[cfe-dev] Varying per function optimisation based on include path?

[David Blaikie via cfe-dev]

On Mon, Aug 19, 2019 at 8:34 AM Jon Chesterfield via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hello Clang,
>
> There's a proposal in SG15 (http://wg21.link/p1832) with a suggestion to
> more aggressively inline functions included via isystem when building for
> -Og.
>

To me that sounds pretty outside the scope of the C++ standards committee,
but don't know too much about how they deal with things on the fringe like
this. It would seem simpler/more direct to provide patches/discuss
development in existing compilers to demonstrate the value and leave it up
to "market forces" to handle this sort of quality-of-implementation thing.


> The goal is to improve runtime performance for debug builds that make
> heavy use of the STL.
>
> Does clang already set various attributes based on whether a function was
> found via -i or -isystem, and if not, does that seem a reasonable extension?
>

Nope - pretty sure it doesn't & probably tries fairly hard not to vary code
generation (or even diagnostics, except for a very big slice around system
headers specifically to avoid warnings users can't fix) depending on where
the code was written.

There is work in Clang/LLVM to try to make -Og/-O1 (currently synonymous
and hope to keep them that way as long as possible) be a good/better
fast/debuggable tradeoff. But mostly that centers around avoiding
destructive optimizations & keeping as much debug-ability-related state as
possible.

- Dave


>
> Thanks,
>
> Jon
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20190819/44c053e4/attachment.html>