DFGCFAPhase.cpp   [plain text]

/*
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#include "config.h"
#include "DFGCFAPhase.h"

#if ENABLE(DFG_JIT)

#include "DFGAbstractInterpreterInlines.h"
#include "DFGGraph.h"
#include "DFGInPlaceAbstractState.h"
#include "DFGPhase.h"
#include "DFGSafeToExecute.h"
#include "OperandsInlines.h"
#include "JSCInlines.h"

namespace JSC { namespace DFG {

class CFAPhase : public Phase {
public:
    CFAPhase(Graph& graph)
        : Phase(graph, "control flow analysis")
        , m_state(graph)
        , m_interpreter(graph, m_state)
        , m_verbose(Options::verboseCFA())
    {
    }
    
    bool run()
    {
        ASSERT(m_graph.m_form == ThreadedCPS || m_graph.m_form == SSA);
        ASSERT(m_graph.m_unificationState == GloballyUnified);
        ASSERT(m_graph.m_refCountState == EverythingIsLive);
        
        m_count = 0;
        
        if (m_verbose && !shouldDumpGraphAtEachPhase()) {
            dataLog("Graph before CFA:\n");
            m_graph.dump();
        }
        
        // This implements a pseudo-worklist-based forward CFA, except that the visit order
        // of blocks is the bytecode program order (which is nearly topological), and
        // instead of a worklist we just walk all basic blocks checking if cfaShouldRevisit
        // is set to true. This is likely to balance the efficiency properties of both
        // worklist-based and forward fixpoint-based approaches. Like a worklist-based
        // approach, it won't visit code if it's meaningless to do so (nothing changed at
        // the head of the block or the predecessors have not been visited). Like a forward
        // fixpoint-based approach, it has a high probability of only visiting a block
        // after all predecessors have been visited. Only loops will cause this analysis to
        // revisit blocks, and the amount of revisiting is proportional to loop depth.
        
        m_state.initialize();
        
        do {
            m_changed = false;
            performForwardCFA();
        } while (m_changed);
        
        if (m_graph.m_form != SSA) {
            ASSERT(!m_changed);
            
            // Widen the abstract values at the block that serves as the must-handle OSR entry.
            for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
                BasicBlock* block = m_graph.block(blockIndex);
                if (!block)
                    continue;
                
                if (!block->isOSRTarget)
                    continue;
                if (block->bytecodeBegin != m_graph.m_plan.osrEntryBytecodeIndex)
                    continue;
                
                bool changed = false;
                for (size_t i = m_graph.m_plan.mustHandleValues.size(); i--;) {
                    int operand = m_graph.m_plan.mustHandleValues.operandForIndex(i);
                    JSValue value = m_graph.m_plan.mustHandleValues[i];
                    Node* node = block->variablesAtHead.operand(operand);
                    if (!node)
                        continue;
                    
                    AbstractValue& target = block->valuesAtHead.operand(operand);
                    changed |= target.mergeOSREntryValue(m_graph, value);
                    target.fixTypeForRepresentation(
                        m_graph, resultFor(node->variableAccessData()->flushFormat()));
                }
                
                if (changed || !block->cfaHasVisited) {
                    m_changed = true;
                    block->cfaShouldRevisit = true;
                }
            }

            // Propagate any of the changes we just introduced.
            while (m_changed) {
                m_changed = false;
                performForwardCFA();
            }
            
            // Make sure we record the intersection of all proofs that we ever allowed the
            // compiler to rely upon.
            for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
                BasicBlock* block = m_graph.block(blockIndex);
                if (!block)
                    continue;
                
                block->intersectionOfCFAHasVisited &= block->cfaHasVisited;
                for (unsigned i = block->intersectionOfPastValuesAtHead.size(); i--;)
                    block->intersectionOfPastValuesAtHead[i].filter(block->valuesAtHead[i]);
            }
        }
        
        return true;
    }
    
private:
    void performBlockCFA(BasicBlock* block)
    {
        if (!block)
            return;
        if (!block->cfaShouldRevisit)
            return;
        if (m_verbose)
            dataLog("   Block ", *block, ":\n");
        m_state.beginBasicBlock(block);
        if (m_verbose) {
            dataLog("      head vars: ", block->valuesAtHead, "\n");
            if (m_graph.m_form == SSA)
                dataLog("      head regs: ", mapDump(block->ssa->valuesAtHead), "\n");
        }
        for (unsigned i = 0; i < block->size(); ++i) {
            if (m_verbose) {
                Node* node = block->at(i);
                dataLogF("      %s @%u: ", Graph::opName(node->op()), node->index());
                
                if (!safeToExecute(m_state, m_graph, node))
                    dataLog("(UNSAFE) ");
                
                dataLog(m_state.variables(), " ", m_interpreter);
                
                dataLogF("\n");
            }
            if (!m_interpreter.execute(i)) {
                if (m_verbose)
                    dataLogF("         Expect OSR exit.\n");
                break;
            }
        }
        if (m_verbose) {
            dataLogF("      tail regs: ");
            m_interpreter.dump(WTF::dataFile());
            dataLogF("\n");
        }
        m_changed |= m_state.endBasicBlock(MergeToSuccessors);
        
        if (m_verbose) {
            dataLog("      tail vars: ", block->valuesAtTail, "\n");
            if (m_graph.m_form == SSA)
                dataLog("      head regs: ", mapDump(block->ssa->valuesAtTail), "\n");
        }
    }
    
    void performForwardCFA()
    {
        ++m_count;
        if (m_verbose)
            dataLogF("CFA [%u]\n", ++m_count);
        
        for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex)
            performBlockCFA(m_graph.block(blockIndex));
    }

private:
    InPlaceAbstractState m_state;
    AbstractInterpreter<InPlaceAbstractState> m_interpreter;
    
    bool m_verbose;
    
    bool m_changed;
    unsigned m_count;
};

bool performCFA(Graph& graph)
{
    SamplingRegion samplingRegion("DFG CFA Phase");
    return runPhase<CFAPhase>(graph);
}

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)