Source/WTF/wtf/GraphOrdering.h

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#pragma once

#include <algorithm>
#include <array>
#include <wtf/BitVector.h>
#include <wtf/Vector.h>

namespace WTF {

enum class GraphOrder : uint8_t {
    PreOrder,
    PostOrder,
};

// Most general form: for every node reachable from `roots`, appends projection(index) into
// `output` in the requested order. `visited` must be sized to graph.numNodes(); it is set for
// every node this call appends (callers may reuse it afterwards). `roots` is any iterable of
// graph nodes; falsy roots (e.g. null Node) are skipped.
template<typename Graph, typename Roots, typename Container, typename Projection>
void appendNodeOrderFromRoots(Graph& graph, const Roots& roots, GraphOrder order, BitVector& visited, Container& output, NOESCAPE const Projection& projection)
{
    constexpr unsigned revisitFlag = 1u << 31;
    ASSERT(static_cast<unsigned>(graph.numNodes()) < revisitFlag);

    Vector<unsigned, 32> stack;
    for (auto root : roots) {
        if (root)
            stack.append(graph.index(root));
    }

    while (!stack.isEmpty()) {
        unsigned entry = stack.takeLast();

        if (entry & revisitFlag) {
            // Post-visit: all successors have been emitted.
            output.append(projection(entry & ~revisitFlag));
            continue;
        }

        if (visited.quickGet(entry))
            continue;
        visited.quickSet(entry);

        if (order == GraphOrder::PreOrder)
            output.append(projection(entry));
        else
            stack.append(entry | revisitFlag);

        for (auto successor : graph.successors(graph.node(entry))) {
            unsigned successorIndex = graph.index(successor);
            if (!visited.quickGet(successorIndex))
                stack.append(successorIndex);
        }
    }
}

template<typename Graph, typename Container, typename Projection>
void appendNodeOrder(Graph& graph, GraphOrder order, BitVector& visited, Container& output, NOESCAPE const Projection& projection)
{
    std::array<typename Graph::Node, 1> roots { graph.root() };
    appendNodeOrderFromRoots(graph, roots, order, visited, output, projection);
}

// Appends node indices (as held by the graph) into `output`. Used by index-based dataflow such as
// WTF::Liveness and WTF::Dominators. `visited` is caller-owned.
template<typename Graph, typename Container>
void appendNodeIndicesInOrder(Graph& graph, GraphOrder order, BitVector& visited, Container& output)
{
    appendNodeOrder(graph, order, visited, output, [](unsigned index) { return index; });
}

template<typename Graph, typename Roots, typename Container>
void appendNodeIndicesInOrder(Graph& graph, const Roots& roots, GraphOrder order, BitVector& visited, Container& output)
{
    appendNodeOrderFromRoots(graph, roots, order, visited, output, [](unsigned index) { return index; });
}

// Appends graph nodes into `output`. Used by B3/Air/DFG which produce block lists. The visited set
// is allocated internally.
template<typename Graph, typename Container>
void appendNodesInOrder(Graph& graph, GraphOrder order, Container& output)
{
    BitVector visited(graph.numNodes());
    appendNodeOrder(graph, order, visited, output, [&](unsigned index) { return graph.node(index); });
}

template<typename Graph, typename Roots, typename Container>
void appendNodesInOrder(Graph& graph, const Roots& roots, GraphOrder order, Container& output)
{
    BitVector visited(graph.numNodes());
    appendNodeOrderFromRoots(graph, roots, order, visited, output, [&](unsigned index) { return graph.node(index); });
}

} // namespace WTF

using WTF::GraphOrder;
using WTF::appendNodeOrder;
using WTF::appendNodeOrderFromRoots;
using WTF::appendNodeIndicesInOrder;
using WTF::appendNodesInOrder;