Chromium & V8 Macro-Optimization Patterns

Proven architectural and engine-level optimization patterns for Speedometer 3 and JetStream.

1. Blink DOM & Layout Engine

Problem: Iterating over DOM collections (childElementCount, firstElementChild, nextElementSibling, slot assignments) causes repeated tree traversal overhead and pointer chases.
Pattern: Flat DOM strip / inline vector batching. Buffer flat child vectors or contiguous arrays to replace $O(N)$ repeated traversal with $O(1)$ direct array index strides.
Key Targets: ElementTraversal, LayoutTreeBuilderTraversal, FlatTreeTraversal.

Problem: Frameworks (e.g. Chart.js) make thousands of consecutive moveTo/lineTo/arc calls per frame, allocating Skia SkPathBuilder verbs on every API invocation.
Pattern: Contiguous coordinate slab buffering (Vector<gfx::PointF, 32>). Defer Skia path building until stroke() or fill(). For single-line strokes (IsLine()), dispatch direct c->drawLine calls to skip path construction entirely.
Key Targets: CanvasPath::LineBuilder, CanvasRenderingContext2DState.

Problem: Frameworks with polymorphic and megamorphic call sites exceed standard primary/secondary stub cache table capacities, causing constant eviction and runtime fallback overhead.
Pattern: Expand kPrimaryTableBits and kSecondaryTableBits in v8/src/ic/stub-cache.h to retain handlers for diverse receiver maps across benchmark iterations.
Key Targets: StubCache, LoadIC, StoreIC, CodeStubAssembler::TryProbeStubCache.

Problem: High-order array builtins (Array.prototype.forEach, Array.prototype.filter, Array.prototype.map) cross boundary accessors, falling back to generic bytecode calls.
Pattern: Unroll dense array loops in Maglev IR / Turboshaft with speculative checks, converting closure invocations to direct JIT-compiled loop strides.
Key Targets: maglev-graph-builder.cc, turboshaft/operations.h.

Problem: Frequent minor GC pauses during micro-allocations in benchmark runner loops.
Pattern: Inline caching, slab allocation for short-lived data structures, and eliminating redundant memory clears in table resizes.