RFR: 8280126: C2: detect and remove dead irreducible loops [v2]

[Emanuel Peter]

On Wed, 11 Jan 2023 18:00:12 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Emanuel Peter 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 two additional commits since the last revision:
>> 
>>  - Merge branch 'master' into JDK-8280126
>>  - 8280126: C2: detect and remove dead irreducible loops
>
> src/hotspot/share/opto/loopnode.cpp line 5173:
> 
>> 5171:         assert(head->loop_status() == RegionNode::LoopStatus::MaybeIrreducibleEntry,
>> 5172:                "head has wrong loop_status");
>> 5173:         assert(!head->is_Loop(), "LoopNode cannot be irreducible loop head");
> 
> It is the same asserts as above. May be move to one function.

Ok, I will move it to a function `RegionNode::as_IrreducibleLoopEntry()`.

> src/hotspot/share/opto/loopnode.cpp line 5256:
> 
>> 5254: }
>> 5255: 
>> 5256: #ifndef PRODUCT
> 
> Should be `#ifdef ASSERT` because it is called in `DEBUG_ONLY()` macro.

👍

> src/hotspot/share/opto/loopnode.cpp line 5280:
> 
>> 5278:           region->loop_status() == RegionNode::LoopStatus::Reducible) {
>> 5279:         failure = true;
>> 5280: #ifdef ASSERT
> 
> No need this.

It was very useful for debugging but can easily be added again.
@vnkozlov if you want me to remove it, I would turn the if-statement into an assert, ok?

> src/hotspot/share/opto/loopnode.hpp line 1067:
> 
>> 1065:   IdealLoopTree *sort( IdealLoopTree *loop, IdealLoopTree *innermost );
>> 1066: 
>> 1067: #ifndef PRODUCT
> 
> ` #ifdef ASSERT`

👍

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PR: https://git.openjdk.org/jdk/pull/11764