Fix signedness error of max LOS size in C2#348
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qinsoon merged 2 commits intommtk:jdk-21from Mar 23, 2026
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The `PlanConstraints::max_non_los_default_alloc_bytes` constant is a `usize` and can be `usize::MAX` for some plans including NoGC. The C2 code erroneously considered it signed and did signed comparison against object sizes. Consequently, when allocating dynamically sized arrays, the C2-generated code always goes to the slow path. It slows down certain workloads (such as hsqldb and luindex in DaCapo 2006) by 20% in total time. We fix this bug by always performing 64-bit unsigned comparison.
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The `PlanConstraints::max_non_los_default_alloc_bytes` constant is a `usize` and can be `usize::MAX` for some plans including NoGC. The C2 code erroneously considered it signed and did signed comparison against object sizes. Consequently, when allocating dynamically sized arrays, the C2-generated code always goes to the slow path. It slows down certain workloads (such as hsqldb and luindex in DaCapo 2006) by 20% in total time. We fix this bug by always performing 64-bit unsigned comparison. (cherry picked from commit e6dcac0) # Conflicts: # mmtk/Cargo.lock
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The `PlanConstraints::max_non_los_default_alloc_bytes` constant is a `usize` and can be `usize::MAX` for some plans including NoGC. The C2 code erroneously considered it signed and did signed comparison against object sizes. Consequently, when allocating dynamically sized arrays, the C2-generated code always goes to the slow path. It slows down certain workloads (such as hsqldb and luindex in DaCapo 2006) by 20% in total time. We fix this bug by always performing 64-bit unsigned comparison. This is an automatic backport of pull request #348 done by [Mergify](https://mergify.com). --------- Co-authored-by: Kunshan Wang <wks1986@gmail.com>
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The
PlanConstraints::max_non_los_default_alloc_bytesconstant is ausizeand can beusize::MAXfor some plans including NoGC. The C2 code erroneously considered it signed and did signed comparison against object sizes. Consequently, when allocating dynamically sized arrays, the C2-generated code always goes to the slow path. It slows down certain workloads (such as hsqldb and luindex in DaCapo 2006) by 20% in total time.We fix this bug by always performing 64-bit unsigned comparison.