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Martin Kustermann 34763bc4c9 Reland "[VM] Introduction of type testing stubs - Part 1-4"

Relands 165c583d57

    [VM] Introduction of type testing stubs - Part 1

    This CL:

      * Adds a field to [RawAbstractType] which will always hold a pointer
        to the entrypoint of a type testing stub

      * Makes this new field be initialized to a default stub whenever a
        instances are created (e.g. via Type::New(), snapshot reader, ...)

      * Makes the clustered snapshotter write a reference to the
        corresponding [RawInstructions] object when writing the field and do
        the reverse when reading it.

      * Makes us call the type testing stub for performing assert-assignable
        checks.

    To reduce unnecessary loads on callsites, we store the entrypoint of the
    type testing stubs directly in the type objects.  This means that the
    caller of type testing stubs can simply branch there without populating
    a code object first.  This also means that the type testing stubs
    themselves have no access to a pool and we therefore also don't hold on
    to the [Code] object, only the [Instruction] object is necessary.

    The type testing stubs do not setup a frame themselves and also have no
    safepoint.  In the case when the type testing stubs could not determine
    a positive answer they will tail-call a general-purpose stub.

    The general-purpose stub sets up a stub frame, tries to consult a
    [SubtypeTestCache] and bails out to runtime if this was unsuccessful.

    This CL is just the the first, for ease of reviewing.  The actual
    type-specialized type testing stubs will be generated in later CLs.

    Reviewed-on: https://dart-review.googlesource.com/44787

Relands f226c22424

    [VM] Introduction of type testing stubs - Part 2

    This CL starts building type testing stubs specialzed for [Type] objects
    we test against.

    More specifically, it adds support for:

      * Handling obvious fast cases on the call sites (while still having a
        call to stub for negative case)

      * Handling type tests against type parameters, by loading the value
        of the type parameter on the call sites and invoking it's type testing stub.

      * Specialzed type testing stubs for instantiated types where we can
        do [CidRange]-based subtype-checks.

        ==> e.g. String/List<dynamic>

      * Specialzed type testing stubs for instantiated types where we can
        do [CidRange]-based subclass-checks for the class and
        [CidRange]-based subtype-checks for the type arguments.

        ==> e.g. Widget<State>, where we know [Widget] is only extended and not
                 implemented.

      * Specialzed type testing stubs for certain non-instantiated types where we
        can do [CidRange]-based subclass-checks for the class and
        [CidRange]-based subtype-checks for the instantiated type arguments and
        cid based comparisons for type parameters.  (Note that this fast-case migth
        result in some false-negatives!)

        ==> e.g. _HashMapEntry<K, V>, where we know [_HashMapEntry] is only
                 extended and not implemented.

       This optimizes cases where the caller uses `new HashMap<A, B>()` and only
       uses `A` and `B` as key/values (and not subclasses of it).  The false-negative
       can occur when subtypes of A or B are used.  In such cases we fall back to the
       [SubtypeTestCache]-based imlementation.

    Reviewed-on: https://dart-review.googlesource.com/44788

Relands 25f98bcc75

    [VM] Introduction of type testing stubs - Part 3

    The changes include:

      * Make AssertAssignableInstr no longer have a call-summary, which
        helps methods with several parameter checks by not having to
        re-load/re-initialize type arguments registers

      * Lazily create SubtypeTestCaches: We already go to runtime to warm up
        the caches, so we now also create the caches on the first runtime
        call and patch the pool entries.

      * No longer load the destination name into a register: We only need
        the name when we throw an exception, so it is not on the hot path.
        Instead we let the runtime look at the call site, decoding a pool
        index from the instructions stream.  The destination name will be
        available in the pool, at a consecutive index to the subtype cache.

      * Remove the fall-through to N=1 case for probing subtypeing tests,
        since those will always be handled by the optimized stubs.

      * Do not generate optimized stubs for FutureOr<T> (so far it just
        falled-through to TTS).  We can make optimzed version of that later,
        but it requires special subtyping rules.

      * Local code quality improvement in the type-testing-stubs: Avoid
        extra jump at last case of cid-class-range checks.

    There are still a number of optimization opportunities we can do in
    future changes.

    Reviewed-on: https://dart-review.googlesource.com/46984

Relands 2c52480ec8

    [VM] Introduction of type testing stubs - Part 4

    In order to avoid generating type testing stubs for too many types in
    the system - and thereby potentially cause an increase in code size -
    this change introduces a smarter way to decide for which types we should
    generate optimized type testing stubs.

    The precompiler creates a [TypeUsageInfo] which we use to collect
    information.  More specifically:

       a) We collect the destination types for all type checks we emit
          (we do this inside AssertAssignableInstr::EmitNativeCode).

          -> These are types we might want to generate optimized type testing
             stubs for.

       b) We collect type argument vectors used in instance creations (we do
          this inside AllocateObjectInstr::EmitNativeCode) and keep a set of
          of used type argument vectors for each class.

    After the precompiler has finished compiling normal code we scan the set
    of destination types collected in a) for uninstantiated types (or more
    specifically, type parameter types).

    We then propagate the type argument vectors used on object allocation sites,
    which were collected in b), in order to find out what kind of types are flowing
    into those type parameters.

    This allows us to extend the set of types which we test against, by
    adding the types that flow into type parameters.

    We use this final augmented set of destination types as a "filter" when
    making the decision whether to generate an optimized type testing stub
    for a given type.

    Reviewed-on: https://dart-review.googlesource.com/48640

Issue https://github.com/dart-lang/sdk/issues/32603

Change-Id: I6d33d4ca3d5187a1eb1664078c003061855f0160
Reviewed-on: https://dart-review.googlesource.com/50482
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>