java-topology/defects/spidermonkey/unit/SpiderMonkeyRemapperTest.java

package unit;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * SM-0002: MDefinitionRemapper::lookup() O(N) linear scan inside loop-unroll cloning.
 *
 * Models:
 *   - SlowRemapper  — Vector<Pair> linear lookup, O(V) per lookup  → O(V²) per body clone
 *   - FastRemapper  — HashMap<K,V> lookup, O(1) per lookup          → O(V)  per body clone
 *
 * Compile: javac -d . *.java   (from defects/spidermonkey/unit/)
 * Run:     java -ea unit.SpiderMonkeyRemapperTest
 */
public class SpiderMonkeyRemapperTest {

    // ---- slow path: Vector<Pair> linear scan --------------------------------

    static class SlowRemapper {
        static long opCount;

        static class Pair {
            final int original;
            int replacement;
            Pair(int o) { original = o; replacement = o; }
        }

        private final List<Pair> pairs = new ArrayList<>();

        void enregister(int original) {
            pairs.add(new Pair(original));
        }

        int lookup(int original) {
            for (Pair p : pairs) {
                opCount++;
                if (p.original == original)
                    return p.replacement;
            }
            return -1; // not found
        }

        void update(int original, int replacement) {
            for (Pair p : pairs) {
                if (p.original == original) {
                    p.replacement = replacement;
                    return;
                }
            }
        }
    }

    // ---- fast path: HashMap O(1) lookup -------------------------------------

    static class FastRemapper {
        static long opCount;
        private final HashMap<Integer, Integer> map = new HashMap<>();

        void enregister(int original) {
            map.put(original, original);
        }

        int lookup(int original) {
            opCount++;  // one hash lookup
            Integer v = map.get(original);
            return v == null ? -1 : v;
        }

        void update(int original, int replacement) {
            map.put(original, replacement);
        }
    }

    // ---- simulate loop body clone -------------------------------------------
    // For each of V values in the mapper, clone K operands that each call lookup().
    // Operands reference value (V-1) — the last registered — to hit worst-case
    // scan length for SlowRemapper (must scan entire list every time).

    static long simulateClone(boolean fast, int V, int K) {
        int worstCaseKey = V - 1; // last in the vector → full scan each time
        if (fast) {
            FastRemapper.opCount = 0;
            FastRemapper mapper = new FastRemapper();
            for (int i = 0; i < V; i++) mapper.enregister(i);
            // clone V instructions, each with K operands
            for (int insn = 0; insn < V; insn++) {
                for (int op = 0; op < K; op++) {
                    mapper.lookup(worstCaseKey);
                }
            }
            return FastRemapper.opCount;
        } else {
            SlowRemapper.opCount = 0;
            SlowRemapper mapper = new SlowRemapper();
            for (int i = 0; i < V; i++) mapper.enregister(i);
            for (int insn = 0; insn < V; insn++) {
                for (int op = 0; op < K; op++) {
                    mapper.lookup(worstCaseKey);
                }
            }
            return SlowRemapper.opCount;
        }
    }

    // ---- tests --------------------------------------------------------------

    static int passed = 0;
    static int total  = 0;

    static void check(String name, boolean cond) {
        total++;
        if (cond) {
            passed++;
        } else {
            System.out.println("FAIL: " + name);
        }
    }

    public static void main(String[] args) {
        // correctness: both return same result
        {
            SlowRemapper slow = new SlowRemapper();
            FastRemapper fast = new FastRemapper();
            int[] vals = {10, 20, 30, 40, 50};
            for (int v : vals) { slow.enregister(v); fast.enregister(v); }
            slow.update(20, 99); fast.update(20, 99);
            check("slow lookup 10", slow.lookup(10) == 10);
            check("fast lookup 10", fast.lookup(10) == 10);
            check("slow lookup 20 updated", slow.lookup(20) == 99);
            check("fast lookup 20 updated", fast.lookup(20) == 99);
            check("slow lookup 50", slow.lookup(50) == 50);
            check("fast lookup 50", fast.lookup(50) == 50);
            check("slow lookup miss", slow.lookup(99) == -1);
            check("fast lookup miss", fast.lookup(99) == -1);
        }

        // op-count scaling: V values, K=3 operands each
        int[] sizes = {10, 30, 60, 100, 150};
        int K = 3;

        System.out.println();
        System.out.printf("%-8s %12s %12s %8s%n", "V", "slow_ops", "fast_ops", "ratio");
        for (int V : sizes) {
            long slowOps = simulateClone(false, V, K);
            long fastOps = simulateClone(true,  V, K);
            double ratio = (double) slowOps / fastOps;
            System.out.printf("%-8d %12d %12d %8.1f%n", V, slowOps, fastOps, ratio);

            // slow ops should be O(V²): roughly V * K * V/2 on average
            // fast ops should be O(V):  exactly V * K
            long expectedFast = (long) V * K;
            // slow worst-case: each lookup scans all V entries (key is last)
            long expectedSlow = (long) V * K * V;
            check("fast ops == V*K for V=" + V, fastOps == expectedFast);
            check("slow ops == V*K*V for V=" + V, slowOps == expectedSlow);
            // ratio should be exactly V (slow scans V items per lookup)
            check("slow/fast ratio == V for V=" + V, Math.abs(ratio - V) < 0.01);
        }

        System.out.println();
        System.out.printf("%d/%d PASS%n", passed, total);
        if (passed != total) System.exit(1);
    }
}