More precise break points and stepping when debugging...

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
===================================================================
--- src/x64/assembler-x64.cc	(revision 4816)
+++ src/x64/assembler-x64.cc	(working copy)
@@ -2800,6 +2800,13 @@
 }
 
 
+void Assembler::RecordDebugBreakSlot() {
+  WriteRecordedPositions();
+  EnsureSpace ensure_space(this);
+  RecordRelocInfo(RelocInfo::DEBUG_BREAK_SLOT);
+}
+
+
 void Assembler::RecordComment(const char* msg) {
   if (FLAG_debug_code) {
     EnsureSpace ensure_space(this);
@@ -2822,13 +2829,16 @@
 }
 
 
-void Assembler::WriteRecordedPositions() {
+bool Assembler::WriteRecordedPositions() {
+  bool written = false;
+
   // Write the statement position if it is different from what was written last
   // time.
   if (current_statement_position_ != written_statement_position_) {
     EnsureSpace ensure_space(this);
     RecordRelocInfo(RelocInfo::STATEMENT_POSITION, current_statement_position_);
     written_statement_position_ = current_statement_position_;
+    written = true;
   }
 
   // Write the position if it is different from what was written last time and
@@ -2838,7 +2848,11 @@
     EnsureSpace ensure_space(this);
     RecordRelocInfo(RelocInfo::POSITION, current_position_);
     written_position_ = current_position_;
+    written = true;
   }
+
+  // Return whether something was written.
+  return written;
 }