java-topology/defects/jsc/unit/JSCBytecodeBasicBlockTest.java

package unit;

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

/**
 * JSC-0001: BytecodeBasicBlock::computeImpl() O(B²×T) edge linking.
 *
 * Models the inner loop in BytecodeBasicBlock.cpp lines 181-193:
 *   - SlowLinker: for each branch block, scan all B blocks and call
 *                 Vector::contains(jumpTargets) for each — O(B × T) per branch
 *   - FastLinker: load jump targets into HashSet first — O(B + T) per branch
 *
 * Compile: javac -d . *.java   (from defects/jsc/unit/)
 * Run:     java -ea unit.JSCBytecodeBasicBlockTest
 */
public class JSCBytecodeBasicBlockTest {

    // ---- slow path: Vector<Offset> linear contains --------------------------

    static class SlowLinker {
        static long opCount;

        /**
         * @param blockCount   total basic blocks (B)
         * @param jumpTargets  list of target offsets (size T)
         * @return             number of (block, target) linkage operations found
         */
        static int link(int blockCount, List<Integer> jumpTargets) {
            int linked = 0;
            // Simulate: for (auto& otherBlock : basicBlocks)
            for (int blockId = 0; blockId < blockCount; blockId++) {
                // Simulate: bytecodeOffsetsJumpedTo.contains(otherBlock.leaderOffset())
                for (Integer target : jumpTargets) {
                    opCount++;
                    if (target == blockId) {
                        linked++;
                        break;
                    }
                }
            }
            return linked;
        }
    }

    // ---- fast path: HashSet<Offset> O(1) lookup -----------------------------

    static class FastLinker {
        static long opCount;

        static int link(int blockCount, List<Integer> jumpTargets) {
            // Build HashSet once: O(T)
            HashSet<Integer> targetSet = new HashSet<>(jumpTargets);
            opCount += jumpTargets.size(); // insertions

            int linked = 0;
            // Simulate: for (auto& otherBlock : basicBlocks)
            for (int blockId = 0; blockId < blockCount; blockId++) {
                opCount++; // one hash lookup
                if (targetSet.contains(blockId)) {
                    linked++;
                }
            }
            return linked;
        }
    }

    // ---- helpers ------------------------------------------------------------

    static List<Integer> makeTargets(int blockCount, int T) {
        // T evenly-spaced target block offsets
        List<Integer> targets = new ArrayList<>(T);
        int step = Math.max(1, blockCount / T);
        for (int i = 0; i < T && i * step < blockCount; i++)
            targets.add(i * step);
        return targets;
    }

    // ---- 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 find same number of links
        {
            int B = 20, T = 4;
            List<Integer> targets = makeTargets(B, T);
            SlowLinker.opCount = 0;
            FastLinker.opCount = 0;
            int slowLinks = SlowLinker.link(B, targets);
            int fastLinks = FastLinker.link(B, targets);
            check("slow and fast agree on link count", slowLinks == fastLinks);
            check("linked count == T", slowLinks == T);
        }

        // op-count scaling
        int[] blockCounts = {50, 100, 200, 500};
        int[] switchSizes = {10, 50, 200, 500};

        System.out.println();
        System.out.printf("%-8s %-8s %14s %14s %10s%n",
            "B", "T", "slow_ops", "fast_ops", "ratio");

        for (int B : blockCounts) {
            for (int T : switchSizes) {
                if (T > B) continue;
                List<Integer> targets = makeTargets(B, T);
                SlowLinker.opCount = 0;
                FastLinker.opCount = 0;
                int slowLinks = SlowLinker.link(B, targets);
                int fastLinks = FastLinker.link(B, targets);
                check("results agree B=" + B + " T=" + T, slowLinks == fastLinks);

                long slow = SlowLinker.opCount;
                long fast = FastLinker.opCount;
                double ratio = (double) slow / fast;
                System.out.printf("%-8d %-8d %14d %14d %10.1f%n",
                    B, T, slow, fast, ratio);

                // slow ops ~ O(B × T), fast ops ~ O(B + T)
                // ratio should grow with min(B,T)
                int minBT = Math.min(B, T);
                check("slow > fast for B=" + B + " T=" + T, slow > fast);
                // for large T, ratio should be at least T/4
                if (T >= 50) {
                    check("ratio >= T/4 for T=" + T, ratio >= (double) T / 4);
                }
            }
        }

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