Fix shadowed variable in faiss/IndexPQ.cpp (facebookresearch#3959)

Summary:
Pull Request resolved: facebookresearch#3959

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: D64398686

fbshipit-source-id: 44c60ea6e99d9542acf5af15adba6cdccda95577

faiss/IndexPQ.cpp

@@ -159,16 +159,16 @@ void IndexPQ::search(
     FAISS_THROW_IF_NOT(is_trained);
 
     const SearchParametersPQ* params = nullptr;
-    Search_type_t search_type = this->search_type;
+    Search_type_t search_type_2 = this->search_type;
 
     if (iparams) {
         params = dynamic_cast<const SearchParametersPQ*>(iparams);
         FAISS_THROW_IF_NOT_MSG(params, "invalid search params");
         FAISS_THROW_IF_NOT_MSG(!params->sel, "selector not supported");
-        search_type = params->search_type;
+        search_type_2 = params->search_type;
     }
 
-    if (search_type == ST_PQ) { // Simple PQ search
+    if (search_type_2 == ST_PQ) { // Simple PQ search
 
         if (metric_type == METRIC_L2) {
             float_maxheap_array_t res = {
@@ -183,19 +183,19 @@ void IndexPQ::search(
         indexPQ_stats.ncode += n * ntotal;
 
     } else if (
-            search_type == ST_polysemous ||
-            search_type == ST_polysemous_generalize) {
+            search_type_2 == ST_polysemous ||
+            search_type_2 == ST_polysemous_generalize) {
         FAISS_THROW_IF_NOT(metric_type == METRIC_L2);
-        int polysemous_ht =
+        int polysemous_ht_2 =
                 params ? params->polysemous_ht : this->polysemous_ht;
         search_core_polysemous(
                 n,
                 x,
                 k,
                 distances,
                 labels,
-                polysemous_ht,
-                search_type == ST_polysemous_generalize);
+                polysemous_ht_2,
+                search_type_2 == ST_polysemous_generalize);
 
     } else { // code-to-code distances
 
@@ -215,7 +215,7 @@ void IndexPQ::search(
             }
         }
 
-        if (search_type == ST_SDC) {
+        if (search_type_2 == ST_SDC) {
             float_maxheap_array_t res = {
                     size_t(n), size_t(k), labels, distances};
 
@@ -227,7 +227,7 @@ void IndexPQ::search(
             int_maxheap_array_t res = {
                     size_t(n), size_t(k), labels, idistances.get()};
 
-            if (search_type == ST_HE) {
+            if (search_type_2 == ST_HE) {
                 hammings_knn_hc(
                         &res,
                         q_codes.get(),
@@ -236,7 +236,7 @@ void IndexPQ::search(
                         pq.code_size,
                         true);
 
-            } else if (search_type == ST_generalized_HE) {
+            } else if (search_type_2 == ST_generalized_HE) {
                 generalized_hammings_knn_hc(
                         &res,
                         q_codes.get(),
@@ -322,13 +322,13 @@ void IndexPQ::search_core_polysemous(
         idx_t k,
         float* distances,
         idx_t* labels,
-        int polysemous_ht,
+        int polysemous_ht_2,
         bool generalized_hamming) const {
     FAISS_THROW_IF_NOT(k > 0);
     FAISS_THROW_IF_NOT(pq.nbits == 8);
 
-    if (polysemous_ht == 0) {
-        polysemous_ht = pq.nbits * pq.M + 1;
+    if (polysemous_ht_2 == 0) {
+        polysemous_ht_2 = pq.nbits * pq.M + 1;
     }
 
     // PQ distance tables
@@ -374,7 +374,7 @@ void IndexPQ::search_core_polysemous(
                     k,
                     heap_dis,
                     heap_ids,
-                    polysemous_ht);
+                    polysemous_ht_2);
 
         } else { // generalized hamming
             switch (pq.code_size) {
@@ -387,7 +387,7 @@ void IndexPQ::search_core_polysemous(
                 k,                                               \
                 heap_dis,                                        \
                 heap_ids,                                        \
-                polysemous_ht);                                  \
+                polysemous_ht_2);                                \
         break;
                 DISPATCH(8)
                 DISPATCH(16)
@@ -401,7 +401,7 @@ void IndexPQ::search_core_polysemous(
                                 k,
                                 heap_dis,
                                 heap_ids,
-                                polysemous_ht);
+                                polysemous_ht_2);
                     } else {
                         bad_code_size++;
                     }
@@ -516,8 +516,8 @@ struct PreSortedArray {
     int N;
 
     explicit PreSortedArray(int N) : N(N) {}
-    void init(const T* x) {
-        this->x = x;
+    void init(const T* x_2) {
+        this->x = x_2;
     }
     // get smallest value
     T get_0() {
@@ -557,11 +557,11 @@ struct SortedArray {
         perm.resize(N);
     }
 
-    void init(const T* x) {
-        this->x = x;
+    void init(const T* x_2) {
+        this->x = x_2;
         for (int n = 0; n < N; n++)
             perm[n] = n;
-        ArgSort<T> cmp = {x};
+        ArgSort<T> cmp = {x_2};
         std::sort(perm.begin(), perm.end(), cmp);
     }
 
@@ -639,8 +639,8 @@ struct SemiSortedArray {
         k_factor = 4;
     }
 
-    void init(const T* x) {
-        this->x = x;
+    void init(const T* x_2) {
+        this->x = x_2;
         for (int n = 0; n < N; n++)
             perm[n] = n;
         k = 0;