More precise break points and stepping when debugging...

src/ia32/assembler-ia32.cc

Index: src/ia32/assembler-ia32.cc
===================================================================
--- src/ia32/assembler-ia32.cc	(revision 4816)
+++ src/ia32/assembler-ia32.cc	(working copy)
@@ -206,6 +206,7 @@
             patcher.masm()->SizeOfCodeGeneratedSince(&check_codesize));
 
   // Add the requested number of int3 instructions after the call.
+  ASSERT_GE(guard_bytes, 0);
   for (int i = 0; i < guard_bytes; i++) {
     patcher.masm()->int3();
   }
@@ -2371,6 +2372,13 @@
 }
 
 
+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);
@@ -2393,13 +2401,16 @@
 }
 
 
-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
@@ -2409,7 +2420,11 @@
     EnsureSpace ensure_space(this);
     RecordRelocInfo(RelocInfo::POSITION, current_position_);
     written_position_ = current_position_;
+    written = true;
   }
+
+  // Return whether something was written.
+  return written;
 }