• Maya Lekova's avatar
    Revert "cppgc-js: Add snapshot for C++ objects" · fba14bde
    Maya Lekova authored
    This reverts commit 02849fd9.
    
    Reason for revert: Breaks Win64 MSVC bot and closes the tree - https://ci.chromium.org/p/v8/builders/ci/V8%20Win64%20-%20msvc/15416
    
    Original change's description:
    > cppgc-js: Add snapshot for C++ objects
    >
    > The following implements a snapshotting algorithm for C++ objects that
    > also filters strongly-connected components (SCCs) of only "hidden"
    > objects that are not (transitively) referencing any non-hidden
    > objects.
    >
    > C++ objects come in two versions.
    > a. Named objects that have been assigned a name through NameProvider.
    > b. Unnamed objects, that are potentially hidden if the build
    >    configuration requires Oilpan to hide such names. Hidden objects have
    >    their name set to NameProvider::kHiddenName.
    >
    > The main challenge for the algorithm is to avoid blowing up the final
    > object graph with hidden nodes that do not carry information. For that
    > reason, the algorithm filters SCCs of only hidden objects, e.g.:
    >   ...  -> (object) -> (object) -> (hidden) -> (hidden)
    > In this case the (hidden) objects are filtered from the graph. The
    > trickiest part is maintaining visibility state for objects referencing
    > other objects that are currently being processed.
    >
    > Main algorithm idea (two passes):
    > 1. First pass marks all non-hidden objects and those that transitively
    >    reach non-hidden objects as visible. Details:
    >    - Iterate over all objects.
    >    - If object is non-hidden mark it as visible and also mark parent
    >      as visible if needed.
    >    - If object is hidden, traverse children as DFS to find non-hidden
    >      objects. Post-order process the objects and mark those objects as
    >      visible that have child nodes that are visible themselves.
    >    - Maintain an epoch counter (StateStorage::state_count_) to allow
    >      deferring the visibility decision to other objects in the same
    >      SCC. This is similar to the "lowlink" value in Tarjan's algorithm
    >      for SCC.
    >    - After the first pass it is guaranteed that all deferred
    >      visibility decisions can be resolved.
    > 2. Second pass adds nodes and edges for all visible objects.
    >    - Upon first checking the visibility state of an object, all deferred
    >      visibility states are resolved.
    >
    > For practical reasons, the recursion is transformed into an iteration.
    > We do not use plain Tarjan's algorithm to avoid another pass over
    > all nodes to create SCCs.
    >
    > Follow ups:
    > 1. Adding wrapper nodes for cpp objects that are wrappables for V8
    >    wrappers.
    > 2. Adding detachedness information.
    >
    > Change-Id: I6e127d2c6d65e77defe08e39295a2594f463b962
    > Bug: chromium:1056170
    > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2467854
    > Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
    > Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
    > Reviewed-by: Omer Katz <omerkatz@chromium.org>
    > Cr-Commit-Position: refs/heads/master@{#70567}
    
    TBR=ulan@chromium.org,mlippautz@chromium.org,bikineev@chromium.org,omerkatz@chromium.org
    
    Change-Id: I64a2cf2259bdaed81f6e0f92bdcc7a1f0df4d197
    No-Presubmit: true
    No-Tree-Checks: true
    No-Try: true
    Bug: chromium:1056170
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2479471Reviewed-by: 's avatarMaya Lekova <mslekova@chromium.org>
    Commit-Queue: Maya Lekova <mslekova@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#70571}
    fba14bde
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