[hydrogen] don't bailout assignments to consts

src/hydrogen.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 3267 matching lines @@
       if (value == graph()->GetConstantHole()) {
         ASSERT(variable->mode() == CONST ||
                variable->mode() == CONST_HARMONY ||
                variable->mode() == LET);
         return Bailout("reference to uninitialized variable");
       }
       return ast_context()->ReturnValue(value);
     }
 
     case Variable::CONTEXT: {
-      if (variable->mode() == CONST) {
-        return Bailout("reference to const context slot");
-      }
       HValue* context = BuildContextChainWalk(variable);
       HLoadContextSlot* instr = new(zone()) HLoadContextSlot(context, variable);
       return ast_context()->ReturnInstruction(instr, expr->id());
     }
 
     case Variable::LOOKUP:
       return Bailout("reference to a variable which requires dynamic lookup");
   }
 }
 
@@ skipping 497 matching lines @@
   VariableProxy* proxy = target->AsVariableProxy();
   Property* prop = target->AsProperty();
   ASSERT(proxy == NULL || prop == NULL);
 
   // We have a second position recorded in the FullCodeGenerator to have
   // type feedback for the binary operation.
   BinaryOperation* operation = expr->binary_operation();
 
   if (proxy != NULL) {
     Variable* var = proxy->var();
-    if (var->mode() == CONST || var->mode() == LET)  {
-      return Bailout("unsupported let or const compound assignment");
+    if (var->mode() == LET)  {
+      return Bailout("unsupported let compound assignment");
     }
 
     CHECK_ALIVE(VisitForValue(operation));
 
     switch (var->location()) {
       case Variable::UNALLOCATED:
         HandleGlobalVariableAssignment(var,
                                        Top(),
                                        expr->position(),
                                        expr->AssignmentId());
         break;
 
       case Variable::PARAMETER:
       case Variable::LOCAL:
+        if (var->mode() == CONST)  {
+          return Bailout("unsupported const compound assignment");
+        }
         Bind(var, Top());
         break;
 
       case Variable::CONTEXT: {
         // Bail out if we try to mutate a parameter value in a function
         // using the arguments object.  We do not (yet) correctly handle the
         // arguments property of the function.
         if (info()->scope()->arguments() != NULL) {
           // Parameters will be allocated to context slots.  We have no
           // direct way to detect that the variable is a parameter so we do
           // a linear search of the parameter variables.
           int count = info()->scope()->num_parameters();
           for (int i = 0; i < count; ++i) {
             if (var == info()->scope()->parameter(i)) {
               Bailout(
                   "assignment to parameter, function uses arguments object");
             }
           }
         }
 
+        HStoreContextSlot::Mode mode;
+
+        switch (var->mode()) {
+          case LET:
+            mode = HStoreContextSlot::kCheckDeoptimize;
+            break;
+          case CONST:
+            return ast_context()->ReturnValue(Pop());
+          case CONST_HARMONY:
+            UNREACHABLE();

[fschneider, 2011/12/13 16:15:00]

Maybe a short comment that this is checked statically and can't occur therefore.

+          default:
+            mode = HStoreContextSlot::kNoCheck;
+        }
+
         HValue* context = BuildContextChainWalk(var);
-        HStoreContextSlot::Mode mode =
-            (var->mode() == LET || var->mode() == CONST_HARMONY)
-            ? HStoreContextSlot::kAssignCheck : HStoreContextSlot::kAssign;
         HStoreContextSlot* instr =
             new(zone()) HStoreContextSlot(context, var->index(), mode, Top());
         AddInstruction(instr);
         if (instr->HasObservableSideEffects()) {
           AddSimulate(expr->AssignmentId());
         }
         break;
       }
 
       case Variable::LOOKUP:
@@ skipping 90 matching lines @@
 
   if (expr->is_compound()) {
     HandleCompoundAssignment(expr);
     return;
   }
 
   if (prop != NULL) {
     HandlePropertyAssignment(expr);
   } else if (proxy != NULL) {
     Variable* var = proxy->var();
+
     if (var->mode() == CONST) {
       if (expr->op() != Token::INIT_CONST) {
-        return Bailout("non-initializer assignment to const");
+        CHECK_ALIVE(VisitForValue(expr->value()));
+        return ast_context()->ReturnValue(Pop());
       }
-      if (!var->IsStackAllocated()) {
-        return Bailout("assignment to const context slot");
+
+      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);
+        AddInstruction(new HUseConst(old_value));
       }
-      // 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);
-      AddInstruction(new HUseConst(old_value));
     } else if (var->mode() == CONST_HARMONY) {
       if (expr->op() != Token::INIT_CONST_HARMONY) {
         return Bailout("non-initializer assignment to const");
       }
     }
 
     if (proxy->IsArguments()) return Bailout("assignment to arguments");
 
     // Handle the assignment.
     switch (var->location()) {
@@ skipping 18 matching lines @@
         // We do not allow the arguments object to occur in a context where it
         // may escape, but assignments to stack-allocated locals are
         // permitted.
         CHECK_ALIVE(VisitForValue(expr->value(), ARGUMENTS_ALLOWED));
         HValue* value = Pop();
         Bind(var, value);
         return ast_context()->ReturnValue(value);
       }
 
       case Variable::CONTEXT: {
-        ASSERT(var->mode() != CONST);
         // Bail out if we try to mutate a parameter value in a function using
         // the arguments object.  We do not (yet) correctly handle the
         // arguments property of the function.
         if (info()->scope()->arguments() != NULL) {
           // Parameters will rewrite to context slots.  We have no direct way
           // to detect that the variable is a parameter.
           int count = info()->scope()->num_parameters();
           for (int i = 0; i < count; ++i) {
             if (var == info()->scope()->parameter(i)) {
               return Bailout("assignment to parameter in arguments object");
             }
           }
         }
 
         CHECK_ALIVE(VisitForValue(expr->value()));
-        HValue* context = BuildContextChainWalk(var);
         HStoreContextSlot::Mode mode;
         if (expr->op() == Token::ASSIGN) {
-          mode = (var->mode() == LET || var->mode() == CONST_HARMONY)
-              ? HStoreContextSlot::kAssignCheck : HStoreContextSlot::kAssign;
+          switch (var->mode()) {
+            case LET:
+              mode = HStoreContextSlot::kCheckDeoptimize;
+              break;
+            case CONST:
+              return ast_context()->ReturnValue(Pop());
+            case CONST_HARMONY:
+              UNREACHABLE();

[fschneider, 2011/12/13 16:15:00]

Also a short comment for the case here that this is already checked.

+            default:
+              mode = HStoreContextSlot::kNoCheck;
+          }
+        } else if (expr->op() == Token::INIT_VAR ||
+                   expr->op() == Token::INIT_LET ||
+                   expr->op() == Token::INIT_CONST_HARMONY) {
+          mode = HStoreContextSlot::kNoCheck;
         } else {
-          ASSERT(expr->op() == Token::INIT_VAR ||
-                 expr->op() == Token::INIT_LET ||
-                 expr->op() == Token::INIT_CONST_HARMONY);
-          mode = HStoreContextSlot::kAssign;
+          ASSERT(expr->op() == Token::INIT_CONST);
+
+          mode = HStoreContextSlot::kCheckIgnoreAssignment;
         }
+
+        HValue* context = BuildContextChainWalk(var);
         HStoreContextSlot* instr = new(zone()) HStoreContextSlot(
             context, var->index(), mode, Top());
         AddInstruction(instr);
         if (instr->HasObservableSideEffects()) {
           AddSimulate(expr->AssignmentId());
         }
         return ast_context()->ReturnValue(Pop());
       }
 
       case Variable::LOOKUP:
@@ skipping 1592 matching lines @@
           for (int i = 0; i < count; ++i) {
             if (var == info()->scope()->parameter(i)) {
               return Bailout("assignment to parameter in arguments object");
             }
           }
         }
 
         HValue* context = BuildContextChainWalk(var);
         HStoreContextSlot::Mode mode =
             (var->mode() == LET || var->mode() == CONST_HARMONY)
-            ? HStoreContextSlot::kAssignCheck : HStoreContextSlot::kAssign;
+            ? HStoreContextSlot::kCheckDeoptimize : HStoreContextSlot::kNoCheck;
         HStoreContextSlot* instr =
             new(zone()) HStoreContextSlot(context, var->index(), mode, after);
         AddInstruction(instr);
         if (instr->HasObservableSideEffects()) {
           AddSimulate(expr->AssignmentId());
         }
         break;
       }
 
       case Variable::LOOKUP:
@@ skipping 587 matching lines @@
         HValue* value = NULL;
         if (function != NULL) {
           VisitForValue(function);
           value = Pop();
         } else {
           value = graph()->GetConstantHole();
         }
         if (var->IsContextSlot()) {
           HValue* context = environment()->LookupContext();
           HStoreContextSlot* store = new HStoreContextSlot(
-              context, var->index(), HStoreContextSlot::kAssign, value);
+              context, var->index(), HStoreContextSlot::kNoCheck, value);
           AddInstruction(store);
           if (store->HasObservableSideEffects()) AddSimulate(proxy->id());
         } else {
           environment()->Bind(var, value);
         }
       }
       break;
     case Variable::LOOKUP:
       return Bailout("unsupported lookup slot in declaration");
   }
@@ skipping 1001 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal