[PATCH] D52193: RFC: [clang] Multithreaded compilation support

[Alexandre Ganea via Phabricator via cfe-commits]

aganea added a comment.

> clang-cl isn't supposed to do (explicit) registry accesses when you hold it right (pass in -fms-compatibility-version etc). Have you seen registry access costs, or is that speculation?

Please see this log: F7268226: clang-cl-log.zip <https://reviews.llvm.org/F7268226> - the child `clang-cl -cc1` takes about ~117ms until it gets into the global initializers. This is on my Haswell PC. On the Skylake, this takes "only" ~60ms.
This probably explains why Ninja is slower on the Skylake when using `clang-cl` as a compiler. There should be a shorter codepath maybe when only a single .cpp is being compiled, and avoid running the child process.


Repository:
  rC Clang

https://reviews.llvm.org/D52193