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

src/full-codegen.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_FULL_CODEGEN_H_
 #define V8_FULL_CODEGEN_H_
 
 #include "src/v8.h"
 
 #include "src/allocation.h"
 #include "src/assert-scope.h"
 #include "src/ast.h"
 #include "src/bit-vector.h"
 #include "src/code-stubs.h"
 #include "src/codegen.h"
 #include "src/compiler.h"
 #include "src/globals.h"
 #include "src/objects.h"
 #include "src/scopes.h"
 
 namespace v8 {
 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.
 
 class FullCodeGenerator: public AstVisitor {
  public:
   enum State {
     NO_REGISTERS,
     TOS_REG
   };
 
@@ skipping 615 matching lines @@
   void CallIC(Handle<Code> code,
               TypeFeedbackId id = TypeFeedbackId::None());
 
   void CallLoadIC(ContextualMode mode, LanguageMode language_mode = SLOPPY,
                   TypeFeedbackId id = TypeFeedbackId::None());
   void CallGlobalLoadIC(Handle<String> name);
   void CallStoreIC(TypeFeedbackId id = TypeFeedbackId::None());
 
   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);
   void ExitTryBlock(int handler_index);
   void EnterFinallyBlock();
   void ExitFinallyBlock();
   void ClearPendingMessage();
 
   // Loop nesting counter.
   int loop_depth() { return loop_depth_; }
@@ skipping 394 matching lines @@
 
   Address start_;
   Address instruction_start_;
   uint32_t length_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FULL_CODEGEN_H_