C++ TypeConstraint::wantArrayShape方法代码示例

bool typeFitsConstraint(Type t, TypeConstraint tc) {
  switch (tc.category) {
    case DataTypeGeneric:
      return true;

    case DataTypeCountness:
      // Consumers using this constraint expect the type to be relaxed to
      // Uncounted or left alone, so something like Arr|Obj isn't specific
      // enough.
      return !t.maybe(TCounted) ||
             t.subtypeOfAny(TStr, TArr, TObj,
                            TRes, TBoxedCell);

    case DataTypeCountnessInit:
      return typeFitsConstraint(t, DataTypeCountness) &&
             (t <= TUninit || !t.maybe(TUninit));

    case DataTypeSpecific:
      return t.isKnownDataType();

    case DataTypeSpecialized:
      // Type::isSpecialized() returns true for types like {Arr<Packed>|Int}
      // and Arr has non-specialized subtypes, so we require that t is
      // specialized, a strict subtype of Obj or Arr, and that it fits the
      // specific requirements of tc.

      assertx(tc.wantClass() ^ tc.wantArrayKind());

      if (t < TObj && t.clsSpec()) {
        return tc.wantClass() &&
               t.clsSpec().cls()->classof(tc.desiredClass());
      }
      if (t < TArr && t.arrSpec()) {
        auto arrSpec = t.arrSpec();
        if (tc.wantArrayShape() && !arrSpec.shape()) return false;
        if (tc.wantArrayKind() && !arrSpec.kind()) return false;
        return true;
      }

      return false;
  }

  not_reached();
}

/*
 * Return a copy of tc refined with any new information in newTc.
 */
TypeConstraint applyConstraint(TypeConstraint tc, const TypeConstraint newTc) {
  tc.category = std::max(newTc.category, tc.category);

  if (newTc.wantArrayKind()) tc.setWantArrayKind();
  if (newTc.wantArrayShape()) tc.setWantArrayShape();

  if (newTc.wantClass()) {
    if (tc.wantClass()) {
      // It only makes sense to constrain tc with a class that's related to its
      // existing class, and we want to preserve the more derived of the two.
      auto cls1 = tc.desiredClass();
      auto cls2 = newTc.desiredClass();
      tc.setDesiredClass(cls1->classof(cls2) ? cls1 : cls2);
    } else {
      tc.setDesiredClass(newTc.desiredClass());
    }
  }

  return tc;
}

/*
 * relaxConstraint returns the least specific TypeConstraint 'tc' that doesn't
 * prevent the intersection of knownType and relaxType(toRelax, tc) from
 * satisfying origTc. It is used in IRBuilder::constrainValue and
 * IRBuilder::constrainStack to determine how to constrain the typeParam and
 * src values of CheckType/CheckStk instructions, and the src values of
 * AssertType/AssertStk instructions.
 *
 * AssertType example:
 * t24:Obj<C> = AssertType<{Obj<C>|InitNull}> t4:Obj
 *
 * If constrainValue is called with (t24, DataTypeSpecialized), relaxConstraint
 * will be called with (DataTypeSpecialized, Obj<C>|InitNull, Obj). After a few
 * iterations it will determine that constraining Obj with DataTypeCountness
 * will still allow the result type of the AssertType instruction to satisfy
 * DataTypeSpecialized, because relaxType(Obj, DataTypeCountness) == Obj.
 */
TypeConstraint relaxConstraint(const TypeConstraint origTc,
                               const Type knownType, const Type toRelax) {
  ITRACE(4, "relaxConstraint({}, knownType = {}, toRelax = {})\n",
         origTc, knownType, toRelax);
  Trace::Indent _i;

  auto const dstType = knownType & toRelax;
  always_assert_flog(typeFitsConstraint(dstType, origTc),
                     "refine({}, {}) doesn't fit {}",
                     knownType, toRelax, origTc);

  // Preserve origTc's weak property.
  TypeConstraint newTc{DataTypeGeneric};
  newTc.weak = origTc.weak;

  while (true) {
    if (newTc.isSpecialized()) {
      // We need to ask for the right kind of specialization, so grab it from
      // origTc.
      if (origTc.wantArrayKind()) newTc.setWantArrayKind();
      if (origTc.wantArrayShape()) newTc.setWantArrayShape();
      if (origTc.wantClass()) newTc.setDesiredClass(origTc.desiredClass());
    }

    auto const relaxed = relaxType(toRelax, newTc);
    auto const newDstType = relaxed & knownType;
    if (typeFitsConstraint(newDstType, origTc)) break;

    ITRACE(5, "newDstType = {}, newTc = {}; incrementing constraint\n",
      newDstType, newTc);
    incCategory(newTc.category);
  }

  ITRACE(4, "Returning {}\n", newTc);
  // newTc shouldn't be any more specific than origTc.
  always_assert(newTc.category <= origTc.category);
  return newTc;
}