[read-fonts] Inline AAT lookup format dispatch - #2109
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Allow format-group inputs to request an inline FontRead dispatcher, and use it for AAT Lookup. This exposes the small format switch across the read-fonts crate boundary without affecting OpenType format groups. Assisted-by: OpenAI Codex <codex@openai.com>
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Interesting that adding inline on all format groups causes a regression. I can only guess that LTO is choosing not to inline coverage and classdef reads as I believe those are the only ones we touch on the OT hot path. Was the regression on Amiri? |
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Yeah as I pushed agents to close more gaps between HB & HR, code gen & inlining decisions showed more and more. I'm open to either option. |
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Motivation
HarfRust repeatedly reconstructs AAT class-lookup views while applying
morxsubtables. The generatedLookup::read_with_argsformat switch issmall, but without an inline hint it remains opaque across the
read-fontscrate boundary.Add an opt-in
#[read_inline]codegen annotation and use it only for theAAT
Lookupformat group. I tested adding the hint to every format group,but that caused a measurable regression in an OpenType workload, so this
keeps the change narrowly scoped.
Performance
With release LTO builds of HarfRust and
benchmark-harf:fa-words.txten-thelittleprince.txten-thelittleprince.txtOn Devanagari Sangam /
hi-words.txt, fixed-iteration hardware countersdropped from 891,866,354 to 879,745,089 instructions. Cycles are sensitive
to final code layout but were about 1–3% lower in repeated runs.
Testing
cargo test --workspace