Merge #10534: Clarify prevector::erase and avoid swap-to-clear

e241a63 Clarify prevector::erase and avoid swap-to-clear (Pieter Wuille)

Tree-SHA512: fa7602038feb4417158df13ee7c0351673acf38f8a824e75889710344c46a9b8d5f6059faeb521f73e48b7ad3e1a238a9e433e4b44f7c3b9085ff08ef65271fa

src/prevector.h

@@ -387,6 +387,12 @@ public:
     }
 
     iterator erase(iterator first, iterator last) {
+        // Erase is not allowed to the change the object's capacity. That means
+        // that when starting with an indirectly allocated prevector with
+        // size and capacity > N, the result may be a still indirectly allocated
+        // prevector with size <= N and capacity > N. A shrink_to_fit() call is
+        // necessary to switch to the (more efficient) directly allocated
+        // representation (with capacity N and size <= N).
         iterator p = first;
         char* endp = (char*)&(*end());
         if (!std::is_trivially_destructible<T>::value) {

src/script/script.h

@@ -645,8 +645,9 @@ public:
 
     void clear()
     {
-        // The default std::vector::clear() does not release memory.
-        CScriptBase().swap(*this);
+        // The default prevector::clear() does not release memory
+        CScriptBase::clear();
+        shrink_to_fit();
     }
 
     template<typename Stream>