I belatedly came across the news regarding warp, a C and C++ preproccessor written by Walter Bright in a joint project with Facebook. This has been released under the Boost license and is available at https://github.com/facebook/warp.
The Facebook blog makes the following statement with regards to improved efficiency over the GCC preproccessor
Replacing gcc’s preprocessor with
warphas led to significant improvements of our end-to-end build times (including linking). Depending on a variety of circumstances, we measured debug build speed improvements ranging from 10% all the way to 40%, all in complex projects with massive codebases and many dependencies
The AMA on Reddit and the comments on Hacker News have some interesting commentary on the performance claims, as always with performance measurement and comparison this is a difficult field to navigate.
I am reminded of a recent bottleneck I experienced in the build process of a medium sized project using GCC for an ARM target. The investigation identified the major culprit to be the preprocessing stage, specifically the Search Path for header files was very long. A long Search Path is not something that I would have immediately assumed would be the cause of the bottleneck but other lines of investigation were strongly indicating this was truly the cause.