This patch is an optimization for speed: whenever possible, it will avoid creating a new process for the -cc1 invocation, and instead will call the cc1 tool inside the calling process (clang tool).
On Windows, this has a moderate impact on build times (please see timings in the comments below)
CFG (control flow guard) is disabled on Windows.
This patch also mildly improves build times on a Haswell 6-core Linux PC.
@Meinersbur reported no change in timings on a many-core Linux machine.
If you'd like to try this on your configuration, use the script below to ensure a standardized unit of measure:
(this is only for Windows)
Warning: the script pulls and reverts all local changes!
Please edit the script before running, to provide the right filename for applying the patch.
The script can be used such as:
# run the test (lengthy, hours!) > powershell .\abba_test.ps1
By default, it'll do a 2-stage build, including cmake'ing with a fixed set of options; followed by AB/BA testing where it'll alternatively rebuild using Clang 10 with and without the patch, for at least 5 hours. If you want to fiddle the number of hours it runs, you can do:
> powershell .\abba_test.ps1 50
Where '50' represents the number of hours it'll run. You can also skip building the two stages, if you already did it, by setting the second parameter:
> powershell .\abba_test.ps1 50 $True
You then end up with something like that:
Total iterations: 6 | Min | Mean | Median | Max | A | 00:11:55.8588259 | 00:12:11.5531275 | 00:12:09.5867878 | 00:12:30.2468040 | B | 00:09:35.1556958 | 00:09:52.5302980 | 00:09:55.2329476 | 00:10:04.4994028 | Diff | -00:02:20.7031301 | -00:02:19.0228296 | -00:02:14.3538402 | -00:02:25.7474012 |
If you find this useful, I can maybe convert it to a python script and send a review separately.