[PATCH] D42851: [sanitizer] Allocator local cache improvements

[Kostya Kortchinsky via Phabricator via llvm-commits]

cryptoad created this revision.
cryptoad added a reviewer: alekseyshl.
Herald added subscribers: Sanitizers, delcypher, kubamracek.

Here are a few improvements proposed for the local cache:

- `InitCache` always read from `per_class_[1]` in the fast path. This was not ideal as we are working with `per_class_[class_id]`. The latter offers the same property we are looking for (eg: `max_count != 0` means initialized), so we might as well use it and keep our memory accesses local to the same `per_class_` element. So change `InitCache` to take the current `PerClass` as an argument. This also makes the fast-path assembly of `Deallocate` a lot more compact;
- Change the 32-bit `Refill` & `Drain` functions to mimic their 64-bit counterparts, by passing the current `PerClass` as an argument. This saves some array computations;
- As far as I can tell, `InitCache` has no place in `Drain`: it's either called from `Deallocate` which calls `InitCache`, or from the "upper" `Drain` which checks for `c->count` to be greater than 0 (strictly). So remove it there.
- Move the `stats_` updates to after we are done with the `per_class_` accesses in an attempt to preserve locality once more;
- Change some `CHECK` to `DCHECK`: I don't think the ones changed belonged in the fast path and seemed to be overly cautious failsafes;
- Mark some variables as `const`.

The overall result is cleaner more compact fast path generated code, and some
performance gains with Scudo (and likely other Sanitizers).


Repository:
  rCRT Compiler Runtime

https://reviews.llvm.org/D42851

Files:
  lib/sanitizer_common/sanitizer_allocator_local_cache.h

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D42851.132616.patch
Type: text/x-patch
Size: 6716 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180202/78bf2496/attachment.bin>