Temporal dead zone behaviour for let bindings.

src/arm/full-codegen-arm.cc

Index: src/arm/full-codegen-arm.cc
diff --git a/src/arm/full-codegen-arm.cc b/src/arm/full-codegen-arm.cc
index 3116ca455bcd6b23646c98d2cd8a20da536bdb47..d5a1b5ffbd3758d1a87325b2daa153abc86a6757 100644
--- a/src/arm/full-codegen-arm.cc
+++ b/src/arm/full-codegen-arm.cc
@@ -700,12 +700,12 @@ void FullCodeGenerator::EmitDeclaration(Variable* variable,
     switch (slot->type()) {
       case Slot::PARAMETER:
       case Slot::LOCAL:
-        if (mode == Variable::CONST) {
-          __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-          __ str(ip, MemOperand(fp, SlotOffset(slot)));
-        } else if (function != NULL) {
+        if (function != NULL) {
           VisitForAccumulatorValue(function);
           __ str(result_register(), MemOperand(fp, SlotOffset(slot)));
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
+          __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
+          __ str(ip, MemOperand(fp, SlotOffset(slot)));
         }
         break;
 
@@ -724,20 +724,19 @@ void FullCodeGenerator::EmitDeclaration(Variable* variable,
           __ CompareRoot(r1, Heap::kCatchContextMapRootIndex);
           __ Check(ne, "Declaration in catch context.");
         }
-        if (mode == Variable::CONST) {
-          __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-          __ str(ip, ContextOperand(cp, slot->index()));
-          // No write barrier since the_hole_value is in old space.
-        } else if (function != NULL) {
+        if (function != NULL) {
           VisitForAccumulatorValue(function);
           __ str(result_register(), ContextOperand(cp, slot->index()));
           int offset = Context::SlotOffset(slot->index());
           // We know that we have written a function, which is not a smi.
           __ mov(r1, Operand(cp));
           __ RecordWrite(r1, Operand(offset), r2, result_register());
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
+          __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
+          __ str(ip, ContextOperand(cp, slot->index()));
+          // No write barrier since the_hole_value is in old space.
         }
         break;
-
       case Slot::LOOKUP: {
         __ mov(r2, Operand(variable->name()));
         // Declaration nodes are always introduced in one of two modes.
@@ -750,13 +749,13 @@ void FullCodeGenerator::EmitDeclaration(Variable* variable,
         // 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.
-        if (mode == Variable::CONST) {
-          __ LoadRoot(r0, Heap::kTheHoleValueRootIndex);
-          __ Push(cp, r2, r1, r0);
-        } else if (function != NULL) {
+        if (function != NULL) {
           __ Push(cp, r2, r1);
           // Push initial value for function declaration.
           VisitForStackValue(function);
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
+          __ LoadRoot(r0, Heap::kTheHoleValueRootIndex);
+          __ Push(cp, r2, r1, r0);
         } else {
           __ mov(r0, Operand(Smi::FromInt(0)));  // No initial value!
           __ Push(cp, r2, r1, r0);
@@ -1311,6 +1310,20 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
       __ cmp(r0, ip);
       __ LoadRoot(r0, Heap::kUndefinedValueRootIndex, eq);
       context()->Plug(r0);
+    } else if (var->mode() == Variable::LET) {
+      // Let bindings may be the hole value if they have not been initialized.
+      // Throw a type error in this case.
+      Label done;
+      MemOperand slot_operand = EmitSlotSearch(slot, r0);
+      __ ldr(r0, slot_operand);
+      __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
+      __ cmp(r0, ip);
+      __ b(ne, &done);
+      __ mov(r0, Operand(var->name()));
+      __ push(r0);
+      __ CallRuntime(Runtime::kThrowReferenceError, 1);
+      __ bind(&done);
+      context()->Plug(r0);
     } else {
       context()->Plug(slot);
     }
@@ -1891,6 +1904,59 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var,
     }
     __ bind(&skip);
 
+  } else if (var->mode() == Variable::LET && op != Token::INIT_LET) {
+    // Perform the assignment for non-const variables.  Const assignments
+    // are simply skipped.
+    Slot* slot = var->AsSlot();
+    switch (slot->type()) {
+      case Slot::PARAMETER:
+      case Slot::LOCAL: {
+        Label assign;
+        // Check for an initialized let binding.
+        __ ldr(r1, MemOperand(fp, SlotOffset(slot)));
+        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
+        __ cmp(r1, ip);
+        __ b(ne, &assign);
+        __ mov(r1, Operand(var->name()));
+        __ push(r1);
+        __ CallRuntime(Runtime::kThrowReferenceError, 1);
+        // Perform the assignment.
+        __ bind(&assign);
+        __ str(result_register(), MemOperand(fp, SlotOffset(slot)));
+        break;
+      }
+      case Slot::CONTEXT: {
+        // Let variables may be the hole value if they have not been
+        // initialized. Throw a type error in this case.
+        Label assign;
+        MemOperand target = EmitSlotSearch(slot, r1);
+        // Check for an initialized let binding.
+        __ ldr(r3, target);
+        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
+        __ cmp(r3, ip);
+        __ b(ne, &assign);
+        __ mov(r3, Operand(var->name()));
+        __ push(r3);
+        __ CallRuntime(Runtime::kThrowReferenceError, 1);
+        // Perform the assignment.
+        __ bind(&assign);
+        __ str(result_register(), target);
+        // RecordWrite may destroy all its register arguments.
+        __ mov(r3, result_register());
+        int offset = Context::SlotOffset(slot->index());
+        __ RecordWrite(r1, Operand(offset), r2, r3);
+        break;
+      }
+      case Slot::LOOKUP:
+        // Call the runtime for the assignment.
+        __ push(r0);  // Value.
+        __ mov(r1, Operand(slot->var()->name()));
+        __ mov(r0, Operand(Smi::FromInt(strict_mode_flag())));
+        __ Push(cp, r1, r0);  // Context, name, strict mode.
+        __ CallRuntime(Runtime::kStoreContextSlot, 4);
+        break;
+    }
+
   } else if (var->mode() != Variable::CONST) {
     // Perform the assignment for non-const variables.  Const assignments
     // are simply skipped.