8336759: C2: int counted loop with long limit not recognized as counted loop

[tabjy]

This patch implements 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.

---

Progress

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Issue

• JDK-8336759: C2: int counted loop with long limit not recognized as counted loop (Enhancement - P4)

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[openjdk]

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[tabjy]

/reviewers 2 reviewer

C2 changes

[openjdk]

@tabjy
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 2 Reviewers).