bool run()
 {
     ASSERT(m_graph.m_form == ThreadedCPS);
     ASSERT(m_graph.m_unificationState == LocallyUnified);
     
     // Ensure that all Phi functions are unified.
     for (BlockIndex blockIndex = m_graph.m_blocks.size(); blockIndex--;) {
         BasicBlock* block = m_graph.m_blocks[blockIndex].get();
         if (!block)
             continue;
         ASSERT(block->isReachable);
         
         for (unsigned phiIndex = block->phis.size(); phiIndex--;) {
             Node* phi = block->phis[phiIndex];
             for (unsigned childIdx = 0; childIdx < AdjacencyList::Size; ++childIdx) {
                 if (!phi->children.child(childIdx))
                     break;
                 
                 phi->variableAccessData()->unify(
                     phi->children.child(childIdx)->variableAccessData());
             }
         }
     }
     
     // Ensure that all predictions are fixed up based on the unification.
     for (unsigned i = 0; i < m_graph.m_variableAccessData.size(); ++i) {
         VariableAccessData* data = &m_graph.m_variableAccessData[i];
         data->find()->predict(data->nonUnifiedPrediction());
         data->find()->mergeIsCaptured(data->isCaptured());
         data->find()->mergeStructureCheckHoistingFailed(data->structureCheckHoistingFailed());
         data->find()->mergeShouldNeverUnbox(data->shouldNeverUnbox());
         data->find()->mergeIsLoadedFrom(data->isLoadedFrom());
     }
     
     m_graph.m_unificationState = GloballyUnified;
     return true;
 }
    void propagate(Node* node)
    {
        NodeFlags flags = node->flags() & NodeBytecodeBackPropMask;

        switch (node->op()) {
        case GetLocal: {
            VariableAccessData* variableAccessData = node->variableAccessData();
            flags &= ~NodeBytecodeUsesAsInt; // We don't care about cross-block uses-as-int.
            m_changed |= variableAccessData->mergeFlags(flags);
            break;
        }

        case SetLocal: {
            VariableAccessData* variableAccessData = node->variableAccessData();
            if (!variableAccessData->isLoadedFrom())
                break;
            flags = variableAccessData->flags();
            RELEASE_ASSERT(!(flags & ~NodeBytecodeBackPropMask));
            flags |= NodeBytecodeUsesAsNumber; // Account for the fact that control flow may cause overflows that our modeling can't handle.
            node->child1()->mergeFlags(flags);
            break;
        }

        case Flush: {
            VariableAccessData* variableAccessData = node->variableAccessData();
            m_changed |= variableAccessData->mergeFlags(NodeBytecodeUsesAsValue);
            break;
        }

        case MovHint:
        case Check:
            break;

        case BitAnd:
        case BitOr:
        case BitXor:
        case BitRShift:
        case BitLShift:
        case BitURShift:
        case ArithIMul: {
            flags |= NodeBytecodeUsesAsInt;
            flags &= ~(NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero | NodeBytecodeUsesAsOther);
            flags &= ~NodeBytecodeUsesAsArrayIndex;
            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }

        case StringCharCodeAt: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            node->child2()->mergeFlags(NodeBytecodeUsesAsValue | NodeBytecodeUsesAsInt | NodeBytecodeUsesAsArrayIndex);
            break;
        }

        case UInt32ToNumber: {
            node->child1()->mergeFlags(flags);
            break;
        }

        case ValueAdd: {
            if (isNotNegZero(node->child1().node()) || isNotNegZero(node->child2().node()))
                flags &= ~NodeBytecodeNeedsNegZero;
            if (node->child1()->hasNumberResult() || node->child2()->hasNumberResult())
                flags &= ~NodeBytecodeUsesAsOther;
            if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
                flags |= NodeBytecodeUsesAsNumber;
            if (!m_allowNestedOverflowingAdditions)
                flags |= NodeBytecodeUsesAsNumber;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }

        case ArithAdd: {
            flags &= ~NodeBytecodeUsesAsOther;
            if (isNotNegZero(node->child1().node()) || isNotNegZero(node->child2().node()))
                flags &= ~NodeBytecodeNeedsNegZero;
            if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
                flags |= NodeBytecodeUsesAsNumber;
            if (!m_allowNestedOverflowingAdditions)
                flags |= NodeBytecodeUsesAsNumber;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }

        case ArithClz32: {
            flags &= ~(NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero | NodeBytecodeUsesAsOther | ~NodeBytecodeUsesAsArrayIndex);
            flags |= NodeBytecodeUsesAsInt;
            node->child1()->mergeFlags(flags);
            break;
        }

        case ArithSub: {
            flags &= ~NodeBytecodeUsesAsOther;
            if (isNotNegZero(node->child1().node()) || isNotPosZero(node->child2().node()))
                flags &= ~NodeBytecodeNeedsNegZero;
            if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
                flags |= NodeBytecodeUsesAsNumber;
            if (!m_allowNestedOverflowingAdditions)
                flags |= NodeBytecodeUsesAsNumber;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }

        case ArithNegate: {
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            break;
        }

        case ArithMul: {
            // As soon as a multiply happens, we can easily end up in the part
            // of the double domain where the point at which you do truncation
            // can change the outcome. So, ArithMul always forces its inputs to
            // check for overflow. Additionally, it will have to check for overflow
            // itself unless we can prove that there is no way for the values
            // produced to cause double rounding.

            if (!isWithinPowerOfTwo<22>(node->child1().node())
                && !isWithinPowerOfTwo<22>(node->child2().node()))
                flags |= NodeBytecodeUsesAsNumber;

            node->mergeFlags(flags);

            flags |= NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero;
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }

        case ArithDiv: {
            flags |= NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero;
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }

        case ArithMod: {
            flags |= NodeBytecodeUsesAsNumber;
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags & ~NodeBytecodeNeedsNegZero);
            break;
        }

        case GetByVal: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            node->child2()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther | NodeBytecodeUsesAsInt | NodeBytecodeUsesAsArrayIndex);
            break;
        }

        case NewArrayWithSize: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue | NodeBytecodeUsesAsInt | NodeBytecodeUsesAsArrayIndex);
            break;
        }

        case NewTypedArray: {
            // Negative zero is not observable. NaN versus undefined are only observable
            // in that you would get a different exception message. So, like, whatever: we
            // claim here that NaN v. undefined is observable.
            node->child1()->mergeFlags(NodeBytecodeUsesAsInt | NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther | NodeBytecodeUsesAsArrayIndex);
            break;
        }

        case StringCharAt: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            node->child2()->mergeFlags(NodeBytecodeUsesAsValue | NodeBytecodeUsesAsInt | NodeBytecodeUsesAsArrayIndex);
            break;
        }

        case ToString:
        case CallStringConstructor: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther);
            break;
        }

        case ToPrimitive:
        case ToNumber: {
            node->child1()->mergeFlags(flags);
            break;
        }

        case PutByValDirect:
        case PutByVal: {
            m_graph.varArgChild(node, 0)->mergeFlags(NodeBytecodeUsesAsValue);
            m_graph.varArgChild(node, 1)->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther | NodeBytecodeUsesAsInt | NodeBytecodeUsesAsArrayIndex);
            m_graph.varArgChild(node, 2)->mergeFlags(NodeBytecodeUsesAsValue);
            break;
        }

        case Switch: {
            SwitchData* data = node->switchData();
            switch (data->kind) {
            case SwitchImm:
                // We don't need NodeBytecodeNeedsNegZero because if the cases are all integers
                // then -0 and 0 are treated the same.  We don't need NodeBytecodeUsesAsOther
                // because if all of the cases are integers then NaN and undefined are
                // treated the same (i.e. they will take default).
                node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsInt);
                break;
            case SwitchChar: {
                // We don't need NodeBytecodeNeedsNegZero because if the cases are all strings
                // then -0 and 0 are treated the same.  We don't need NodeBytecodeUsesAsOther
                // because if all of the cases are single-character strings then NaN
                // and undefined are treated the same (i.e. they will take default).
                node->child1()->mergeFlags(NodeBytecodeUsesAsNumber);
                break;
            }
            case SwitchString:
                // We don't need NodeBytecodeNeedsNegZero because if the cases are all strings
                // then -0 and 0 are treated the same.
                node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther);
                break;
            case SwitchCell:
                // There is currently no point to being clever here since this is used for switching
                // on objects.
                mergeDefaultFlags(node);
                break;
            }
            break;
        }

        case Identity:
            // This would be trivial to handle but we just assert that we cannot see these yet.
            RELEASE_ASSERT_NOT_REACHED();
            break;

        // Note: ArithSqrt, ArithUnary and other math intrinsics don't have special
        // rules in here because they are always followed by Phantoms to signify that if the
        // method call speculation fails, the bytecode may use the arguments in arbitrary ways.
        // This corresponds to that possibility of someone doing something like:
        // Math.sin = function(x) { doArbitraryThingsTo(x); }

        default:
            mergeDefaultFlags(node);
            break;
        }
    }
    void propagate(Node* node)
    {
        NodeFlags flags = node->flags() & NodeBytecodeBackPropMask;
        
        switch (node->op()) {
        case GetLocal: {
            VariableAccessData* variableAccessData = node->variableAccessData();
            variableAccessData->mergeFlags(flags);
            break;
        }
            
        case SetLocal: {
            VariableAccessData* variableAccessData = node->variableAccessData();
            if (!variableAccessData->isLoadedFrom())
                break;
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            break;
        }
            
        case BitAnd:
        case BitOr:
        case BitXor:
        case BitRShift:
        case BitLShift:
        case BitURShift:
        case ArithIMul: {
            flags |= NodeBytecodeUsesAsInt;
            flags &= ~(NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero | NodeBytecodeUsesAsOther);
            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }
            
        case ValueToInt32: {
            flags |= NodeBytecodeUsesAsInt;
            flags &= ~(NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero | NodeBytecodeUsesAsOther);
            node->child1()->mergeFlags(flags);
            break;
        }
            
        case StringCharCodeAt: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            node->child2()->mergeFlags(NodeBytecodeUsesAsValue | NodeBytecodeUsesAsInt);
            break;
        }
            
        case Identity: 
        case UInt32ToNumber: {
            node->child1()->mergeFlags(flags);
            break;
        }

        case ValueAdd: {
            if (isNotNegZero(node->child1().node()) || isNotNegZero(node->child2().node()))
                flags &= ~NodeBytecodeNeedsNegZero;
            if (node->child1()->hasNumberResult() || node->child2()->hasNumberResult())
                flags &= ~NodeBytecodeUsesAsOther;
            if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
                flags |= NodeBytecodeUsesAsNumber;
            if (!m_allowNestedOverflowingAdditions)
                flags |= NodeBytecodeUsesAsNumber;
            
            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }
            
        case ArithAdd: {
            if (isNotNegZero(node->child1().node()) || isNotNegZero(node->child2().node()))
                flags &= ~NodeBytecodeNeedsNegZero;
            if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
                flags |= NodeBytecodeUsesAsNumber;
            if (!m_allowNestedOverflowingAdditions)
                flags |= NodeBytecodeUsesAsNumber;
            
            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }
            
        case ArithSub: {
            if (isNotNegZero(node->child1().node()) || isNotPosZero(node->child2().node()))
                flags &= ~NodeBytecodeNeedsNegZero;
            if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
                flags |= NodeBytecodeUsesAsNumber;
            if (!m_allowNestedOverflowingAdditions)
                flags |= NodeBytecodeUsesAsNumber;
            
            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }
            
        case ArithNegate: {
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            break;
        }
            
        case ArithMul: {
            // As soon as a multiply happens, we can easily end up in the part
            // of the double domain where the point at which you do truncation
            // can change the outcome. So, ArithMul always forces its inputs to
            // check for overflow. Additionally, it will have to check for overflow
            // itself unless we can prove that there is no way for the values
            // produced to cause double rounding.
            
            if (!isWithinPowerOfTwo<22>(node->child1().node())
                && !isWithinPowerOfTwo<22>(node->child2().node()))
                flags |= NodeBytecodeUsesAsNumber;
            
            node->mergeFlags(flags);
            
            flags |= NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero;
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }
            
        case ArithDiv: {
            flags |= NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero;
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }
            
        case ArithMod: {
            flags |= NodeBytecodeUsesAsNumber | NodeBytecodeNeedsNegZero;
            flags &= ~NodeBytecodeUsesAsOther;

            node->child1()->mergeFlags(flags);
            node->child2()->mergeFlags(flags);
            break;
        }
            
        case GetByVal: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            node->child2()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther | NodeBytecodeUsesAsInt);
            break;
        }
            
        case GetMyArgumentByValSafe: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther | NodeBytecodeUsesAsInt);
            break;
        }
            
        case NewArrayWithSize: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue | NodeBytecodeUsesAsInt);
            break;
        }
            
        case NewTypedArray: {
            // Negative zero is not observable. NaN versus undefined are only observable
            // in that you would get a different exception message. So, like, whatever: we
            // claim here that NaN v. undefined is observable.
            node->child1()->mergeFlags(NodeBytecodeUsesAsInt | NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther);
            break;
        }
            
        case StringCharAt: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            node->child2()->mergeFlags(NodeBytecodeUsesAsValue | NodeBytecodeUsesAsInt);
            break;
        }
            
        case ToString: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther);
            break;
        }
            
        case ToPrimitive: {
            node->child1()->mergeFlags(flags);
            break;
        }
            
        case PutByVal: {
            m_graph.varArgChild(node, 0)->mergeFlags(NodeBytecodeUsesAsValue);
            m_graph.varArgChild(node, 1)->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther | NodeBytecodeUsesAsInt);
            m_graph.varArgChild(node, 2)->mergeFlags(NodeBytecodeUsesAsValue);
            break;
        }
            
        case Switch: {
            SwitchData* data = node->switchData();
            switch (data->kind) {
            case SwitchImm:
                // We don't need NodeBytecodeNeedsNegZero because if the cases are all integers
                // then -0 and 0 are treated the same.  We don't need NodeBytecodeUsesAsOther
                // because if all of the cases are integers then NaN and undefined are
                // treated the same (i.e. they will take default).
                node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsInt);
                break;
            case SwitchChar: {
                // We don't need NodeBytecodeNeedsNegZero because if the cases are all strings
                // then -0 and 0 are treated the same.  We don't need NodeBytecodeUsesAsOther
                // because if all of the cases are single-character strings then NaN
                // and undefined are treated the same (i.e. they will take default).
                node->child1()->mergeFlags(NodeBytecodeUsesAsNumber);
                break;
            }
            case SwitchString:
                // We don't need NodeBytecodeNeedsNegZero because if the cases are all strings
                // then -0 and 0 are treated the same.
                node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther);
                break;
            }
            break;
        }
            
        default:
            mergeDefaultFlags(node);
            break;
        }
    }