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    • Benedikt Meurer's avatar
      [builtins] Refactor the promise resolution and rejection logic. · c0412961
      Benedikt Meurer authored
      This introduces dedicated builtins
      
        - FulfillPromise,
        - RejectPromise, and
        - ResolvePromise,
      
      which perform the corresponding operations from the language
      specification, and removes the redundant entry points and the
      excessive inlining of these operations into other builtins. We
      also add the same logic on the C++ side, so that we don't need
      to go into JavaScript land when resolving/rejecting from the
      API.
      
      The C++ side has a complete implementation, including full support
      for the debugger and the current PromiseHook machinery. This is to
      avoid constantly crossing the boundary for those cases, and to also
      simplify the CSA side (and soon the TurboFan side), where we only
      do the fast-path and bail out to the runtime for the general handling.
      
      On top of this we introduce %_RejectPromise and %_ResolvePromise,
      which are entry points used by the bytecode and parser desugarings
      for async functions, and also used by the V8 Extras API. Thanks to
      this we can uniformly optimize these in TurboFan, where we have
      corresponding operators JSRejectPromise and JSResolvePromise, which
      currently just call into the builtins, but middle-term can be further
      optimized, i.e. to skip the "then" lookup for JSResolvePromise when
      we know something about the resolution.
      
      In TurboFan we can also already inline the default PromiseCapability
      [[Reject]] and [[Resolve]] functions, although this is not as effective
      as it can be right now, until we have inlining support for the Promise
      constructor (being worked on by petermarshall@ right now) and/or SFI
      based CALL_IC feedback.
      
      Overall this change is meant as a refactoring without significant
      performance impact anywhere; it seems to improve performance of
      simple async functions a bit, but otherwise is neutral.
      
      Bug: v8:7253
      Change-Id: Id0b979f9b2843560e38cd8df4b02627dad4b6d8c
      Reviewed-on: https://chromium-review.googlesource.com/911632Reviewed-by: 's avatarSathya Gunasekaran <gsathya@chromium.org>
      Reviewed-by: 's avatarBenedikt Meurer <bmeurer@chromium.org>
      Reviewed-by: 's avatarGeorg Neis <neis@chromium.org>
      Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
      Cr-Commit-Position: refs/heads/master@{#51260}
      c0412961