facebook warp

[Thiago Farina]

Has anyone looked into using warp preprocessor instead of gcc's preprocessor?

They seem to have achieved good results by using it [1].

[1] - https://code.facebook.com/posts/476987592402291/under-the-hood-warp-a-fast-c-and-c-preprocessor/

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Thiago Farina

[Jeremy Roman]

I haven't looked deeply into it, but at the time it was announced, I heard that Clang still outperformed it.
https://news.ycombinator.com/item?id=7489532 (the author of this post is Google's Daniel Berlin, I believe).

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[Nico Weber]

warp is meant as a replacement for gcc -E, the preprocessor-only mode of the compiler. When using distcc, one needs to quickly figure out which files to upload to the build servers ( http://google-opensource.blogspot.com/2008/08/distccs-pump-mode-new-design-for.html ), and one way to do this is to preprocess the files and see which #includes get processed. But this doesn't require a "full" preprocessor, and I think this is what warp does. (goma also has its own preprocessor for performance reasons, and it's faster than a "real" preprocessor because it does less work.)

So if you're using distcc, this might be useful for you. If you're building locally, this isn't for you.

Nico

[Reid Kleckner]

The main concern for Chromium is that Clang's diagnostics are different after macro expansion. We use this to suppress low-value or false positive warnings in some corner cases. Some users argue that this is a mistake in Clang, but it doesn't change the fact that we can't use warp in Chromium today without triaging a load of warnings.

Clang also provides the -frewrite-includes flag, which prevents macro expansion and only expands includes. I think goma uses it. Warp would need to implement this functionality before we could consider it for Chromium.

On Wed, Feb 25, 2015 at 10:50 AM, Jeremy Roman <jbr...@chromium.org> wrote:

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