[strong] Implement strong mode semantics for the count operation.

src/compiler/ast-graph-builder.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/ast-graph-builder.h"
 
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
 #include "src/compiler/js-type-feedback.h"
@@ skipping 2643 matching lines @@
           CreateVectorSlotPair(property->PropertyFeedbackSlot());
       old_value = BuildKeyedSuperLoad(receiver, home_object, key, pair);
       states.AddToNode(old_value, property->LoadId(),
                        OutputFrameStateCombine::Push());
       stack_depth = 3;
       break;
     }
   }
 
   // Convert old value into a number.
-  old_value = NewNode(javascript()->ToNumber(), old_value);
-  PrepareFrameState(old_value, expr->ToNumberId(),
-                    OutputFrameStateCombine::Push());
+  if (!is_strong(language_mode())) {
+    old_value = NewNode(javascript()->ToNumber(), old_value);
+    PrepareFrameState(old_value, expr->ToNumberId(),
+                      OutputFrameStateCombine::Push());
+  }
 
   // TODO(titzer): combine this framestate with the above?
   FrameStateBeforeAndAfter store_states(this, assign_type == KEYED_PROPERTY
                                                   ? expr->ToNumberId()
                                                   : BailoutId::None());
 
   // Save result for postfix expressions at correct stack depth.
   if (is_postfix) environment()->Poke(stack_depth, old_value);
 
   // Create node to perform +1/-1 operation.
   Node* value;
   {
     FrameStateBeforeAndAfter states(this, BailoutId::None());
     value =
         BuildBinaryOp(old_value, jsgraph()->OneConstant(), expr->binary_op());
-    // This should never deoptimize because we have converted to number
-    // before.
-    states.AddToNode(value, BailoutId::None(),
+    // This should never deoptimize outside strong mode because otherwise we
+    // have converted to number before.
+    states.AddToNode(value, is_strong(language_mode()) ? expr->ToNumberId()
+                                                       : BailoutId::None(),
                      OutputFrameStateCombine::Ignore());
   }
 
   // Store the value.
   VectorSlotPair feedback = CreateVectorSlotPair(expr->CountSlot());
   switch (assign_type) {
     case VARIABLE: {
       Variable* variable = expr->expression()->AsVariableProxy()->var();
       environment()->Push(value);
       BuildVariableAssignment(variable, value, expr->op(), feedback,
@@ skipping 1476 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8