Block scoped const variables.

src/ia32/full-codegen-ia32.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 693 matching lines @@
 
 
 void FullCodeGenerator::EmitDeclaration(VariableProxy* proxy,
                                         VariableMode mode,
                                         FunctionLiteral* function,
                                         int* global_count) {
   // If it was not possible to allocate the variable at compile time, we
   // need to "declare" it at runtime to make sure it actually exists in the
   // local context.
   Variable* variable = proxy->var();
+  bool binding_needs_init =

[fschneider, 2011/10/24 12:58:13]

EmitDeclaration is used in two places. Is it possible to use
variable->binding_needs_init() instead here?

[Steven, 2011/10/24 14:05:18]

Unfortunately for DYNAMIC_GLOBAL variables we can only get the mode used in the
declaration from the declaration object and not from the variable itself. It
does for example occur with eval('var foo;') in global scope. We can't pass the
declaration because it is also used for the function variable of a named
function expression, which doesn't have a declaration object. I will leave
cleaning this up for another hypothetical CL.
On 2011/10/24 12:58:13, fschneider wrote:

[fschneider, 2011/10/24 15:33:44]

Yes, passing a declaration object would be the right way, but it's fine to leave
it as is for this change.

On 2011/10/24 14:05:18, Steven wrote:

+      mode == CONST || mode == CONST_HARMONY || mode == LET;
   switch (variable->location()) {
     case Variable::UNALLOCATED:
       ++(*global_count);
       break;
 
     case Variable::PARAMETER:
     case Variable::LOCAL:
       if (function != NULL) {
         Comment cmnt(masm_, "[ Declaration");
         VisitForAccumulatorValue(function);
         __ mov(StackOperand(variable), result_register());
-      } else if (mode == CONST || mode == LET) {
+      } else if (binding_needs_init) {
         Comment cmnt(masm_, "[ Declaration");
         __ mov(StackOperand(variable),
                Immediate(isolate()->factory()->the_hole_value()));
       }
       break;
 
     case Variable::CONTEXT:
       // The variable in the decl always resides in the current function
       // context.
       ASSERT_EQ(0, scope()->ContextChainLength(variable->scope()));
@@ skipping 11 matching lines @@
         __ mov(ContextOperand(esi, variable->index()), result_register());
         // We know that we have written a function, which is not a smi.
         __ RecordWriteContextSlot(esi,
                                   Context::SlotOffset(variable->index()),
                                   result_register(),
                                   ecx,
                                   kDontSaveFPRegs,
                                   EMIT_REMEMBERED_SET,
                                   OMIT_SMI_CHECK);
         PrepareForBailoutForId(proxy->id(), NO_REGISTERS);
-      } else if (mode == CONST || mode == LET) {
+      } else if (binding_needs_init) {
         Comment cmnt(masm_, "[ Declaration");
         __ mov(ContextOperand(esi, variable->index()),
                Immediate(isolate()->factory()->the_hole_value()));
         // No write barrier since the hole value is in old space.
         PrepareForBailoutForId(proxy->id(), NO_REGISTERS);
       }
       break;
 
     case Variable::LOOKUP: {
       Comment cmnt(masm_, "[ Declaration");
       __ push(esi);
       __ push(Immediate(variable->name()));
-      // Declaration nodes are always introduced in one of three modes.
-      ASSERT(mode == VAR || mode == CONST || mode == LET);
-      PropertyAttributes attr = (mode == CONST) ? READ_ONLY : NONE;
+      // Declaration nodes are always introduced in one of four modes.
+      ASSERT(mode == VAR ||
+             mode == CONST ||
+             mode == CONST_HARMONY ||
+             mode == LET);
+      PropertyAttributes attr = (mode == CONST || mode == CONST_HARMONY)
+          ? READ_ONLY : NONE;
       __ push(Immediate(Smi::FromInt(attr)));
       // Push initial value, if any.
       // Note: For variables we must not push an initial value (such as
       // 'undefined') because we may have a (legal) redeclaration and we
       // must not destroy the current value.
       increment_stack_height(3);
       if (function != NULL) {
         VisitForStackValue(function);
-      } else if (mode == CONST || mode == LET) {
+      } else if (binding_needs_init) {
         __ push(Immediate(isolate()->factory()->the_hole_value()));
         increment_stack_height();
       } else {
         __ push(Immediate(Smi::FromInt(0)));  // Indicates no initial value.
         increment_stack_height();
       }
       __ CallRuntime(Runtime::kDeclareContextSlot, 4);
       decrement_stack_height(4);
       break;
     }
@@ skipping 407 matching lines @@
   // introducing variables.  In those cases, we do not want to
   // perform a runtime call for all variables in the scope
   // containing the eval.
   if (var->mode() == DYNAMIC_GLOBAL) {
     EmitLoadGlobalCheckExtensions(var, typeof_state, slow);
     __ jmp(done);
   } else if (var->mode() == DYNAMIC_LOCAL) {
     Variable* local = var->local_if_not_shadowed();
     __ mov(eax, ContextSlotOperandCheckExtensions(local, slow));
     if (local->mode() == CONST ||
+        local->mode() == CONST_HARMONY ||
         local->mode() == LET) {
       __ cmp(eax, isolate()->factory()->the_hole_value());
       __ j(not_equal, done);
       if (local->mode() == CONST) {
         __ mov(eax, isolate()->factory()->undefined_value());
-      } else {  // LET
+      } else {  // LET || CONST_HARMONY
         __ push(Immediate(var->name()));
         __ CallRuntime(Runtime::kThrowReferenceError, 1);
       }
     }
     __ jmp(done);
   }
 }
 
 
 void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
@@ skipping 15 matching lines @@
       context()->Plug(eax);
       break;
     }
 
     case Variable::PARAMETER:
     case Variable::LOCAL:
     case Variable::CONTEXT: {
       Comment cmnt(masm_, var->IsContextSlot()
                               ? "Context variable"
                               : "Stack variable");
-      if (var->mode() != LET && var->mode() != CONST) {
+      if (!var->binding_needs_init()) {
         context()->Plug(var);
       } else {
         // Let and const need a read barrier.
         Label done;
         GetVar(eax, var);
         __ cmp(eax, isolate()->factory()->the_hole_value());
         __ j(not_equal, &done, Label::kNear);
-        if (var->mode() == LET) {
+        if (var->mode() == LET || var->mode() == CONST_HARMONY) {
+          // Throw a reference error when using an uninitialized let/const
+          // binding in harmony mode.
           __ push(Immediate(var->name()));
           __ CallRuntime(Runtime::kThrowReferenceError, 1);
-        } else {  // CONST
+        } else {
+          // Uninitalized const bindings outside of harmony mode are unholed.
+          ASSERT(var->mode() == CONST);
           __ mov(eax, isolate()->factory()->undefined_value());
         }
         __ bind(&done);
         context()->Plug(eax);
       }
       break;
     }
 
     case Variable::LOOKUP: {
       Label done, slow;
@@ skipping 662 matching lines @@
       __ CallRuntime(Runtime::kThrowReferenceError, 1);
       __ bind(&assign);
       __ mov(location, eax);
       if (var->IsContextSlot()) {
         __ mov(edx, eax);
         int offset = Context::SlotOffset(var->index());
         __ RecordWriteContextSlot(ecx, offset, edx, ebx, kDontSaveFPRegs);
       }
     }
 
-  } else if (var->mode() != CONST) {
-    // Assignment to var or initializing assignment to let.
+  } else if (!var->is_const_mode() || op == Token::INIT_CONST_HARMONY) {
+    // Assignment to var or initializing assignment to let/const
+    // in harmony mode.
     if (var->IsStackAllocated() || var->IsContextSlot()) {
       MemOperand location = VarOperand(var, ecx);
       if (FLAG_debug_code && op == Token::INIT_LET) {
         // Check for an uninitialized let binding.
         __ mov(edx, location);
         __ cmp(edx, isolate()->factory()->the_hole_value());
         __ Check(equal, "Let binding re-initialization.");
       }
       // Perform the assignment.
       __ mov(location, eax);
@@ skipping 2430 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32