Do not visit slots in the top-level code generator's backend.

Slots appear only indirectly in the AST (through variables linked to
variable proxies).  Slots are shared among variable references, so
putting compilation-time state on them is potentially a source of
bugs.  Avoid it for now.

Review URL: http://codereview.chromium.org/284009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3079 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/fast-codegen-arm.cc

@@ -125,14 +125,21 @@ void FastCodeGenerator::VisitReturnStatement(ReturnStatement* stmt) {
 }
 
 
-void FastCodeGenerator::VisitSlot(Slot* expr) {
-  Comment cmnt(masm_, "[ Slot");
+void FastCodeGenerator::VisitVariableProxy(VariableProxy* expr) {
+  Comment cmnt(masm_, "[ VariableProxy");
+  Expression* rewrite = expr->var()->rewrite();
+  ASSERT(rewrite != NULL);
+
+  Slot* slot = rewrite->AsSlot();
+  ASSERT(slot != NULL);
+  { Comment cmnt(masm_, "[ Slot");
     if (expr->location().is_temporary()) {
-    __ ldr(ip, MemOperand(fp, SlotOffset(expr)));
+      __ ldr(ip, MemOperand(fp, SlotOffset(slot)));
       __ push(ip);
     } else {
       ASSERT(expr->location().is_nowhere());
     }
+  }
 }
 
 

src/fast-codegen.cc

@@ -190,14 +190,9 @@ void FastCodeGenerator::VisitConditional(Conditional* expr) {
 }
 
 
-void FastCodeGenerator::VisitVariableProxy(VariableProxy* expr) {
-  Comment cmnt(masm_, "[ VariableProxy");
-  Expression* rewrite = expr->var()->rewrite();
-  ASSERT(rewrite != NULL);
-
-  // Forward to the proxy's rewrite.
-  rewrite->set_location(expr->location());
-  Visit(rewrite);
+void FastCodeGenerator::VisitSlot(Slot* expr) {
+  // Slots do not appear directly in the AST.
+  UNREACHABLE();
 }
 
 

src/ia32/fast-codegen-ia32.cc

@@ -115,13 +115,20 @@ void FastCodeGenerator::VisitReturnStatement(ReturnStatement* stmt) {
 }
 
 
-void FastCodeGenerator::VisitSlot(Slot* expr) {
-  Comment cmnt(masm_, "[ Slot");
+void FastCodeGenerator::VisitVariableProxy(VariableProxy* expr) {
+  Comment cmnt(masm_, "[ VariableProxy");
+  Expression* rewrite = expr->var()->rewrite();
+  ASSERT(rewrite != NULL);
+
+  Slot* slot = rewrite->AsSlot();
+  ASSERT(slot != NULL);
+  { Comment cmnt(masm_, "[ Slot");
     if (expr->location().is_temporary()) {
-    __ push(Operand(ebp, SlotOffset(expr)));
+      __ push(Operand(ebp, SlotOffset(slot)));
     } else {
       ASSERT(expr->location().is_nowhere());
     }
+  }
 }
 
 

src/x64/fast-codegen-x64.cc

@@ -132,13 +132,20 @@ void FastCodeGenerator::VisitReturnStatement(ReturnStatement* stmt) {
 }
 
 
-void FastCodeGenerator::VisitSlot(Slot* expr) {
-  Comment cmnt(masm_, "[ Slot");
+void FastCodeGenerator::VisitVariableProxy(VariableProxy* expr) {
+  Comment cmnt(masm_, "[ VariableProxy");
+  Expression* rewrite = expr->var()->rewrite();
+  ASSERT(rewrite != NULL);
+
+  Slot* slot = rewrite->AsSlot();
+  ASSERT(slot != NULL);
+  { Comment cmnt(masm_, "[ Slot");
     if (expr->location().is_temporary()) {
-    __ push(Operand(rbp, SlotOffset(expr)));
+      __ push(Operand(rbp, SlotOffset(slot)));
     } else {
       ASSERT(expr->location().is_nowhere());
     }
+  }
 }