• Caitlin Potter's avatar
    Reland "[esnext] load `iterator.next` only once at beginning of iteration" · 2d889aa9
    Caitlin Potter authored
    https://github.com/tc39/ecma262/pull/988 gained concensus during the
    september 2017 TC39 meetings. This moves the load of the "next" method
    to the very beginning of the iteration protocol, rather than during
    each iteration step.
    
    This impacts:
    
    - yield*
    - for-of loops
    - spread arguments
    - array spreads
    
    In the v8 implementation, this also affects async iteration versions of
    these things (the sole exception being the Async-From-Sync iterator,
    which requires a few more changes to work with this, likely done in a
    followup patch).
    
    This change introduces a new AST node, ResolvedProperty, which can be used
    as a callee by Call nodes to produce the same bytecode as Property calls,
    without observably re-loading the property. This is used in several
    AST-desugarings involving the iteration protocol.
    
    BUG=v8:6861, v8:5699
    R=rmcilroy@chromium.org
    TBR=neis@chromium.org, adamk@chromium.org
    
    Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
    Change-Id: I9685db6e85315ba8a2df87a4537c2bf491e1e35b
    Reviewed-on: https://chromium-review.googlesource.com/857593
    Commit-Queue: Caitlin Potter <caitp@igalia.com>
    Reviewed-by: 's avatarRoss McIlroy <rmcilroy@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#50518}
    2d889aa9
for-of-loops-expected.txt 9.13 KB