Debugger: use debug break slots instead of ICs (except for calls).

src/full-codegen.h

Index: src/full-codegen.h
diff --git a/src/full-codegen.h b/src/full-codegen.h
index ac74407e3f71fc80910eb8c30ae5c4dfb6884be1..d420cf7c0454ec74bfd5b45010cc0404a6317b02 100644
--- a/src/full-codegen.h
+++ b/src/full-codegen.h
@@ -24,35 +24,6 @@ namespace internal {
 // Forward declarations.
 class JumpPatchSite;
 
-// AST node visitor which can tell whether a given statement will be breakable
-// when the code is compiled by the full compiler in the debugger. This means
-// that there will be an IC (load/store/call) in the code generated for the
-// debugger to piggybag on.
-class BreakableStatementChecker: public AstVisitor {
- public:
-  BreakableStatementChecker(Isolate* isolate, Zone* zone)
-      : is_breakable_(false) {
-    InitializeAstVisitor(isolate, zone);
-  }
-
-  void Check(Statement* stmt);
-  void Check(Expression* stmt);
-
-  bool is_breakable() { return is_breakable_; }
-
- private:
-  // AST node visit functions.
-#define DECLARE_VISIT(type) virtual void Visit##type(type* node) override;
-  AST_NODE_LIST(DECLARE_VISIT)
-#undef DECLARE_VISIT
-
-  bool is_breakable_;
-
-  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
-  DISALLOW_COPY_AND_ASSIGN(BreakableStatementChecker);
-};
-
-
 // -----------------------------------------------------------------------------
 // Full code generator.
 
@@ -688,9 +659,18 @@ class FullCodeGenerator: public AstVisitor {
 
   void SetFunctionPosition(FunctionLiteral* fun);
   void SetReturnPosition(FunctionLiteral* fun);
-  void SetStatementPosition(Statement* stmt);
-  void SetExpressionPosition(Expression* expr);
-  void SetSourcePosition(int pos);
+
+  enum InsertBreak { INSERT_BREAK, SKIP_BREAK };
+
+  void SetStatementPosition(Statement* stmt,

[ulan, 2015/07/06 09:24:19]

Can we make the insert_break explicit in SetStatementPosition and
SetExpressionPosition?

Since they are using opposite defaults call-sites become confusing. Also
SetReturnPosition and SetFunctionPosition do not record slots at all, but
SetExpressionAsStatementPosition does.

SetExpressionAsStatementPosition should be named
SetExpressionAsStatementPositionAndInsertBreak.

[Yang, 2015/07/06 10:05:08]

The background here is that we generally break at statements, but not at
expressions. Expression positions are mostly just used for stack traces, not
break points.

That's why the default is that statement --> break, expression --> no break. Not
having the default would mean that I would have to add a lot of boilerplate at
all call sites except for a few exceptions.

Can I simply add a comment here?

+                            InsertBreak insert_break = INSERT_BREAK);
+
+  void SetExpressionPosition(Expression* expr,
+                             InsertBreak insert_break = SKIP_BREAK);
+
+  // Emit statement position for an expression. Used in loop headers where we
+  // want to be able to break at the header for each iteration.
+  void SetExpressionAsStatementPosition(Expression* expr);
 
   // Non-local control flow support.
   void EnterTryBlock(int handler_index, Label* handler);