VM: Improve single-target polymorphic calls.

runtime/vm/jit_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/jit_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/branch_optimizer.h"
 #include "vm/cha.h"
 #include "vm/compiler.h"
@@ skipping 2650 matching lines @@
       new(Z) AssertAssignableInstr(call->token_pos(),
                                    new(Z) Value(left),
                                    new(Z) Value(type_args),
                                    type,
                                    Symbols::InTypeCast(),
                                    call->deopt_id());
   ReplaceCall(call, assert_as);
 }
 
 
+static bool IsDenseCidRange(const ICData& unary_checks) {

[Vyacheslav Egorov (Google), 2016/04/01 10:53:59]

I am a bit concerned that we have two functions that do the same (they are even
called slightly differently): see CheckClassInstr::IsDenseSwitch.

[Florian Schneider, 2016/04/01 15:58:43]

Changed to use a single function CheckClassInstr::IsDenseCidRange.

+  if (unary_checks.GetReceiverClassIdAt(0) == kSmiCid) return false;
+  intptr_t max = 0;
+  intptr_t min = kIntptrMax;
+  for (intptr_t i = 0; i < unary_checks.NumberOfChecks(); ++i) {
+    intptr_t cid = unary_checks.GetCidAt(i);
+    if (cid < min) min = cid;
+    if (cid > max) max = cid;
+  }
+  return (max - min) < kBitsPerWord;
+}
+
+
 // Tries to optimize instance call by replacing it with a faster instruction
 // (e.g, binary op, field load, ..).
 void JitOptimizer::VisitInstanceCall(InstanceCallInstr* instr) {
   if (!instr->HasICData() || (instr->ic_data()->NumberOfUsedChecks() == 0)) {
     return;
   }
   const Token::Kind op_kind = instr->token_kind();
 
   // Type test is special as it always gets converted into inlined code.
   if (Token::IsTypeTestOperator(op_kind)) {
     ReplaceWithInstanceOf(instr);
     return;
   }
 
   if (Token::IsTypeCastOperator(op_kind)) {
     ReplaceWithTypeCast(instr);
     return;
   }
 
   const ICData& unary_checks =
       ICData::ZoneHandle(Z, instr->ic_data()->AsUnaryClassChecks());
 
+  const bool is_dense = IsDenseCidRange(unary_checks);
   const intptr_t max_checks = (op_kind == Token::kEQ)
       ? FLAG_max_equality_polymorphic_checks
       : FLAG_max_polymorphic_checks;
   if ((unary_checks.NumberOfChecks() > max_checks) &&
+      !is_dense &&
       flow_graph()->InstanceCallNeedsClassCheck(
           instr, RawFunction::kRegularFunction)) {
     // Too many checks, it will be megamorphic which needs unary checks.
     instr->set_ic_data(&unary_checks);
     return;
   }
 
   if ((op_kind == Token::kASSIGN_INDEX) && TryReplaceWithIndexedOp(instr)) {
     return;
   }
@@ skipping 45 matching lines @@
         Function::Handle(Z, unary_checks.GetTargetAt(0)).kind();
     if (!flow_graph()->InstanceCallNeedsClassCheck(instr, function_kind)) {
       PolymorphicInstanceCallInstr* call =
           new(Z) PolymorphicInstanceCallInstr(instr, unary_checks,
                                               /* call_with_checks = */ false);
       instr->ReplaceWith(call, current_iterator());
       return;
     }
   }
 
-  if (unary_checks.NumberOfChecks() <= FLAG_max_polymorphic_checks) {
+  if ((unary_checks.NumberOfChecks() <= FLAG_max_polymorphic_checks) ||
+      (has_one_target && is_dense)) {
     bool call_with_checks;
     if (has_one_target && FLAG_polymorphic_with_deopt) {
       // Type propagation has not run yet, we cannot eliminate the check.
       AddReceiverCheck(instr);
       // Call can still deoptimize, do not detach environment from instr.
       call_with_checks = false;
     } else {
       call_with_checks = true;
     }
     PolymorphicInstanceCallInstr* call =
@@ skipping 349 matching lines @@
 
   // Discard the environment from the original instruction because the store
   // can't deoptimize.
   instr->RemoveEnvironment();
   ReplaceCall(instr, store);
   return true;
 }
 
 
 }  // namespace dart