[interpreter, debugger] support debug breaks via bytecode array copy

src/x64/builtins-x64.cc

Index: src/x64/builtins-x64.cc
diff --git a/src/x64/builtins-x64.cc b/src/x64/builtins-x64.cc
index 98f253838c55315c21af8efff93a1f6d3e1c5c53..391fbafb157b261a2f53f863308b6f2f400ba40a 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -494,8 +494,14 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
   // Get the bytecode array from the function object and load the pointer to the
   // first entry into edi (InterpreterBytecodeRegister).
   __ movp(rax, FieldOperand(rdi, JSFunction::kSharedFunctionInfoOffset));
+
+  Label load_debug_bytecode_array, bytecode_array_loaded;
+  __ cmpp(FieldOperand(rax, SharedFunctionInfo::kDebugInfoOffset),
+          Immediate(DebugInfo::uninitialized()));
+  __ j(not_equal, &load_debug_bytecode_array);
   __ movp(kInterpreterBytecodeArrayRegister,
           FieldOperand(rax, SharedFunctionInfo::kFunctionDataOffset));
+  __ bind(&bytecode_array_loaded);
 
   if (FLAG_debug_code) {
     // Check function data field is actually a BytecodeArray object.
@@ -569,6 +575,14 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
 
   // Even though the first bytecode handler was called, we will never return.
   __ Abort(kUnexpectedReturnFromBytecodeHandler);
+
+  // Load debug copy of the bytecode array.
+  __ bind(&load_debug_bytecode_array);
+  Register debug_info = kInterpreterBytecodeArrayRegister;
+  __ movp(debug_info, FieldOperand(rax, SharedFunctionInfo::kDebugInfoOffset));
+  __ movp(kInterpreterBytecodeArrayRegister,
+          FieldOperand(debug_info, DebugInfo::kAbstractCodeIndex));
+  __ jmp(&bytecode_array_loaded);
 }