harmony-scoping: make assignment to 'const' a late error.

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/machine-operator.h"
@@ skipping 2002 matching lines @@
     case Variable::PARAMETER:
     case Variable::LOCAL:
       // Local var, const, or let variable.
       if (mode == CONST_LEGACY && op == Token::INIT_CONST_LEGACY) {
         // Perform an initialization check for legacy const variables.
         Node* current = environment()->Lookup(variable);
         if (current->op() != the_hole->op()) {
           value = BuildHoleCheckSilent(current, value, current);
         }
       } else if (mode == CONST_LEGACY && op != Token::INIT_CONST_LEGACY) {
-        // Non-initializing assignments to legacy const is ignored.
+        // Non-initializing assignments to const is
+        // - exception in strict mode.
+        // - ignored in sloppy mode.
+        if (strict_mode() == STRICT) {
+          return BuildThrowConstAssignError(bailout_id);
+        }
         return value;
       } else if (mode == LET && op != Token::INIT_LET) {
         // Perform an initialization check for let declared variables.
         // Also note that the dynamic hole-check is only done to ensure that
         // this does not break in the presence of do-expressions within the
         // temporal dead zone of a let declared variable.
         Node* current = environment()->Lookup(variable);
         if (current->op() == the_hole->op()) {
           value = BuildThrowReferenceError(variable, bailout_id);
         } else if (value->opcode() == IrOpcode::kPhi) {
           value = BuildHoleCheckThrow(current, variable, value, bailout_id);
         }
       } else if (mode == CONST && op != Token::INIT_CONST) {

[rossberg, 2014/11/26 08:31:46]

Why not merge this case with the above?

[Dmitry Lomov (no reviews), 2014/11/26 08:52:32]

And extract the condition into IsNonInitializingAssignementToConst because it is
so unwieldy? Riiight.
There is way too much ado around a bunch of conditionals

[Dmitry Lomov (no reviews), 2014/11/26 10:30:56]

Actually, I realized that we also decided that non-initializing assignments to
(non-legacy) const should throw in all modes, so these cases are not unifiable.
Fixed here and in full codegen

-        // All assignments to const variables are early errors.
-        UNREACHABLE();
+        // Non-initializing assignments to const is
+        // - exception in strict mode.
+        // - ignored in sloppy mode.
+        if (strict_mode() == STRICT) {
+          return BuildThrowConstAssignError(bailout_id);
+        }
+        return value;
       }
       environment()->Bind(variable, value);
       return value;
     case Variable::CONTEXT: {
       // Context variable (potentially up the context chain).
       int depth = current_scope()->ContextChainLength(variable->scope());
       if (mode == CONST_LEGACY && op == Token::INIT_CONST_LEGACY) {
         // Perform an initialization check for legacy const variables.
         const Operator* op =
             javascript()->LoadContext(depth, variable->index(), false);
         Node* current = NewNode(op, current_context());
         value = BuildHoleCheckSilent(current, value, current);
       } else if (mode == CONST_LEGACY && op != Token::INIT_CONST_LEGACY) {
-        // Non-initializing assignments to legacy const is ignored.
+        // Non-initializing assignments to const is
+        // - exception in strict mode.
+        // - ignored in sloppy mode.
+        if (strict_mode() == STRICT) {
+          return BuildThrowConstAssignError(bailout_id);
+        }
         return value;
       } else if (mode == LET && op != Token::INIT_LET) {
         // Perform an initialization check for let declared variables.
         const Operator* op =
             javascript()->LoadContext(depth, variable->index(), false);
         Node* current = NewNode(op, current_context());
         value = BuildHoleCheckThrow(current, variable, value, bailout_id);
       } else if (mode == CONST && op != Token::INIT_CONST) {

[rossberg, 2014/11/26 08:31:46]

Same here.

-        // All assignments to const variables are early errors.
-        UNREACHABLE();
+        // Non-initializing assignments to const is
+        // - exception in strict mode.
+        // - ignored in sloppy mode.
+        if (strict_mode() == STRICT) {
+          return BuildThrowConstAssignError(bailout_id);
+        }
+        return value;
       }
       const Operator* op = javascript()->StoreContext(depth, variable->index());
       return NewNode(op, current_context(), value);
     }
     case Variable::LOOKUP: {
       // Dynamic lookup of context variable (anywhere in the chain).
       Node* name = jsgraph()->Constant(variable->name());
       Node* strict = jsgraph()->Constant(strict_mode());
       // TODO(mstarzinger): Use Runtime::kInitializeLegacyConstLookupSlot for
       // initializations of const declarations.
@@ skipping 73 matching lines @@
   // TODO(mstarzinger): Should be unified with the VisitThrow implementation.
   Node* variable_name = jsgraph()->Constant(variable->name());
   const Operator* op =
       javascript()->CallRuntime(Runtime::kThrowReferenceError, 1);
   Node* call = NewNode(op, variable_name);
   PrepareFrameState(call, bailout_id);
   return call;
 }
 
 
+Node* AstGraphBuilder::BuildThrowConstAssignError(BailoutId bailout_id) {
+  // TODO(mstarzinger): Should be unified with the VisitThrow implementation.
+  const Operator* op =
+      javascript()->CallRuntime(Runtime::kThrowConstAssignError, 0);
+  Node* call = NewNode(op);
+  PrepareFrameState(call, bailout_id);
+  return call;
+}
+
+
 Node* AstGraphBuilder::BuildBinaryOp(Node* left, Node* right, Token::Value op) {
   const Operator* js_op;
   switch (op) {
     case Token::BIT_OR:
       js_op = javascript()->BitwiseOr();
       break;
     case Token::BIT_AND:
       js_op = javascript()->BitwiseAnd();
       break;
     case Token::BIT_XOR:
@@ skipping 62 matching lines @@
 
 BitVector* AstGraphBuilder::GetVariablesAssignedInLoop(
     IterationStatement* stmt) {
   if (loop_assignment_analysis_ == NULL) return NULL;
   return loop_assignment_analysis_->GetVariablesAssignedInLoop(stmt);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8