RFR: 8349361: C2: RShiftL should support all applicable transformations that RShiftI does [v9]

[Emanuel Peter]

On Mon, 24 Feb 2025 15:18:43 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> 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 15 additional commits since the last revision:
>> 
>>  - review
>>  - review
>>  - review
>>  - Merge branch 'master' into JDK-8349361
>>  - Update src/hotspot/share/opto/mulnode.cpp
>>    
>>    Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>
>>  - Update src/hotspot/share/opto/mulnode.cpp
>>    
>>    Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>
>>  - review
>>  - Update src/hotspot/share/opto/mulnode.hpp
>>    
>>    Co-authored-by: Jasmine Karthikeyan <25208576+jaskarth at users.noreply.github.com>
>>  - Update src/hotspot/share/opto/mulnode.cpp
>>    
>>    Co-authored-by: Jasmine Karthikeyan <25208576+jaskarth at users.noreply.github.com>
>>  - Update src/hotspot/share/opto/mulnode.cpp
>>    
>>    Co-authored-by: Jasmine Karthikeyan <25208576+jaskarth at users.noreply.github.com>
>>  - ... and 5 more: https://git.openjdk.org/jdk/compare/4ffbd68b...5b05d222
>
> src/hotspot/share/opto/mulnode.cpp line 1351:
> 
>> 1349:   const Node* and_node = in(1);
>> 1350:   if (and_node->Opcode() == Op_And(bt) &&
>> 1351:       (mask_t = phase->type(and_node->in(2))->isa_integer(bt)) &&
> 
> Is this an implicit null check?
> 
> Style guide:
>> Do not use ints or pointers as (implicit) booleans with &&, ||, if, while. Instead, compare explicitly, i.e. if (x != 0) or if (ptr != nullptr), etc.

Honestly, why not just split the `if` into 2 ifs.
`const TypeInteger* mask_t;`
That looks a little less than nice as well.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23438#discussion_r1967875020