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Hasten macro parsing #68848

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wants to merge 4 commits into from
Closed

Hasten macro parsing #68848

wants to merge 4 commits into from

Commits on Feb 10, 2020

  1. Avoid instantiating many Parser structs in generic_extension. 

    Currently, every iteration of the main loop in `generic_extension`
instantiates a `Parser`, which is expensive because `Parser` is a large
type. Many of those instantiations are only used immutably, particularly
for simple-but-repetitive macros of the sort seen in `html5ever` and PR
68836.

This commit initializes a single parser outside the loop, and then uses
`Cow` to avoid cloning it except for the mutating iterations. This
speeds up `html5ever` runs by up to 15%.
    @nnethercote
    nnethercote committed Feb 10, 2020
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  2. Remove the Cow from Directory. 

    The previous commit wrapped `Parser` within a `Cow` for the hot macro
parsing path. As a result, there's no need for the `Cow` within
`Directory`, because it lies within `Parser`.
    @nnethercote
    nnethercote committed Feb 10, 2020
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  3. Change condition ordering in parse_tt. 

    This is a small win, because `Failure` is much more common than
`Success`.
    @nnethercote
    nnethercote committed Feb 10, 2020
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  4. Fix a typo in a variable name.

    @nnethercote
    nnethercote committed Feb 10, 2020
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