RFR: 8336759: C2: int counted loop with long limit not recognized as counted loop [v3]

[Kangcheng Xu]

On Wed, 4 Dec 2024 16:11:58 GMT, Kangcheng Xu <kxu at openjdk.org> wrote:

>> This patch implements [JDK-8336759](https://bugs.openjdk.org/browse/JDK-8336759) that recognizes int counted loops with long limits.
>> 
>> Currently, patterns like `for ( int i =...; i < long_limit; ...)` where int `i` is implicitly promoted to long (i.e., `(long) i < long_limit`) is not recognized as (int) counted loop. This patch speculatively and optimistically converts long limits to ints and deoptimize if the limit is outside int range, allowing more optimization opportunities. 
>> 
>> In other words, it transforms 
>> 
>> 
>> for (int i = 0; (long) i < long_limit; i++) {...}
>> 
>> 
>> to 
>> 
>> 
>> if (int_min <= long_limit && long_limit <= int_max ) {
>>     for (int i = 0;  i < (int) long_limit; i++) {...}
>> } else {
>>     trap: loop_limit_check
>> }
>> 
>> 
>> This could benefit calls to APIs like `long MemorySegment#byteSize()` when iterating over a long limit.
>
> Kangcheng Xu has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Update src/hotspot/share/opto/loopnode.cpp
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>  - Update src/hotspot/share/opto/loopnode.cpp
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>  - Update src/hotspot/share/opto/loopnode.cpp
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>

Bump. Refactor is WIP

-------------

PR Comment: https://git.openjdk.org/jdk/pull/22449#issuecomment-2568228265