[vm,aot] Improve performance of certain 'is' operations

runtime/vm/aot_optimizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/aot_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/branch_optimizer.h"
 #include "vm/cha.h"
 #include "vm/compiler.h"
@@ skipping 1336 matching lines @@
     if (cache != NULL &&
         cache->InstanceOfHasClassRange(type, &lower_limit, &upper_limit)) {
       // left.instanceof(type) =>
       //     _classRangeCheck(left.cid, lower_limit, upper_limit)
 
       LoadClassIdInstr* left_cid =
           new (Z) LoadClassIdInstr(new (Z) Value(left));
       InsertBefore(call, left_cid, NULL, FlowGraph::kValue);
       ConstantInstr* lower_cid =
           flow_graph()->GetConstant(Smi::Handle(Z, Smi::New(lower_limit)));
+
+      if (lower_limit == upper_limit) {

[Vyacheslav Egorov (Google), 2017/08/25 07:59:15]

Does it make sense to do a similar optimization for `as` Checks?

There is a code below that handles as checks.

Maybe we should unify handling of is and as more? It does not make sense that
they are so duplicated right now.

[alexmarkov, 2017/08/29 22:45:32]

I think you're right - 'as' and 'is' checks should be unified, preferably
lowered to the same kind of type test.

Without this unification, it doesn't look right to duplicate this optimization
for 'as' checks, because 'as' checks, unlike 'is' checks,  are implemented with
more heavyweight calls to helper functions and won't benefit much from this
particular optimization.

I'd like to consider unification of 'is' and 'as' type checks as a separate task
and approach it after implementing proper lowering pass.

Created issue: https://github.com/dart-lang/sdk/issues/30571.

+        StrictCompareInstr* check_cid = new (Z) StrictCompareInstr(
+            call->token_pos(), Token::kEQ_STRICT, new (Z) Value(left_cid),
+            new (Z) Value(lower_cid), /* number_check = */ false,
+            Thread::kNoDeoptId);
+        ReplaceCall(call, check_cid);
+        return;
+      }
+
       ConstantInstr* upper_cid =
           flow_graph()->GetConstant(Smi::Handle(Z, Smi::New(upper_limit)));
 
       ZoneGrowableArray<PushArgumentInstr*>* args =
           new (Z) ZoneGrowableArray<PushArgumentInstr*>(3);
       PushArgumentInstr* arg =
           new (Z) PushArgumentInstr(new (Z) Value(left_cid));
       InsertBefore(call, arg, NULL, FlowGraph::kEffect);
       args->Add(arg);
       arg = new (Z) PushArgumentInstr(new (Z) Value(lower_cid));
@@ skipping 721 matching lines @@
                                   FlowGraph::kEffect);
         current_iterator()->RemoveCurrentFromGraph();
       }
     }
   }
 }
 
 #endif  // DART_PRECOMPILER
 
 }  // namespace dart