java-topology/defects/llvm/unit/LlvmAssumptionCacheTransferTest.java

package unit;

import java.util.*;

/**
 * Unit test for llvm-0005: AssumptionCache::transferAffectedValuesInCache O(N*M) defect.
 *
 * Models the pattern:
 *   for (auto &A : src_list)         // O(N) iterations
 *     if (!is_contained(dst_list, A)) // O(M) linear scan — the defect
 *       dst_list.push_back(A);
 *
 * Slow path: List.contains() — O(N*M) total
 * Fast path: pre-built HashSet from dst — O(N+M) total
 */
public class LlvmAssumptionCacheTransferTest {

    // Simulate a ResultElem: just an integer assume-id
    // is_contained checks by value equality

    static long slowTransfer(List<Integer> dst, List<Integer> src) {
        long ops = 0;
        for (int a : src) {                 // O(N)
            ops++;
            boolean found = false;
            for (int d : dst) {             // O(M) linear scan
                ops++;
                if (d == a) { found = true; break; }
            }
            if (!found) dst.add(a);
        }
        return ops;
    }

    static long fastTransfer(List<Integer> dst, List<Integer> src) {
        long ops = 0;
        // Build set from dst once: O(M)
        Set<Integer> dstSet = new HashSet<>(dst);
        ops += dst.size();  // building the set

        for (int a : src) {                 // O(N)
            ops++;
            if (dstSet.add(a)) {            // O(1)
                dst.add(a);
            }
        }
        return ops;
    }

    static boolean correctnessCheck(List<Integer> dstInit, List<Integer> src) {
        // slow
        List<Integer> slowDst = new ArrayList<>(dstInit);
        slowTransfer(slowDst, src);

        // fast
        List<Integer> fastDst = new ArrayList<>(dstInit);
        fastTransfer(fastDst, src);

        return new HashSet<>(slowDst).equals(new HashSet<>(fastDst));
    }

    static List<Integer> makeList(int from, int to) {
        List<Integer> l = new ArrayList<>();
        for (int i = from; i < to; i++) l.add(i);
        return l;
    }

    public static void main(String[] args) {
        int pass = 0, total = 0;

        // Test 1: no overlap
        total++;
        if (correctnessCheck(makeList(0, 5), makeList(5, 10))) {
            pass++; System.out.println("PASS test1: no overlap");
        } else System.out.println("FAIL test1: no overlap");

        // Test 2: full overlap (src already in dst — nothing added)
        total++;
        if (correctnessCheck(makeList(0, 10), makeList(0, 10))) {
            pass++; System.out.println("PASS test2: full overlap");
        } else System.out.println("FAIL test2: full overlap");

        // Test 3: partial overlap
        total++;
        if (correctnessCheck(makeList(0, 5), makeList(3, 8))) {
            pass++; System.out.println("PASS test3: partial overlap");
        } else System.out.println("FAIL test3: partial overlap");

        // Test 4: op count shows O(N*M) vs O(N+M)
        total++;
        int N = 200, M = 200;
        List<Integer> dst = makeList(0, M);
        List<Integer> src = makeList(M / 2, M / 2 + N);  // half overlap
        List<Integer> dstForSlow = new ArrayList<>(dst);
        List<Integer> dstForFast = new ArrayList<>(dst);
        long slowOps = slowTransfer(dstForSlow, src);
        long fastOps = fastTransfer(dstForFast, src);
        // slow should be roughly N*M/2 (each src item scans half of dst on average)
        boolean slowIsQuadratic = slowOps > (long) N * M / 4;
        boolean fastIsLinear = fastOps <= N + M + 10;
        if (slowIsQuadratic && fastIsLinear) {
            pass++;
            System.out.printf("PASS test4: op count slow=%d O(N*M) fast=%d O(N+M) N=%d M=%d%n",
                              slowOps, fastOps, N, M);
        } else {
            System.out.printf("FAIL test4: slow=%d fast=%d (expected slow>>fast)%n", slowOps, fastOps);
        }

        // Test 5: speedup >= 10x
        total++;
        long ratio = slowOps / Math.max(fastOps, 1);
        if (ratio >= 10) {
            pass++;
            System.out.printf("PASS test5: speedup %dx (slow=%d fast=%d)%n",
                              ratio, slowOps, fastOps);
        } else {
            System.out.printf("FAIL test5: speedup only %dx%n", ratio);
        }

        // Test 6: empty dst
        total++;
        if (correctnessCheck(new ArrayList<>(), makeList(0, 5))) {
            pass++; System.out.println("PASS test6: empty dst");
        } else System.out.println("FAIL test6: empty dst");

        // Test 7: empty src
        total++;
        if (correctnessCheck(makeList(0, 5), new ArrayList<>())) {
            pass++; System.out.println("PASS test7: empty src");
        } else System.out.println("FAIL test7: empty src");

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