Do not go to slow mode and back to fast in initializer blocks.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 954d043a9f532ef260064b349a4f56bd17e87b36..1949c316cb1d9de1dfedeff644ad81417106aa2b 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -2118,37 +2118,15 @@ void FullCodeGenerator::EmitNamedPropertyAssignment(Assignment* expr) {
   ASSERT(prop != NULL);
   ASSERT(prop->key()->AsLiteral() != NULL);
 
-  // If the assignment starts a block of assignments to the same object,
-  // change to slow case to avoid the quadratic behavior of repeatedly
-  // adding fast properties.
-  if (expr->starts_initialization_block()) {
-    __ push(result_register());
-    __ push(Operand(rsp, kPointerSize));  // Receiver is now under value.
-    __ CallRuntime(Runtime::kToSlowProperties, 1);
-    __ pop(result_register());
-  }
-
   // Record source code position before IC call.
   SetSourcePosition(expr->position());
   __ Move(rcx, prop->key()->AsLiteral()->handle());
-  if (expr->ends_initialization_block()) {
-    __ movq(rdx, Operand(rsp, 0));
-  } else {
-    __ pop(rdx);
-  }
+  __ pop(rdx);
   Handle<Code> ic = is_classic_mode()
       ? isolate()->builtins()->StoreIC_Initialize()
       : isolate()->builtins()->StoreIC_Initialize_Strict();
   CallIC(ic, RelocInfo::CODE_TARGET, expr->AssignmentFeedbackId());
 
-  // If the assignment ends an initialization block, revert to fast case.
-  if (expr->ends_initialization_block()) {
-    __ push(rax);  // Result of assignment, saved even if not needed.
-    __ push(Operand(rsp, kPointerSize));  // Receiver is under value.
-    __ CallRuntime(Runtime::kToFastProperties, 1);
-    __ pop(rax);
-    __ Drop(1);
-  }
   PrepareForBailoutForId(expr->AssignmentId(), TOS_REG);
   context()->Plug(rax);
 }
@@ -2157,23 +2135,8 @@ void FullCodeGenerator::EmitNamedPropertyAssignment(Assignment* expr) {
 void FullCodeGenerator::EmitKeyedPropertyAssignment(Assignment* expr) {
   // Assignment to a property, using a keyed store IC.
 
-  // If the assignment starts a block of assignments to the same object,
-  // change to slow case to avoid the quadratic behavior of repeatedly
-  // adding fast properties.
-  if (expr->starts_initialization_block()) {
-    __ push(result_register());
-    // Receiver is now under the key and value.
-    __ push(Operand(rsp, 2 * kPointerSize));
-    __ CallRuntime(Runtime::kToSlowProperties, 1);
-    __ pop(result_register());
-  }
-
   __ pop(rcx);
-  if (expr->ends_initialization_block()) {
-    __ movq(rdx, Operand(rsp, 0));  // Leave receiver on the stack for later.
-  } else {
-    __ pop(rdx);
-  }
+  __ pop(rdx);
   // Record source code position before IC call.
   SetSourcePosition(expr->position());
   Handle<Code> ic = is_classic_mode()
@@ -2181,15 +2144,6 @@ void FullCodeGenerator::EmitKeyedPropertyAssignment(Assignment* expr) {
       : isolate()->builtins()->KeyedStoreIC_Initialize_Strict();
   CallIC(ic, RelocInfo::CODE_TARGET, expr->AssignmentFeedbackId());
 
-  // If the assignment ends an initialization block, revert to fast case.
-  if (expr->ends_initialization_block()) {
-    __ pop(rdx);
-    __ push(rax);  // Result of assignment, saved even if not needed.
-    __ push(rdx);
-    __ CallRuntime(Runtime::kToFastProperties, 1);
-    __ pop(rax);
-  }
-
   PrepareForBailoutForId(expr->AssignmentId(), TOS_REG);
   context()->Plug(rax);
 }