C++ ExpressionPtr::isReferencedValid方法代码示例

/*
  The classical use/def isnt quite enough here. There are two unusual
  issues:
   - the ref/non-ref issue.
     An assignment to a var which is referenced doesnt end its
     lifetime. In fact it could just be a "use" of the var. But it
     also counts as a def.
   - the destructor issue.
     variables which might need to be destroyed later are technically
     alive, but dont interfere with any other variables in the same state.
     They /do/ interfere with any truly "live" variables, however.
     These are "dying".

   So we end up defining, use, kill, def and dying.

  use : a read of the variable, an ordinary assignment if it could
        be referenced

  kill : an unset, a ref assignment, or, for non referenced vars, any assignment

  def : ref or normal assignment

  dying : a variable whose destructor is (partially/locally) anticipated.
*/
void LiveDict::updateAccess(ExpressionPtr e) {
  int cls = e->getExprClass();
  if (cls & Expression::Store) {
    /*
      Handled when we see the lhs
    */
    return;
  }

  int eid = e->getCanonID();
  int context = e->getContext();
  bool unset = false;
  bool store = false;
  if (context & Expression::LValue && context & Expression::UnsetContext) {
    unset = true;
  } else if (context & Expression::AssignmentLHS) {
    store = true;
  }

  if (e->is(Expression::KindOfSimpleVariable)) {
    SimpleVariablePtr sv(static_pointer_cast<SimpleVariable>(e));
    bool use = false, kill = false, def = false;
    Symbol *sym = sv->getSymbol();
    bool isReferenced =
      e->isReferencedValid() ?
        e->isReferenced() :
        sym && sym->isReferenced();
    bool isNeeded =
      e->isNeededValid() ?
        e->isNeeded() :
        sym && sym->isNeeded();
    if (unset) {
      kill = true;
    } else if (store) {
      if (context & Expression::RefAssignmentLHS ||
          (!m_am.hasWildRefs() && !isReferenced)) {
        kill = true;
      }
      def = true;
    } else if ((context & Expression::Declaration) == Expression::Declaration) {
      // a global declaration
      def = kill = true;
    } else if (context & (Expression::LValue|
                          Expression::RefValue|
                          Expression::DeepReference|
                          Expression::UnsetContext|
                          Expression::OprLValue)) {
      use = def = true;
    } else {
      use = true;
    }
    if (kill && (!sym || isNeeded || isReferenced) &&
        !BitOps::get_bit(eid, m_altered) &&
        !BitOps::get_bit(eid, m_available)) {
      BitOps::set_bit(eid, m_dying, true);
    }
    if (use &&
        !BitOps::get_bit(eid, m_altered) &&
        !BitOps::get_bit(eid, m_available)) {
      BitOps::set_bit(eid, m_anticipated, true);
      e->setAnticipated();
    }
    if (kill) {
      BitOps::set_bit(eid, m_altered, true);
      BitOps::set_bit(eid, m_available, def);
    } else if (def) {
      BitOps::set_bit(eid, m_available, true);
    }

    if (!m_am.couldBeAliased(sv)) {
      return;
    }
  } else if (!e->is(Expression::KindOfDynamicVariable) &&
             (unset || (context & Expression::RefAssignmentLHS))) {
    // An unset, or a reference assignment to anything other
    // than a simple or dynamic variable can never affect a simple
//.........这里部分代码省略.........

//.........这里部分代码省略.........
            isRhsNeeded = Expression::CheckNeededRHS(rhs);
          }
        }
        break;
      default:
        break;
    }
  }

  bool isLhsSimpleVar = false;
  bool isLhsDynamic   = false;
  bool isRefd         = false;
  if (lhs) {
    isLhsSimpleVar = lhs->is(Expression::KindOfSimpleVariable);

    // TODO: can a variable only be simple or dynamic?
    // If so, this is un-necessary
    isLhsDynamic   = lhs->is(Expression::KindOfDynamicVariable);

    if (isLhsSimpleVar) {
      // clean up the LHS AST
      lhs->clearAvailable();
      lhs->clearNeeded();
      lhs->clearNeededValid();

      if (BitOps::get_bit(lhs->getCanonID(), m_obj)) {
        lhs->setNeeded();
        lhs->setNeededValid();
      } else if (!BitOps::get_bit(lhs->getCanonID(), m_noobj)) {
        lhs->setAvailable();
      }
    }

    if (lhs->isReferencedValid() && lhs->isReferenced() && isRhsNeeded) {
      // could we possibly have modified another referenced variable?
      isRefd = true;
    }

    if (isLhsSimpleVar && isRhsNeeded) {
      // we see this case:
      // $x = new ...
      // so we mark $x as being needed
      BitOps::set_bit(lhs->getCanonID(), m_obj, true);
      BitOps::set_bit(lhs->getCanonID(), m_noobj, false);
    } else if (isLhsSimpleVar && canKill && !isRhsNeeded) {
      // we saw an assignment that was of the form
      // $x = <primitive>
      // we can now set $x to be not an object
      BitOps::set_bit(lhs->getCanonID(), m_obj, false);
      BitOps::set_bit(lhs->getCanonID(), m_noobj, true);
    }
  }

  if (isLhsDynamic && isRhsNeeded) {
    // in this case, we must set EVERY variable to contain an object
    BitOps::set(size(), m_obj, -1 /* true for each bit */);
    BitOps::set(size(), m_noobj, 0 /* false for each bit */);

    // we're done, since it can be no worse (no more conservative) than this
    return;
  }

  // do we see a load which could cause the value of this expr to be changed?
  // for example:
  // function foo(&$x) { $x = 10; }
  // $x = 30;