RFR: 8308103: Massive (up to ~30x) increase in C2 compilation time since JDK 17 [v2]

[Christian Hagedorn]

On Wed, 19 Jul 2023 07:27:15 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> A long chain of nodes are sunk out of a loop. Every time a node is
>> moved out of the loop, a cast is created to pin the node out of the
>> loop. When its input is next sunk, the cast is removed (the cast is
>> replaced by its input) and a new cast is created. Some nodes on the
>> chain have 2 other nodes in the chain as uses. When such a node is
>> sunk, 2 cast nodes are created, one for each use. So as the compiler
>> moves forward in the chain, the number of cast to remove grows. From
>> some profiling, removing those casts is what takes a lot of time.
>> 
>> The fix I propose is, when a node is processed, to check whether a
>> cast at the out of loop control was already created for that node and
>> to reuse it.
>> 
>> The test case takes 6 minutes when I run it without the fix and 3
>> seconds with it.
>
> Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - review
>  - Merge branch 'master' into JDK-8308103
>  - fix & test

Looks good to me, too!

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Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14732#pullrequestreview-1536435561