opt4: simplify_minof (#223)

libursa/QueryOptimizer.cpp

@@ -2,6 +2,13 @@
 
 #include <vector>
 
+// Returns a query that represents every element in the dataset.
+// There's no magic here, AND() just behaves like this.
+Query q_everything() {
+    std::vector<Query> queries;
+    return std::move(q_and(std::move(queries)));
+}
+
 // Run the optimization pases on subqueries.
 // After this step, every subquery should be maximally optimized,
 // So I believe there's no need to run this in a loop.
@@ -76,6 +83,27 @@ Query deduplicate_primitives(Query &&q, bool *changed) {
     return std::move(Query(q.get_type(), std::move(newqueries)));
 }
 
+// Minof is the slowest operation, so replace it by others if possible.
+// This may also enable other optimizations to take place.
+// MIN 5 OF (a, b, c, d, e) --> AND(a, b, c, d, e)
+// MIN 1 OF (a, b, c, d, e) --> OR(a, b, c, d, e)
+// MIN 0 OF (a, b, c, d, e) --> everything()
+Query simplify_minof(Query &&q, bool *changed) {
+    if (q.get_type() == QueryType::MIN_OF) {
+        if (q.as_count() == q.as_queries().size()) {
+            *changed = true;
+            return std::move(q_and(std::move(q.as_queries())));
+        } else if (q.as_count() == 1) {
+            *changed = true;
+            return std::move(q_or(std::move(q.as_queries())));
+        } else if (q.as_count() == 0) {
+            *changed = true;
+            return std::move(q_everything());
+        }
+    }
+    return std::move(q);
+}
+
 Query q_optimize(Query &&q) {
     if (q.get_type() == QueryType::PRIMITIVE) {
         // Nothing to improve here.
@@ -89,6 +117,7 @@ Query q_optimize(Query &&q) {
         q = flatten_trivial_operations(std::move(q), &changed);
         q = inline_suboperations(std::move(q), &changed);
         q = deduplicate_primitives(std::move(q), &changed);
+        q = simplify_minof(std::move(q), &changed);
     }
 
     return std::move(q);

libursa/Version.h.in

@@ -9,5 +9,5 @@ constexpr std::string_view ursadb_format_version = "1.5.0";
 // Project version.
 // Consider updating the version tag when doing PRs.
 // clang-format off
-constexpr std::string_view ursadb_version_string = "@PROJECT_VERSION@+opt3";
+constexpr std::string_view ursadb_version_string = "@PROJECT_VERSION@+opt4";
 // clang-format on