Remove CONST_LEGACY VariableMode

src/crankshaft/hydrogen.cc

Index: src/crankshaft/hydrogen.cc
diff --git a/src/crankshaft/hydrogen.cc b/src/crankshaft/hydrogen.cc
index 7f2ce828e572b956c60bed2c54a78bcfb9ac8a9d..d284c03aa93bb989cc9fef53de210236cd4c7ec5 100644
--- a/src/crankshaft/hydrogen.cc
+++ b/src/crankshaft/hydrogen.cc
@@ -6956,9 +6956,6 @@ void HOptimizedGraphBuilder::HandleCompoundAssignment(Assignment* expr) {
 
       case VariableLocation::PARAMETER:
       case VariableLocation::LOCAL:
-        if (var->mode() == CONST_LEGACY)  {
-          return Bailout(kUnsupportedConstCompoundAssignment);
-        }
         if (var->mode() == CONST) {
           return Bailout(kNonInitializerAssignmentToConst);
         }
@@ -6988,9 +6985,7 @@ void HOptimizedGraphBuilder::HandleCompoundAssignment(Assignment* expr) {
             mode = HStoreContextSlot::kCheckDeoptimize;
             break;
           case CONST:
-            return Bailout(kNonInitializerAssignmentToConst);
-          case CONST_LEGACY:
-            if (is_strict(function_language_mode())) {
+            if (var->throw_on_const_assignment(function_language_mode())) {

[adamk, 2016/08/11 01:02:39]

For Crankshaft, I suspect we could safely drop this branch and always bail out
if const assignment ever happens. But I'm not sure what caused the handling to
get added in the first place...

               return Bailout(kNonInitializerAssignmentToConst);
             } else {
               return ast_context()->ReturnValue(Pop());
@@ -7062,26 +7057,13 @@ void HOptimizedGraphBuilder::VisitAssignment(Assignment* expr) {
 
     if (var->mode() == CONST) {
       if (expr->op() != Token::INIT) {
-        return Bailout(kNonInitializerAssignmentToConst);
-      }
-    } else if (var->mode() == CONST_LEGACY) {
-      if (expr->op() != Token::INIT) {
-        if (is_strict(function_language_mode())) {
+        if (var->throw_on_const_assignment(function_language_mode())) {
           return Bailout(kNonInitializerAssignmentToConst);
         } else {
           CHECK_ALIVE(VisitForValue(expr->value()));
           return ast_context()->ReturnValue(Pop());
         }
       }
-
-      // TODO(adamk): Is this required? Legacy const variables are always
-      // initialized before use.
-      if (var->IsStackAllocated()) {
-        // We insert a use of the old value to detect unsupported uses of const
-        // variables (e.g. initialization inside a loop).
-        HValue* old_value = environment()->Lookup(var);
-        Add<HUseConst>(old_value);
-      }
     }
 
     if (proxy->IsArguments()) return Bailout(kAssignmentToArguments);
@@ -7137,10 +7119,10 @@ void HOptimizedGraphBuilder::VisitAssignment(Assignment* expr) {
               mode = HStoreContextSlot::kCheckDeoptimize;
               break;
             case CONST:
-              // This case is checked statically so no need to
-              // perform checks here
-              UNREACHABLE();
-            case CONST_LEGACY:
+              // If we reached this point, the only possibility
+              // is a sloppy assignment to a function name.
+              DCHECK(function_language_mode() == SLOPPY &&
+                     !var->throw_on_const_assignment(SLOPPY));
               return ast_context()->ReturnValue(Pop());
             default:
               mode = HStoreContextSlot::kNoCheck;
@@ -10755,9 +10737,6 @@ void HOptimizedGraphBuilder::VisitCountOperation(CountOperation* expr) {
 
   if (proxy != NULL) {
     Variable* var = proxy->var();
-    if (var->mode() == CONST_LEGACY)  {
-      return Bailout(kUnsupportedCountOperationWithConst);
-    }
     if (var->mode() == CONST) {
       return Bailout(kNonInitializerAssignmentToConst);
     }