Disable InferType if it was done and no changes after previous pass

This optimizatin allows to speedup PatternRewriter transformations by
reusing of preious type inferred expression instead of perform
InferType multiple times

Author: elvin-n

src/relay/ir/dataflow_matcher.cc

@@ -851,24 +851,32 @@ Expr PatternRewriter::Rewrite(const Array<DFPatternCallback>& callbacks, const E
   std::unordered_map<DFPatternCallback, bool, ObjectPtrHash, ObjectPtrEqual> done;
   do {
     last = post;
+    // We don't have to call InferType if previous pass has not modified anything
+    // We can just take previous typed state of the expression
+    bool types_invalidated = true;
     for (auto callback : callbacks) {
       if (!done[callback]) {
         auto before = post;
+        auto post_typed = post;
         callback_ = callback;
-        if (callback_->require_type) {
-          post = InferTypeWithModule(post, mod_);
+        if (callback_->require_type && types_invalidated) {
+          post_typed = InferTypeWithModule(post, mod_);
         }
         auto grouper = PatternGrouper();
-        groups_ = grouper.GroupMatches(callback_->pattern, post);
+        groups_ = grouper.GroupMatches(callback_->pattern, post_typed);
         gid_assignments_ = grouper.GetGIDAssignments();
         memo_.clear();
         VLOG(1) << "pre rewritten:" << std::endl << PrettyPrint(pre);
-        post = this->VisitExpr(post);
+        post = this->VisitExpr(post_typed);
         VLOG(1) << "post rewritten:" << std::endl << PrettyPrint(post);
         count++;
-        if (callback_->rewrite_once) {
-          bool current_equal = (*structural_equal)(before, post, false, true);
-          if (!current_equal) {
+        bool current_equal = (*structural_equal)(before, post, false, true);
+        if (callback_->require_type && current_equal) {
+          types_invalidated = false;
+          post = post_typed;
+        } else {
+          types_invalidated = true;
+          if (callback_->rewrite_once) {
             done[callback] = true;
           }
         }