[apple/javascriptcore.git] / dfg / DFGBackwardsPropagationPhase.cpp

/*
 * Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#include "config.h"
#include "DFGBackwardsPropagationPhase.h"

#if ENABLE(DFG_JIT)

#include "DFGBasicBlockInlines.h"
#include "DFGGraph.h"
#include "DFGPhase.h"
#include "JSCInlines.h"

namespace JSC { namespace DFG {

class BackwardsPropagationPhase : public Phase {
public:
    BackwardsPropagationPhase(Graph& graph)
        : Phase(graph, "backwards propagation")
    {
    }
    
    bool run()
    {
        m_changed = true;
        while (m_changed) {
            m_changed = false;
            for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
                BasicBlock* block = m_graph.block(blockIndex);
                if (!block)
                    continue;
            
                // Prevent a tower of overflowing additions from creating a value that is out of the
                // safe 2^48 range.
                m_allowNestedOverflowingAdditions = block->size() < (1 << 16);
            
                for (unsigned indexInBlock = block->size(); indexInBlock--;)
                    propagate(block->at(indexInBlock));
            }
        }
        
        return true;
    }

private:
    bool isNotNegZero(Node* node)
    {
        if (!m_graph.isNumberConstant(node))
            return false;
        double value = m_graph.valueOfNumberConstant(node);
        return (value || 1.0 / value > 0.0);
    }
    
    bool isNotPosZero(Node* node)
    {
        if (!m_graph.isNumberConstant(node))
            return false;
        double value = m_graph.valueOfNumberConstant(node);
        return (value || 1.0 / value < 0.0);
    }

    // Tests if the absolute value is strictly less than the power of two.
    template<int power>
    bool isWithinPowerOfTwoForConstant(Node* node)
    {
        JSValue immediateValue = node->valueOfJSConstant(codeBlock());
        if (!immediateValue.isNumber())
            return false;
        double immediate = immediateValue.asNumber();
        return immediate > -(static_cast<int64_t>(1) << power) && immediate < (static_cast<int64_t>(1) << power);
    }
    
    template<int power>
    bool isWithinPowerOfTwoNonRecursive(Node* node)
    {
        if (node->op() != JSConstant)
            return false;
        return isWithinPowerOfTwoForConstant<power>(node);
    }
    
    template<int power>
    bool isWithinPowerOfTwo(Node* node)
    {
        switch (node->op()) {
        case JSConstant: {
            return isWithinPowerOfTwoForConstant<power>(node);
        }
            
        case BitAnd: {
            if (power > 31)
                return true;
            
            return isWithinPowerOfTwoNonRecursive<power>(node->child1().node())
                || isWithinPowerOfTwoNonRecursive<power>(node->child2().node());
        }
            
        case BitOr:
        case BitXor:
        case BitLShift: {
            return power > 31;
        }
            
        case BitRShift:
        case BitURShift: {
            if (power > 31)
                return true;
            
            Node* shiftAmount = node->child2().node();
            if (shiftAmount->op() != JSConstant)
                return false;
            JSValue immediateValue = shiftAmount->valueOfJSConstant(codeBlock());
            if (!immediateValue.isInt32())
                return false;
            return immediateValue.asInt32() > 32 - power;
        }
            
        default:
            return false;
        }
    }

    template<int power>
    bool isWithinPowerOfTwo(Edge edge)
    {
        return isWithinPowerOfTwo<power>(edge.node());
    }

    bool mergeDefaultFlags(Node* node)
    {
        bool changed = false;
        if (node->flags() & NodeHasVarArgs) {
            for (unsigned childIdx = node->firstChild();
                childIdx < node->firstChild() + node->numChildren();
                childIdx++) {
                if (!!m_graph.m_varArgChildren[childIdx])
                    changed |= m_graph.m_varArgChildren[childIdx]->mergeFlags(NodeBytecodeUsesAsValue);
            }
        } else {
            if (!node->child1())
                return changed;
            changed |= node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
            if (!node->child2())
                return changed;
            changed |= node->child2()->mergeFlags(NodeBytecodeUsesAsValue);
            if (!node->child3())
                return changed;
            changed |= node->child3()->mergeFlags(NodeBytecodeUsesAsValue);
        }
        return changed;
    }
    
    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: {
            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 | NodeBytecodeUsesAsArrayIndex);
            break;
        }
            
        case GetMyArgumentByValSafe: {
            node->child1()->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: {
            node->child1()->mergeFlags(NodeBytecodeUsesAsNumber | NodeBytecodeUsesAsOther);
            break;
        }
            
        case ToPrimitive: {
            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;
            }
            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, ArithSin, and ArithCos 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;
        }
    }
    
    bool m_allowNestedOverflowingAdditions;
    bool m_changed;
};

bool performBackwardsPropagation(Graph& graph)
{
    SamplingRegion samplingRegion("DFG Backwards Propagation Phase");
    return runPhase<BackwardsPropagationPhase>(graph);
}

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)
Commit	Line	Data
93a37866	1	/*
81345200	2	* Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
93a37866 A	3	*
	4	* Redistribution and use in source and binary forms, with or without
	5	* modification, are permitted provided that the following conditions
	6	* are met:
	7	* 1. Redistributions of source code must retain the above copyright
	8	* notice, this list of conditions and the following disclaimer.
	9	* 2. Redistributions in binary form must reproduce the above copyright
	10	* notice, this list of conditions and the following disclaimer in the
	11	* documentation and/or other materials provided with the distribution.
	12	*
	13	* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
	14	* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	15	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	16	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
	17	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
	18	* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
	19	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	20	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	21	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	22	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	23	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	24	*/
	25
	26	#include "config.h"
	27	#include "DFGBackwardsPropagationPhase.h"
	28
	29	#if ENABLE(DFG_JIT)
	30
	31	#include "DFGBasicBlockInlines.h"
	32	#include "DFGGraph.h"
	33	#include "DFGPhase.h"
81345200	34	#include "JSCInlines.h"
93a37866 A	35
	36	namespace JSC { namespace DFG {
	37
	38	class BackwardsPropagationPhase : public Phase {
	39	public:
	40	BackwardsPropagationPhase(Graph& graph)
	41	: Phase(graph, "backwards propagation")
	42	{
	43	}
	44
	45	bool run()
	46	{
81345200 A	47	m_changed = true;
	48	while (m_changed) {
	49	m_changed = false;
	50	for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
	51	BasicBlock* block = m_graph.block(blockIndex);
	52	if (!block)
	53	continue;
	54
	55	// Prevent a tower of overflowing additions from creating a value that is out of the
	56	// safe 2^48 range.
	57	m_allowNestedOverflowingAdditions = block->size() < (1 << 16);
	58
	59	for (unsigned indexInBlock = block->size(); indexInBlock--;)
	60	propagate(block->at(indexInBlock));
	61	}
93a37866 A	62	}
	63
	64	return true;
	65	}
	66
	67	private:
	68	bool isNotNegZero(Node* node)
	69	{
	70	if (!m_graph.isNumberConstant(node))
	71	return false;
	72	double value = m_graph.valueOfNumberConstant(node);
	73	return (value \|\| 1.0 / value > 0.0);
	74	}
	75
	76	bool isNotPosZero(Node* node)
	77	{
	78	if (!m_graph.isNumberConstant(node))
	79	return false;
	80	double value = m_graph.valueOfNumberConstant(node);
	81	return (value \|\| 1.0 / value < 0.0);
	82	}
	83
	84	// Tests if the absolute value is strictly less than the power of two.
	85	template<int power>
	86	bool isWithinPowerOfTwoForConstant(Node* node)
	87	{
	88	JSValue immediateValue = node->valueOfJSConstant(codeBlock());
	89	if (!immediateValue.isNumber())
	90	return false;
	91	double immediate = immediateValue.asNumber();
	92	return immediate > -(static_cast<int64_t>(1) << power) && immediate < (static_cast<int64_t>(1) << power);
	93	}
	94
	95	template<int power>
	96	bool isWithinPowerOfTwoNonRecursive(Node* node)
	97	{
	98	if (node->op() != JSConstant)
	99	return false;
	100	return isWithinPowerOfTwoForConstant<power>(node);
	101	}
	102
	103	template<int power>
	104	bool isWithinPowerOfTwo(Node* node)
	105	{
	106	switch (node->op()) {
	107	case JSConstant: {
	108	return isWithinPowerOfTwoForConstant<power>(node);
	109	}
	110
	111	case BitAnd: {
	112	if (power > 31)
	113	return true;
	114
	115	return isWithinPowerOfTwoNonRecursive<power>(node->child1().node())
	116	\|\| isWithinPowerOfTwoNonRecursive<power>(node->child2().node());
	117	}
	118
	119	case BitOr:
	120	case BitXor:
81345200	121	case BitLShift: {
93a37866 A	122	return power > 31;
	123	}
	124
	125	case BitRShift:
	126	case BitURShift: {
	127	if (power > 31)
	128	return true;
	129
	130	Node* shiftAmount = node->child2().node();
	131	if (shiftAmount->op() != JSConstant)
	132	return false;
	133	JSValue immediateValue = shiftAmount->valueOfJSConstant(codeBlock());
	134	if (!immediateValue.isInt32())
	135	return false;
	136	return immediateValue.asInt32() > 32 - power;
	137	}
	138
	139	default:
	140	return false;
	141	}
	142	}
	143
	144	template<int power>
	145	bool isWithinPowerOfTwo(Edge edge)
	146	{
	147	return isWithinPowerOfTwo<power>(edge.node());
	148	}
	149
	150	bool mergeDefaultFlags(Node* node)
	151	{
	152	bool changed = false;
	153	if (node->flags() & NodeHasVarArgs) {
	154	for (unsigned childIdx = node->firstChild();
	155	childIdx < node->firstChild() + node->numChildren();
	156	childIdx++) {
	157	if (!!m_graph.m_varArgChildren[childIdx])
81345200	158	changed \|= m_graph.m_varArgChildren[childIdx]->mergeFlags(NodeBytecodeUsesAsValue);
93a37866 A	159	}
	160	} else {
	161	if (!node->child1())
	162	return changed;
81345200	163	changed \|= node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
93a37866 A	164	if (!node->child2())
93a37866 A	165	return changed;
81345200	166	changed \|= node->child2()->mergeFlags(NodeBytecodeUsesAsValue);
93a37866 A	167	if (!node->child3())
93a37866 A	168	return changed;
81345200	169	changed \|= node->child3()->mergeFlags(NodeBytecodeUsesAsValue);
93a37866 A	170	}
	171	return changed;
	172	}
	173
	174	void propagate(Node* node)
	175	{
81345200	176	NodeFlags flags = node->flags() & NodeBytecodeBackPropMask;
93a37866 A	177
	178	switch (node->op()) {
	179	case GetLocal: {
	180	VariableAccessData* variableAccessData = node->variableAccessData();
81345200 A	181	flags &= ~NodeBytecodeUsesAsInt; // We don't care about cross-block uses-as-int.
81345200 A	182	m_changed \|= variableAccessData->mergeFlags(flags);
93a37866 A	183	break;
	184	}
	185
	186	case SetLocal: {
	187	VariableAccessData* variableAccessData = node->variableAccessData();
	188	if (!variableAccessData->isLoadedFrom())
	189	break;
81345200 A	190	flags = variableAccessData->flags();
	191	RELEASE_ASSERT(!(flags & ~NodeBytecodeBackPropMask));
	192	flags \|= NodeBytecodeUsesAsNumber; // Account for the fact that control flow may cause overflows that our modeling can't handle.
	193	node->child1()->mergeFlags(flags);
	194	break;
	195	}
	196
	197	case Flush: {
	198	VariableAccessData* variableAccessData = node->variableAccessData();
	199	m_changed \|= variableAccessData->mergeFlags(NodeBytecodeUsesAsValue);
93a37866 A	200	break;
	201	}
	202
81345200 A	203	case MovHint:
	204	case Check:
	205	break;
	206
93a37866 A	207	case BitAnd:
	208	case BitOr:
	209	case BitXor:
	210	case BitRShift:
	211	case BitLShift:
	212	case BitURShift:
	213	case ArithIMul: {
81345200 A	214	flags \|= NodeBytecodeUsesAsInt;
	215	flags &= ~(NodeBytecodeUsesAsNumber \| NodeBytecodeNeedsNegZero \| NodeBytecodeUsesAsOther);
	216	flags &= ~NodeBytecodeUsesAsArrayIndex;
93a37866 A	217	node->child1()->mergeFlags(flags);
	218	node->child2()->mergeFlags(flags);
	219	break;
	220	}
	221
93a37866	222	case StringCharCodeAt: {
81345200 A	223	node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
81345200 A	224	node->child2()->mergeFlags(NodeBytecodeUsesAsValue \| NodeBytecodeUsesAsInt \| NodeBytecodeUsesAsArrayIndex);
93a37866 A	225	break;
	226	}
	227
93a37866 A	228	case UInt32ToNumber: {
	229	node->child1()->mergeFlags(flags);
	230	break;
	231	}
	232
	233	case ValueAdd: {
	234	if (isNotNegZero(node->child1().node()) \|\| isNotNegZero(node->child2().node()))
81345200	235	flags &= ~NodeBytecodeNeedsNegZero;
93a37866	236	if (node->child1()->hasNumberResult() \|\| node->child2()->hasNumberResult())
81345200	237	flags &= ~NodeBytecodeUsesAsOther;
93a37866	238	if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
81345200	239	flags \|= NodeBytecodeUsesAsNumber;
93a37866	240	if (!m_allowNestedOverflowingAdditions)
81345200	241	flags \|= NodeBytecodeUsesAsNumber;
93a37866 A	242
	243	node->child1()->mergeFlags(flags);
	244	node->child2()->mergeFlags(flags);
	245	break;
	246	}
	247
	248	case ArithAdd: {
	249	if (isNotNegZero(node->child1().node()) \|\| isNotNegZero(node->child2().node()))
81345200	250	flags &= ~NodeBytecodeNeedsNegZero;
93a37866	251	if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
81345200	252	flags \|= NodeBytecodeUsesAsNumber;
93a37866	253	if (!m_allowNestedOverflowingAdditions)
81345200	254	flags \|= NodeBytecodeUsesAsNumber;
93a37866 A	255
	256	node->child1()->mergeFlags(flags);
	257	node->child2()->mergeFlags(flags);
	258	break;
	259	}
	260
	261	case ArithSub: {
	262	if (isNotNegZero(node->child1().node()) \|\| isNotPosZero(node->child2().node()))
81345200	263	flags &= ~NodeBytecodeNeedsNegZero;
93a37866	264	if (!isWithinPowerOfTwo<32>(node->child1()) && !isWithinPowerOfTwo<32>(node->child2()))
81345200	265	flags \|= NodeBytecodeUsesAsNumber;
93a37866	266	if (!m_allowNestedOverflowingAdditions)
81345200	267	flags \|= NodeBytecodeUsesAsNumber;
93a37866 A	268
	269	node->child1()->mergeFlags(flags);
	270	node->child2()->mergeFlags(flags);
	271	break;
	272	}
	273
	274	case ArithNegate: {
81345200	275	flags &= ~NodeBytecodeUsesAsOther;
93a37866 A	276
	277	node->child1()->mergeFlags(flags);
	278	break;
	279	}
	280
	281	case ArithMul: {
	282	// As soon as a multiply happens, we can easily end up in the part
	283	// of the double domain where the point at which you do truncation
	284	// can change the outcome. So, ArithMul always forces its inputs to
	285	// check for overflow. Additionally, it will have to check for overflow
	286	// itself unless we can prove that there is no way for the values
	287	// produced to cause double rounding.
	288
	289	if (!isWithinPowerOfTwo<22>(node->child1().node())
	290	&& !isWithinPowerOfTwo<22>(node->child2().node()))
81345200	291	flags \|= NodeBytecodeUsesAsNumber;
93a37866 A	292
	293	node->mergeFlags(flags);
	294
81345200 A	295	flags \|= NodeBytecodeUsesAsNumber \| NodeBytecodeNeedsNegZero;
81345200 A	296	flags &= ~NodeBytecodeUsesAsOther;
93a37866 A	297
	298	node->child1()->mergeFlags(flags);
	299	node->child2()->mergeFlags(flags);
	300	break;
	301	}
	302
	303	case ArithDiv: {
81345200 A	304	flags \|= NodeBytecodeUsesAsNumber \| NodeBytecodeNeedsNegZero;
81345200 A	305	flags &= ~NodeBytecodeUsesAsOther;
93a37866 A	306
	307	node->child1()->mergeFlags(flags);
	308	node->child2()->mergeFlags(flags);
	309	break;
	310	}
	311
	312	case ArithMod: {
81345200 A	313	flags \|= NodeBytecodeUsesAsNumber \| NodeBytecodeNeedsNegZero;
81345200 A	314	flags &= ~NodeBytecodeUsesAsOther;
93a37866 A	315
	316	node->child1()->mergeFlags(flags);
	317	node->child2()->mergeFlags(flags);
	318	break;
	319	}
	320
	321	case GetByVal: {
81345200 A	322	node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
81345200 A	323	node->child2()->mergeFlags(NodeBytecodeUsesAsNumber \| NodeBytecodeUsesAsOther \| NodeBytecodeUsesAsInt \| NodeBytecodeUsesAsArrayIndex);
93a37866 A	324	break;
	325	}
	326
	327	case GetMyArgumentByValSafe: {
81345200	328	node->child1()->mergeFlags(NodeBytecodeUsesAsNumber \| NodeBytecodeUsesAsOther \| NodeBytecodeUsesAsInt \| NodeBytecodeUsesAsArrayIndex);
93a37866 A	329	break;
	330	}
	331
	332	case NewArrayWithSize: {
81345200 A	333	node->child1()->mergeFlags(NodeBytecodeUsesAsValue \| NodeBytecodeUsesAsInt \| NodeBytecodeUsesAsArrayIndex);
	334	break;
	335	}
	336
	337	case NewTypedArray: {
	338	// Negative zero is not observable. NaN versus undefined are only observable
	339	// in that you would get a different exception message. So, like, whatever: we
	340	// claim here that NaN v. undefined is observable.
	341	node->child1()->mergeFlags(NodeBytecodeUsesAsInt \| NodeBytecodeUsesAsNumber \| NodeBytecodeUsesAsOther \| NodeBytecodeUsesAsArrayIndex);
93a37866 A	342	break;
	343	}
	344
	345	case StringCharAt: {
81345200 A	346	node->child1()->mergeFlags(NodeBytecodeUsesAsValue);
81345200 A	347	node->child2()->mergeFlags(NodeBytecodeUsesAsValue \| NodeBytecodeUsesAsInt \| NodeBytecodeUsesAsArrayIndex);
93a37866 A	348	break;
	349	}
	350
	351	case ToString: {
81345200	352	node->child1()->mergeFlags(NodeBytecodeUsesAsNumber \| NodeBytecodeUsesAsOther);
93a37866 A	353	break;
	354	}
	355
	356	case ToPrimitive: {
	357	node->child1()->mergeFlags(flags);
	358	break;
	359	}
81345200 A	360
81345200 A	361	case PutByValDirect:
93a37866	362	case PutByVal: {
81345200 A	363	m_graph.varArgChild(node, 0)->mergeFlags(NodeBytecodeUsesAsValue);
	364	m_graph.varArgChild(node, 1)->mergeFlags(NodeBytecodeUsesAsNumber \| NodeBytecodeUsesAsOther \| NodeBytecodeUsesAsInt \| NodeBytecodeUsesAsArrayIndex);
	365	m_graph.varArgChild(node, 2)->mergeFlags(NodeBytecodeUsesAsValue);
	366	break;
	367	}
	368
	369	case Switch: {
	370	SwitchData* data = node->switchData();
	371	switch (data->kind) {
	372	case SwitchImm:
	373	// We don't need NodeBytecodeNeedsNegZero because if the cases are all integers
	374	// then -0 and 0 are treated the same. We don't need NodeBytecodeUsesAsOther
	375	// because if all of the cases are integers then NaN and undefined are
	376	// treated the same (i.e. they will take default).
	377	node->child1()->mergeFlags(NodeBytecodeUsesAsNumber \| NodeBytecodeUsesAsInt);
	378	break;
	379	case SwitchChar: {
	380	// We don't need NodeBytecodeNeedsNegZero because if the cases are all strings
	381	// then -0 and 0 are treated the same. We don't need NodeBytecodeUsesAsOther
	382	// because if all of the cases are single-character strings then NaN
	383	// and undefined are treated the same (i.e. they will take default).
	384	node->child1()->mergeFlags(NodeBytecodeUsesAsNumber);
	385	break;
	386	}
	387	case SwitchString:
	388	// We don't need NodeBytecodeNeedsNegZero because if the cases are all strings
	389	// then -0 and 0 are treated the same.
	390	node->child1()->mergeFlags(NodeBytecodeUsesAsNumber \| NodeBytecodeUsesAsOther);
	391	break;
	392	}
93a37866 A	393	break;
93a37866 A	394	}
81345200 A	395
	396	case Identity:
	397	// This would be trivial to handle but we just assert that we cannot see these yet.
	398	RELEASE_ASSERT_NOT_REACHED();
	399	break;
	400
	401	// Note: ArithSqrt, ArithSin, and ArithCos and other math intrinsics don't have special
	402	// rules in here because they are always followed by Phantoms to signify that if the
	403	// method call speculation fails, the bytecode may use the arguments in arbitrary ways.
	404	// This corresponds to that possibility of someone doing something like:
	405	// Math.sin = function(x) { doArbitraryThingsTo(x); }
93a37866 A	406
	407	default:
	408	mergeDefaultFlags(node);
	409	break;
	410	}
	411	}
	412
	413	bool m_allowNestedOverflowingAdditions;
81345200	414	bool m_changed;
93a37866 A	415	};
	416
	417	bool performBackwardsPropagation(Graph& graph)
	418	{
	419	SamplingRegion samplingRegion("DFG Backwards Propagation Phase");
	420	return runPhase<BackwardsPropagationPhase>(graph);
	421	}
	422
	423	} } // namespace JSC::DFG
	424
	425	#endif // ENABLE(DFG_JIT)
	426