Improve code for !identical(a, b):

runtime/vm/intermediate_language.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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 1225 matching lines @@
     instantiator_type_arguments()->BindTo(null_constant);
   }
   return this;
 }
 
 
 Instruction* BranchInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   // Only handle strict-compares.
   if (comparison()->IsStrictCompare()) {
     Definition* replacement = comparison()->Canonicalize(optimizer);
-    if (replacement == comparison() || replacement == NULL) return this;
+    if ((replacement == comparison()) || (replacement == NULL)) {
+      return this;
+    }
     ComparisonInstr* comp = replacement->AsComparison();
-    if ((comp == NULL) || comp->CanDeoptimize()) return this;
+    if ((comp == NULL) || comp->CanDeoptimize()) {
+      return this;
+    }
 
     // Check that comparison is not serving as a pending deoptimization target
     // for conversions.
     for (intptr_t i = 0; i < comp->InputCount(); i++) {
       if (comp->RequiredInputRepresentation(i) !=
           comp->InputAt(i)->definition()->representation()) {
         return this;
       }
     }
 
@@ skipping 12 matching lines @@
       ASSERT(comp->input_use_list() == NULL);
       comp->ClearSSATempIndex();
       comp->ClearTempIndex();
     }
   }
   return this;
 }
 
 
 Definition* StrictCompareInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
-  if (!right()->BindsToConstant()) return this;
+  if (!right()->BindsToConstant()) {
+    return this;
+  }
   const Object& right_constant = right()->BoundConstant();
   Definition* left_defn = left()->definition();
   // TODO(fschneider): Handle other cases: e === false and e !== true/false.
   // Handles e === true.
   if ((kind() == Token::kEQ_STRICT) &&
       (right_constant.raw() == Bool::True().raw()) &&
       (left()->Type()->ToCid() == kBoolCid)) {
     // Return left subexpression as the replacement for this instruction.
     return left_defn;
   }
+  // x = (a === b);  y = x !== true; -> y = a !== b.
+  // In order to merge two strict comares, 'left_strict' must have only one use.
+  // Do not check left's cid as it is required to be a strict compare.
+  StrictCompareInstr* left_strict = left_defn->AsStrictCompare();
+  if ((kind() == Token::kNE_STRICT) &&
+      (right_constant.raw() == Bool::True().raw()) &&
+      (left_strict != NULL) &&
+      (left_strict->HasOnlyUse(left()))) {
+    left_strict->set_kind(Token::NegateComparison(left_strict->kind()));
+    return left_strict;
+  }
+
   return this;
 }
 
 
 Instruction* CheckClassInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   // TODO(vegorov): Replace class checks with null checks when ToNullableCid
   // matches.
 
   const intptr_t value_cid = value()->Type()->ToCid();
   if (value_cid == kDynamicCid) {
@@ skipping 1040 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart