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

package unit;

import java.util.*;

/**
 * Unit test for llvm-0004: DomConditionCache::registerBranch O(B^2) defect.
 *
 * Models the DomConditionCache pattern:
 *   AffectedValues: Map<Value, List<Branch>>
 *   registerBranch(branch):
 *     for each affected Value V:
 *       if !AV[V].contains(branch):   // O(|AV[V]|) — the defect
 *         AV[V].add(branch)
 *
 * Slow path: is_contained() = List.contains() — O(B) per branch per value
 * Fast path: pre-built HashSet — O(1) per branch per value
 */
public class LlvmDomConditionCacheTest {

    // ---- slow path: mirrors the defective LLVM code ----

    static long slowRegisterBranches(int numBranches, int numValuesPerBranch) {
        // AffectedValues: for each Value index, a list of branch indices
        List<List<Integer>> affectedValues = new ArrayList<>();
        for (int v = 0; v < numValuesPerBranch; v++)
            affectedValues.add(new ArrayList<>());

        long ops = 0;
        for (int b = 0; b < numBranches; b++) {
            // Each branch affects numValuesPerBranch shared values
            for (int v = 0; v < numValuesPerBranch; v++) {
                List<Integer> av = affectedValues.get(v);
                // O(|av|) scan — the defect
                ops++;
                boolean found = false;
                for (int existing : av) {   // linear scan
                    ops++;
                    if (existing == b) { found = true; break; }
                }
                if (!found) av.add(b);
            }
        }
        return ops;
    }

    // ---- fast path: pre-built set for O(1) membership ----

    static long fastRegisterBranches(int numBranches, int numValuesPerBranch) {
        List<Set<Integer>> affectedSets = new ArrayList<>();
        for (int v = 0; v < numValuesPerBranch; v++)
            affectedSets.add(new HashSet<>());

        long ops = 0;
        for (int b = 0; b < numBranches; b++) {
            for (int v = 0; v < numValuesPerBranch; v++) {
                Set<Integer> av = affectedSets.get(v);
                ops++;  // O(1) hash lookup
                av.add(b);
            }
        }
        return ops;
    }

    // ---- correctness: both paths produce same AV lists ----

    static boolean correctnessCheck(int branches, int valuesPerBranch) {
        List<List<Integer>> slowAV = new ArrayList<>();
        for (int v = 0; v < valuesPerBranch; v++)
            slowAV.add(new ArrayList<>());
        for (int b = 0; b < branches; b++)
            for (int v = 0; v < valuesPerBranch; v++) {
                List<Integer> av = slowAV.get(v);
                if (!av.contains(b)) av.add(b);
            }

        List<Set<Integer>> fastAV = new ArrayList<>();
        for (int v = 0; v < valuesPerBranch; v++)
            fastAV.add(new HashSet<>());
        for (int b = 0; b < branches; b++)
            for (int v = 0; v < valuesPerBranch; v++)
                fastAV.get(v).add(b);

        for (int v = 0; v < valuesPerBranch; v++) {
            Set<Integer> slowSet = new HashSet<>(slowAV.get(v));
            if (!slowSet.equals(fastAV.get(v))) return false;
        }
        return true;
    }

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

        // Test 1: correctness small
        total++;
        if (correctnessCheck(10, 3)) { pass++; System.out.println("PASS test1: correctness (10 branches, 3 values)"); }
        else System.out.println("FAIL test1: correctness");

        // Test 2: correctness larger
        total++;
        if (correctnessCheck(50, 5)) { pass++; System.out.println("PASS test2: correctness (50 branches, 5 values)"); }
        else System.out.println("FAIL test2: correctness");

        // Test 3: slow path op count is O(B^2) for shared single value
        // B branches, 1 shared value: slow ops = B + B*(B-1)/2 (triangular)
        total++;
        int B = 100;
        long slowOps = slowRegisterBranches(B, 1);
        long fastOps = fastRegisterBranches(B, 1);
        // slow should be >> fast; slow is roughly B*(B+1)/2
        boolean slowIsQuadratic = slowOps > (long) B * B / 3;
        boolean fastIsLinear = fastOps <= B + 5;
        if (slowIsQuadratic && fastIsLinear) {
            pass++;
            System.out.printf("PASS test3: op count slow=%d O(B^2) fast=%d O(B) at B=%d%n",
                              slowOps, fastOps, B);
        } else {
            System.out.printf("FAIL test3: slow=%d fast=%d B=%d (expected slow>>fast)%n",
                              slowOps, fastOps, B);
        }

        // Test 4: speedup ratio >= 10x at B=200
        total++;
        B = 200;
        slowOps = slowRegisterBranches(B, 1);
        fastOps = fastRegisterBranches(B, 1);
        long ratio = slowOps / Math.max(fastOps, 1);
        if (ratio >= 10) {
            pass++;
            System.out.printf("PASS test4: speedup %dx at B=%d (slow=%d fast=%d)%n",
                              ratio, B, slowOps, fastOps);
        } else {
            System.out.printf("FAIL test4: speedup only %dx at B=%d%n", ratio, B);
        }

        // Test 5: zero branches edge case
        total++;
        if (slowRegisterBranches(0, 5) == 0 && fastRegisterBranches(0, 5) == 0) {
            pass++;
            System.out.println("PASS test5: empty input");
        } else {
            System.out.println("FAIL test5: empty input");
        }

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