• Leszek Swirski's avatar
    [parser] Mark maybe_assigned recursively for shadowing vars · fc4bcce1
    Leszek Swirski authored
    The previous fix for this bug (crrev.com/c/1678365) pessimistically
    would mark all shadowed variables as maybe_assigned. Unfortunately,
    this doesn't work across a parse/preparse boundary, where the shadowing
    variable is found via Scope::AnalyzePartially while the shadowed
    variable is outside of the preparser entry point. In those cases, the
    referencing proxy is copied to the outer scope, in which case the
    dynamicness of the original lookup is lost and the maybe_assigned
    pessimisation no longer applies.
    
    This means that maybe_assigned status of a variable is dependent on
    which function is being parsed. In particular, it can cause bytecode
    to change on recompilation, causing issues for lazy source positions.
    
    This patch allows SetMaybeAssigned to walk its shadowed variables,
    and recursively set them to maybe_assigned too. Checking for
    maybe_assigned changing prevents this recursion from having a
    quadratic performance failure mode.
    
    Bug: v8:8510
    Bug: v8:9394
    Change-Id: Id19fe1fad5ec8f0f9aa03b00eb24497f88f71216
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1677265
    Commit-Queue: Leszek Swirski <leszeks@chromium.org>
    Reviewed-by: 's avatarGeorg Neis <neis@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#62458}
    fc4bcce1
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