Fix unique_index method on assoc arrays with values differing from the keys (#7616)

Signed-off-by: Pawel Klopotek <pklopotek@internships.antmicro.com>

docs/CONTRIBUTORS

@@ -218,6 +218,7 @@ Paul Bowen-Huggett
 Paul Swirhun
 Paul Wright
 Pawel Jewstafjew
+Pawel Klopotek
 Pawel Kojma
 Pawel Sagan
 Pengcheng Xu

include/verilated_types.h

@@ -1090,7 +1090,7 @@ public:
     }
     VlQueue<T_Key> unique_index() const {
         VlQueue<T_Key> out;
-        std::set<T_Key> saw;
+        std::set<T_Value> saw;
         for (const auto& i : m_map) {
             auto it = saw.find(i.second);
             if (it == saw.end()) {

test_regress/t/t_assoc_method.v

@@ -23,6 +23,7 @@ module t;
     int qv[$];  // Value returns
     int qi[$];  // Index returns
     point points_q[int];
+    point points_qe[int]; // Empty points
     point points_qv[$];
     int i;
     bit b;
@@ -58,6 +59,12 @@ module t;
     qi.sort;
     `checkp(qi, "'{'h0, 'h1, 'h5}");
 
+    qi = points_qe.unique_index();
+    `checkp(qi, "'{}");
+
+    qi = points_q.unique_index();
+    `checkh(qi.size, 3);
+
     qi = points_q.find_first_index with (item.x == 1);
     `checkp(qi, "'{'h0}");
     qi = points_q.find_first_index with (item.x == 10);