8000 [feaLib] more suboptimal compilation of inline multiple sub rules? · Issue #3769 · fonttools/fonttools · GitHub
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[feaLib] more suboptimal compilation of inline multiple sub rules? #3769

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cmyr opened this issue Feb 14, 2025 · 0 comments · May be fixed by #3770
Open

[feaLib] more suboptimal compilation of inline multiple sub rules? #3769

cmyr opened this issue Feb 14, 2025 · 0 comments · May be fixed by #3770

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@cmyr
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cmyr commented Feb 14, 2025

See #3551 for context.

I'm running into something where it looks like feaLib is missing an optimization?

Given the following FEA,

@abc = [a-c];
@def = [d-f];

feature psts {
    lookup test {
        sub @abc' @def @abc by NULL;
    } test;
} psts;

Although feaLib is reusing the contextual lookup, it is creating a new 'rule' for each item in the input class (

fonttools/Lib/fontTools/feaLib/builder.py

Line 1395 in 8a89f4f

chain.rules.append(ChainContextualRule(prefix, [{glyph}], suffix, [sub]))
) even though the items should be able to all share the same rule, since they all have the same target.

I think there's a reasonable solution, here, which is to look for a reusable rule in the same way that we look for a reusable lookup, and I'm going to see if this is trickier than it sounds.
@cmyr cmyr linked a pull request Feb 14, 2025 that will close this issue
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[feaLib] More efficient inline multisub compilation cmyr/fonttools
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