ccache (<cmath> changed): 169s
- rerun with ccache (<valarray> changed): 69s

http://reviews.llvm.org/D6647

Files:
  test/lit.cfg

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D6647.17251.patch
Type: text/x-patch
Size: 4034 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20141213/eaca57ec/attachment.bin>