Fix shadowed variable in faiss/impl/NNDescent.cpp

Summary:
Our upcoming compiler upgrade will require us not to have shadowed variables. Such variables have a _high_ bug rate and reduce readability, so we would like to avoid them even if the compiler was not forcing us to do so.

This codemod attempts to fix an instance of a shadowed variable. Please review with care: if it's failed the result will be a silent bug.

**What's a shadowed variable?**

Shadowed variables are variables in an inner scope with the same name as another variable in an outer scope. Having the same name for both variables might be semantically correct, but it can make the code confusing to read! It can also hide subtle bugs.

This diff fixes such an issue by renaming the variable.

 - If you approve of this diff, please use the "Accept & Ship" button :-)

Reviewed By: meyering

Differential Revision: D52582837

fbshipit-source-id: 275d20f940102030989f9bcfb4884891457b149c

faiss/impl/NNDescent.cpp

@@ -195,8 +195,9 @@ void NNDescent::update() {
         int l = 0;
 
         while ((l < maxl) && (c < S)) {
-            if (nn.pool[l].flag)
+            if (nn.pool[l].flag) {
                 ++c;
+            }
             ++l;
         }
         nn.M = l;
@@ -305,8 +306,9 @@ void NNDescent::generate_eval_set(
     for (int i = 0; i < c.size(); i++) {
         std::vector<Neighbor> tmp;
         for (int j = 0; j < N; j++) {
-            if (c[i] == j)
+            if (c[i] == j) {
                 continue; // skip itself
+            }
             float dist = qdis.symmetric_dis(c[i], j);
             tmp.push_back(Neighbor(j, dist, true));
         }
@@ -360,8 +362,9 @@ void NNDescent::init_graph(DistanceComputer& qdis) {
 
             for (int j = 0; j < S; j++) {
                 int id = tmp[j];
-                if (id == i)
+                if (id == i) {
                     continue;
+                }
                 float dist = qdis.symmetric_dis(i, id);
 
                 graph[i].pool.push_back(Neighbor(id, dist, true));
@@ -418,56 +421,59 @@ void NNDescent::search(
         float* dists,
         VisitedTable& vt) const {
     FAISS_THROW_IF_NOT_MSG(has_built, "The index is not build yet.");
-    int L = std::max(search_L, topk);
+    int L_2 = std::max(search_L, topk);
 
     // candidate pool, the K best items is the result.
-    std::vector<Neighbor> retset(L + 1);
+    std::vector<Neighbor> retset(L_2 + 1);
 
-    // Randomly choose L points to initialize the candidate pool
-    std::vector<int> init_ids(L);
+    // Randomly choose L_2 points to initialize the candidate pool
+    std::vector<int> init_ids(L_2);
     std::mt19937 rng(random_seed);
 
-    gen_random(rng, init_ids.data(), L, ntotal);
-    for (int i = 0; i < L; i++) {
+    gen_random(rng, init_ids.data(), L_2, ntotal);
+    for (int i = 0; i < L_2; i++) {
         int id = init_ids[i];
         float dist = qdis(id);
         retset[i] = Neighbor(id, dist, true);
     }
 
     // Maintain the candidate pool in ascending order
-    std::sort(retset.begin(), retset.begin() + L);
+    std::sort(retset.begin(), retset.begin() + L_2);
 
     int k = 0;
 
-    // Stop until the smallest position updated is >= L
-    while (k < L) {
-        int nk = L;
+    // Stop until the smallest position updated is >= L_2
+    while (k < L_2) {
+        int nk = L_2;
 
         if (retset[k].flag) {
             retset[k].flag = false;
             int n = retset[k].id;
 
             for (int m = 0; m < K; ++m) {
                 int id = final_graph[n * K + m];
-                if (vt.get(id))
+                if (vt.get(id)) {
                     continue;
+                }
 
                 vt.set(id);
                 float dist = qdis(id);
-                if (dist >= retset[L - 1].distance)
+                if (dist >= retset[L_2 - 1].distance) {
                     continue;
+                }
 
                 Neighbor nn(id, dist, true);
-                int r = insert_into_pool(retset.data(), L, nn);
+                int r = insert_into_pool(retset.data(), L_2, nn);
 
                 if (r < nk)
                     nk = r;
             }
         }
-        if (nk <= k)
+        if (nk <= k) {
             k = nk;
-        else
+        } else {
             ++k;
+        }
     }
     for (size_t i = 0; i < topk; i++) {
         indices[i] = retset[i].id;