[libcxx-commits] [PATCH] D137315: [libc++abi] Improve performance of __dynamic_cast

[Sirui Mu via Phabricator via libcxx-commits]

Lancern added a comment.

In D137315#3925193 <https://reviews.llvm.org/D137315#3925193>, @EricWF wrote:

> Do you know why the hint wasn't initially used? Was there a point where compilers didn't actually provide the hints?

I tested some compilers supported by Compiler Explorer and:

- For GCC, the oldest version (4.1.2) supported by Compiler Explorer provides the hints;
- Clang starts providing the hints since version 3.3;
- ICC starts providing the hints since version 19.0.0;
- For ICX, the oldest version (2021.1.2) supported by Compiler Explorer provides the hints.

MSVC is not tested since it does not generate code compatible with the Itanium ABI.

In D137315#3925193 <https://reviews.llvm.org/D137315#3925193>, @EricWF wrote:

> Also, do you think there would be a way to split this change into two? One that does the refactoring without changing behavior, and another (hopefully much smaller) change that starts taking advantage of the src2dst_offset hint?

Actually this revision contains two commits. The first commit starts taking advantage of the `src2dst_offset` hint, and the second commit refactors without changing behavior. Looks like Differential only shows the latest commit in the patch series.

F25325302: 图片.png <https://reviews.llvm.org/F25325302>


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https://reviews.llvm.org/D137315