[PATCH] D87326: [ADT] Fix reference invalidation when self referencing a SmallVector

Tue Sep 15 01:34:44 PDT 2020

dblaikie added a comment.

In D87326#2273355 <https://reviews.llvm.org/D87326#2273355>, @nikic wrote:

> Tested the newest version of this patch and I'm still seeing **massive** regressions, even larger than before.
>
> Compile-time (instructions retired): https://llvm-compile-time-tracker.com/compare.php?from=cc947207283f934c72af0eb0b1a08978c59d40a2&to=d99c6d441764431519c1c11d490e7e88ffe06775&stat=instructions This is now a 1.4% geomean regression at O3 <https://reviews.llvm.org/owners/package/3/>, with 2% at O3 <https://reviews.llvm.org/owners/package/3/>, with tramp3d-v4 hitting 3%.
>
> Max RSS: https://llvm-compile-time-tracker.com/compare.php?from=cc947207283f934c72af0eb0b1a08978c59d40a2&to=d99c6d441764431519c1c11d490e7e88ffe06775&stat=max-rss This is now a 1.6% geomean regression at O3 <https://reviews.llvm.org/owners/package/3/>, with 2.1% at O0.
>
> Clang text size goes from 80560905 to 82179908, a 2% regression (non-LTO build using GCC 9.3).

@njames93 - mind looking at the memory usage a bit? that's probably relatively easy to check (well, maybe not, since it'll be smeared over all the different instantiations of this template) & seems a bit surprising. Code growth is probably just what it is - but if there's a way to quantify it and check we've got minimal extra instantiations, that'd be good.

The compile-time stat: @nikic: can you measure a wall performance difference? (otherwise possible they're shorter instructions, etc/ doesn't necessarily mean this makes compile times worse, perhaps?)

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