[PATCH] D98718: [AA][NFC] Convert AliasResult to class containing offset for PartialAlias case.

Fri Mar 19 07:43:40 PDT 2021

dfukalov added a comment.

In D98718#2635171 <https://reviews.llvm.org/D98718#2635171>, @nikic wrote:

> I do see some impact from this patch: https://llvm-compile-time-tracker.com/compare.php?from=be92dcb9f679a23329d360bbc5533acc5f808d9c&to=1f10b8ef5f0243ac0a2679d6f334275471bff316&stat=instructions

I ran additional tests: perf impact of the patch <https://llvm-compile-time-tracker.com/compare.php?from=2bac32f6af511146f6891639557788fcbac0980e&to=fcbbf1460884fbb5aa8b486cea3435af6b50c227&stat=instructions&details=on> and perf impact of the reverting it <https://llvm-compile-time-tracker.com/compare.php?from=5b967c4ce5ef613c11b1ee1479d461cb2da5114e&to=b8d7020d23e977924fee4325a17a8724e7e7cb7f&stat=instructions&details=on>. Here is the "cumulative" (commit patch and revert it back) difference <http://llvm-compile-time-tracker.com/compare.php?from=00fb02a2d215660c330198ae7ab4bad87cb0da98&to=b8d7020d23e977924fee4325a17a8724e7e7cb7f&stat=instructions&details=on>.

Some of tests didn't get back to original values and generated noise comparable with shown average perf drop of the patch. E.g. CMakeFiles/lencod.dir/image.c.o compilation slowed down by 1.79%, but after reverting it got back by 1.28% only. CMakeFiles/lencod.dir/nalucommon.c.o slowed by 0.20% and after reverting //it slowed down again// by enormous 1.29%...

Then I ran image.c.o compilation locally under perf and valgrind. Perf said new compiler slowed down, but valgrind reported tiny speedup.
Btw, both of them reported second topmost self-consuming function 
`DenseMapBase::LookupBucketFor()` mostly called from `DenseMapBase::try_emplace(std::pair<> const&, AAQueryInfo::CacheEntry&&)` and `BasicAAResult::aliasCheck()`.
But again, valgrind said it became faster, perf - slower...

IMHO all of these results say that the reported impact is not significant.
What do you think?

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https://reviews.llvm.org/D98718