Optimize loads from variables that might be shadowed by variables...

src/codegen-ia32.cc

 // Copyright 2006-2008 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 404 matching lines @@
       return frame_->Parameter(index);
 
     case Slot::LOCAL:
       return frame_->Local(index);
 
     case Slot::CONTEXT: {
       // Follow the context chain if necessary.
       ASSERT(!tmp.is(esi));  // do not overwrite context register
       Register context = esi;
       int chain_length = scope()->ContextChainLength(slot->var()->scope());
-      for (int i = chain_length; i-- > 0;) {
+      for (int i = 0; i < chain_length; i++) {
         // Load the closure.
         // (All contexts, even 'with' contexts, have a closure,
         // and it is the same for all contexts inside a function.
         // There is no need to go to the function context first.)
         __ mov(tmp, ContextOperand(context, Context::CLOSURE_INDEX));
         // Load the function context (which is the incoming, outer context).
         __ mov(tmp, FieldOperand(tmp, JSFunction::kContextOffset));
         context = tmp;
       }
       // We may have a 'with' context now. Get the function context.
       // (In fact this mov may never be the needed, since the scope analysis
       // may not permit a direct context access in this case and thus we are
       // always at a function context. However it is safe to dereference be-
       // cause the function context of a function context is itself. Before
       // deleting this mov we should try to create a counter-example first,
       // though...)
       __ mov(tmp, ContextOperand(context, Context::FCONTEXT_INDEX));
       return ContextOperand(tmp, index);
     }
 
     default:
       UNREACHABLE();
       return Operand(eax);
   }
 }
 
 
+Operand CodeGenerator::ContextSlotOperandCheckExtensions(Slot* slot,
+                                                         Register tmp,
+                                                         Label* slow) {
+  ASSERT(slot->type() == Slot::CONTEXT);
+  int index = slot->index();
+  __ mov(tmp, Operand(esi));
+  for (Scope* s = scope(); s != slot->var()->scope(); s = s->outer_scope()) {
+    if (s->num_heap_slots() > 0) {
+      if (s->calls_eval()) {
+        // Check that extension is NULL.
+        __ cmp(ContextOperand(tmp, Context::EXTENSION_INDEX), Immediate(0));
+        __ j(not_equal, slow, not_taken);
+      }
+      __ mov(tmp, ContextOperand(tmp, Context::CLOSURE_INDEX));
+      __ mov(tmp, FieldOperand(tmp, JSFunction::kContextOffset));
+    }
+  }
+  // Check that last extension is NULL.
+  __ cmp(ContextOperand(tmp, Context::EXTENSION_INDEX), Immediate(0));
+  __ j(not_equal, slow, not_taken);
+  __ mov(tmp, ContextOperand(tmp, Context::FCONTEXT_INDEX));
+  return ContextOperand(tmp, index);
+}
+
+
+
 // Loads a value on TOS. If it is a boolean value, the result may have been
 // (partially) translated into branches, or it may have set the condition
 // code register. If force_cc is set, the value is forced to set the
 // condition code register and no value is pushed. If the condition code
 // register was set, has_cc() is true and cc_reg_ contains the condition to
 // test for 'true'.
 void CodeGenerator::LoadCondition(Expression* x,
                                   TypeofState typeof_state,
                                   Label* true_target,
                                   Label* false_target,
@@ skipping 934 matching lines @@
   Variable* var = node->proxy()->var();
   ASSERT(var != NULL);  // must have been resolved
   Slot* slot = var->slot();
 
   // 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.
   if (slot != NULL && slot->type() == Slot::LOOKUP) {
     // Variables with a "LOOKUP" slot were introduced as non-locals
     // during variable resolution and must have mode DYNAMIC.
-    ASSERT(var->mode() == Variable::DYNAMIC);
+    ASSERT(var->is_dynamic());
     // For now, just do a runtime call.
     frame_->Push(esi);
     frame_->Push(Immediate(var->name()));
     // Declaration nodes are always introduced in one of two modes.
     ASSERT(node->mode() == Variable::VAR || node->mode() == Variable::CONST);
     PropertyAttributes attr = node->mode() == Variable::VAR ? NONE : READ_ONLY;
     frame_->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
@@ skipping 898 matching lines @@
   Load(node->then_expression(), typeof_state());
   __ jmp(&exit);
   __ bind(&else_);
   Load(node->else_expression(), typeof_state());
   __ bind(&exit);
 }
 
 
 void CodeGenerator::LoadFromSlot(Slot* slot, TypeofState typeof_state) {
   if (slot->type() == Slot::LOOKUP) {
-    ASSERT(slot->var()->mode() == Variable::DYNAMIC);
+    ASSERT(slot->var()->is_dynamic());
 
-    // For now, just do a runtime call.
+    Label slow, done;
+
+    // Generate fast-case code for variables that might be shadowed by
+    // eval-introduced variables.  Eval is used a lot without
+    // introducing variables.  In those cases, we do not want to
+    // perform a runtime call for all variables in the scope
+    // containing the eval.
+    if (slot->var()->mode() == Variable::DYNAMIC_GLOBAL) {
+      LoadFromGlobalSlotCheckExtensions(slot, typeof_state, ebx, &slow);
+      __ jmp(&done);
+
+    } else if (slot->var()->mode() == Variable::DYNAMIC_LOCAL) {
+      Slot* potential_slot = slot->var()->local_if_not_shadowed()->slot();
+      __ mov(eax,
+             ContextSlotOperandCheckExtensions(potential_slot,
+                                               ebx,
+                                               &slow));
+      __ jmp(&done);
+    }
+
+    __ bind(&slow);
     frame_->Push(esi);
     frame_->Push(Immediate(slot->var()->name()));
-
     if (typeof_state == INSIDE_TYPEOF) {
       __ CallRuntime(Runtime::kLoadContextSlotNoReferenceError, 2);
     } else {
       __ CallRuntime(Runtime::kLoadContextSlot, 2);
     }
+
+    __ bind(&done);
     frame_->Push(eax);
 
   } else {
     // Note: We would like to keep the assert below, but it fires because of
     // some nasty code in LoadTypeofExpression() which should be removed...
-    // ASSERT(slot->var()->mode() != Variable::DYNAMIC);
+    // ASSERT(!slot->var()->is_dynamic());
     if (slot->var()->mode() == Variable::CONST) {
       // Const slots may contain 'the hole' value (the constant hasn't been
       // initialized yet) which needs to be converted into the 'undefined'
       // value.
       Comment cmnt(masm_, "[ Load const");
       Label exit;
       __ mov(eax, SlotOperand(slot, ecx));
       __ cmp(eax, Factory::the_hole_value());
       __ j(not_equal, &exit);
       __ mov(eax, Factory::undefined_value());
       __ bind(&exit);
       frame_->Push(eax);
     } else {
       frame_->Push(SlotOperand(slot, ecx));
     }
   }
 }
 
 
+void CodeGenerator::LoadFromGlobalSlotCheckExtensions(Slot* slot,
+                                                      TypeofState typeof_state,
+                                                      Register tmp,
+                                                      Label* slow) {
+  // Check that no extension objects have been created by calls to
+  // eval from the current scope to the global scope.
+  __ mov(tmp, Operand(esi));
+  for (Scope* s = scope(); s != NULL; s = s->outer_scope()) {
+    if (s->num_heap_slots() > 0) {
+      if (s->calls_eval()) {
+        // Check that extension is NULL.
+        __ cmp(ContextOperand(tmp, Context::EXTENSION_INDEX), Immediate(0));
+        __ j(not_equal, slow, not_taken);
+      }
+      // Load next context in chain.
+      __ mov(tmp, ContextOperand(tmp, Context::CLOSURE_INDEX));
+      __ mov(tmp, FieldOperand(tmp, JSFunction::kContextOffset));
+    }
+    // If no outer scope calls eval, we do not need to check more
+    // context extensions.
+    if (!s->outer_scope_calls_eval()) break;
+  }
+
+  // All extension objects were empty and it is safe to use a global
+  // load IC call.
+  Handle<Code> ic(Builtins::builtin(Builtins::LoadIC_Initialize));
+  // Load the global object.
+  LoadGlobal();
+  // Setup the name register.
+  __ mov(ecx, slot->var()->name());
+  // Call IC stub.
+  if (typeof_state == INSIDE_TYPEOF) {
+    __ call(ic, RelocInfo::CODE_TARGET);
+  } else {
+    __ call(ic, RelocInfo::CODE_TARGET_CONTEXT);
+  }
+
+  // Pop the global object. The result is in eax.
+  frame_->Pop();
+}
+
+
 void CodeGenerator::VisitSlot(Slot* node) {
   Comment cmnt(masm_, "[ Slot");
   LoadFromSlot(node, typeof_state());
 }
 
 
 void CodeGenerator::VisitVariableProxy(VariableProxy* node) {
   Comment cmnt(masm_, "[ VariableProxy");
   Variable* var = node->var();
   Expression* expr = var->rewrite();
@@ skipping 1634 matching lines @@
   ASSERT(!is_illegal());
   ASSERT(!cgen_->has_cc());
   MacroAssembler* masm = cgen_->masm();
   VirtualFrame* frame = cgen_->frame();
   switch (type_) {
     case SLOT: {
       Comment cmnt(masm, "[ Store to Slot");
       Slot* slot = expression_->AsVariableProxy()->AsVariable()->slot();
       ASSERT(slot != NULL);
       if (slot->type() == Slot::LOOKUP) {
-        ASSERT(slot->var()->mode() == Variable::DYNAMIC);
+        ASSERT(slot->var()->is_dynamic());
 
         // For now, just do a runtime call.
         frame->Push(esi);
         frame->Push(Immediate(slot->var()->name()));
 
         if (init_state == CONST_INIT) {
           // Same as the case for a normal store, but ignores attribute
           // (e.g. READ_ONLY) of context slot so that we can initialize
           // const properties (introduced via eval("const foo = (some
           // expr);")). Also, uses the current function context instead of
@@ skipping 11 matching lines @@
           __ CallRuntime(Runtime::kInitializeConstContextSlot, 3);
         } else {
           __ CallRuntime(Runtime::kStoreContextSlot, 3);
         }
         // Storing a variable must keep the (new) value on the expression
         // stack. This is necessary for compiling chained assignment
         // expressions.
         frame->Push(eax);
 
       } else {
-        ASSERT(slot->var()->mode() != Variable::DYNAMIC);
+        ASSERT(!slot->var()->is_dynamic());
 
         Label exit;
         if (init_state == CONST_INIT) {
           ASSERT(slot->var()->mode() == Variable::CONST);
           // Only the first const initialization must be executed (the slot
           // still contains 'the hole' value). When the assignment is
           // executed, the code is identical to a normal store (see below).
           Comment cmnt(masm, "[ Init const");
           __ mov(eax, cgen_->SlotOperand(slot, ecx));
           __ cmp(eax, Factory::the_hole_value());
@@ skipping 1272 matching lines @@
 
   // Slow-case: Go through the JavaScript implementation.
   __ bind(&slow);
   __ InvokeBuiltin(Builtins::INSTANCE_OF, JUMP_FUNCTION);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal