WIP: experimenting with EH optimizations

[GorNishanov]

Summary

See companion paper: https://isocpp.org/files/papers/P1676R0.pdf
(or https://wg21.link/p1676 after the mailing is published)

This is not intended for real review. Mostly to keep select few appraised of this effort.

[jfb]

https://wg21.link/p1676

404

[jfb]

Tests?

lib/Transforms/IPO/PassManagerBuilder.cpp

348

Nice.

[GorNishanov]

In D63388#1546336, @jfb wrote:

Tests?

Was rushing to the mailing deadline. Will add sometime between now and Cologne.

[GorNishanov]

In D63388#1546335, @jfb wrote:

https://wg21.link/p1676

404

Mailing has not been published yet. I wonder if this link works?

https://isocpp.org/files/papers/P1676R0.pdf

[jfb]

In D63388#1546857, @GorNishanov wrote:

In D63388#1546335, @jfb wrote:

https://wg21.link/p1676

404

Mailing has not been published yet. I wonder if this link works?

https://isocpp.org/files/papers/P1676R0.pdf

Indeed does! Most wonderful, I look forward to optimizations around exception :)

[Bigcheese]

Thanks a lot for working on this. There's a lot of room to improve the performance of exceptions that nobody has done for C++ yet. I've added some reviewers that I'm aware are familiar with the area or that I've talked with about this before.

lib/Transforms/Scalar/CXXSimplifyEH.cpp

624–639

This is a bit concerning. I would much rather either the headers add an attribute saying what they are, or that clang detects what they are and adds an attribute. I don't like llvm interpreting function names.

[Bigcheese]

Also adding the llvm-commits list.

[GorNishanov]

In D63388#1546981, @Bigcheese wrote:

Thanks a lot for working on this. There's a lot of room to improve the performance of exceptions that nobody has done for C++ yet. I've added some reviewers that I'm aware are familiar with the area or that I've talked with about this before.

My apologies for dumping this patch which is very very rough WIP.
I mostly to give a feel of how these optimization might look for those interested.

I hope those who choose to look at it closely would not do more than a cursory look. I intend to do more much more work on it before submitting for real review :-).

[GorNishanov]

lib/Transforms/Scalar/CXXSimplifyEH.cpp

624–639

Yes. I am wondering what is the way of tackling the platform/lib specific naming. One approach to take is to add them to TargetLibraryInfo analysis.

On the other hand. Large number of these optimizations are C++ specific, therefore I am not sure if adding them to TLI make sense.

Possibly a dedicated C++EH helper class that collects and maintains the resolved names for all interesting functions related to C++ EH optimizations across platform / stdlib combinations.