[debug] correctly get arg count for optimized builtin frames.

R=jgruber@chromium.org

Bug: v8:178
Change-Id: Ie2279c8a1bb50d01186dbd9dd29145bca9aeaf6f
Reviewed-on: https://chromium-review.googlesource.com/972983
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52106}

src/frames.cc

@@ -1014,10 +1014,18 @@ Code* JavaScriptFrame::unchecked_code() const {
 int JavaScriptFrame::GetNumberOfIncomingArguments() const {
   DCHECK(can_access_heap_objects() &&
          isolate()->heap()->gc_state() == Heap::NOT_IN_GC);
-
   return function()->shared()->internal_formal_parameter_count();
 }
 
+int OptimizedFrame::GetNumberOfIncomingArguments() const {
+  Code* code = LookupCode();
+  if (code->kind() == Code::BUILTIN) {
+    return static_cast<int>(
+        Memory::intptr_at(fp() + OptimizedBuiltinFrameConstants::kArgCOffset));
+  } else {
+    return JavaScriptFrame::GetNumberOfIncomingArguments();
+  }
+}
 
 Address JavaScriptFrame::GetCallerStackPointer() const {
   return fp() + StandardFrameConstants::kCallerSPOffset;

src/frames.h

@@ -848,6 +848,8 @@ class OptimizedFrame : public JavaScriptFrame {
  protected:
   inline explicit OptimizedFrame(StackFrameIteratorBase* iterator);
 
+  int GetNumberOfIncomingArguments() const override;
+
  private:
   friend class StackFrameIteratorBase;
 

test/cctest/test-debug.cc

@@ -1569,6 +1569,42 @@ TEST(BreakPointConditionBuiltin) {
   ExpectString("f(10)", "aaaaaaaaaaaaaaaaaaaa");
   CHECK_EQ(1, break_point_hit_count);
 
+  // === Test var-arg builtins ===
+  break_point_hit_count = 0;
+  builtin = CompileRun("String.fromCharCode").As<v8::Function>();
+  CompileRun("function f() { return String.fromCharCode(1, 2, 3); }");
+  CHECK_EQ(0, break_point_hit_count);
+
+  // Run with breakpoint.
+  bp = SetBreakPoint(builtin, 0, "arguments.length == 3 && arguments[1] == 2");
+  CompileRun("f(1, 2, 3)");
+  CHECK_EQ(1, break_point_hit_count);
+
+  // Run without breakpoints.
+  ClearBreakPoint(bp);
+  CompileRun("f(1, 2, 3)");
+  CHECK_EQ(1, break_point_hit_count);
+
+  // === Test rest arguments ===
+  break_point_hit_count = 0;
+  builtin = CompileRun("String.fromCharCode").As<v8::Function>();
+  CompileRun("function f(...args) { return String.fromCharCode(...args); }");
+  CHECK_EQ(0, break_point_hit_count);
+
+  // Run with breakpoint.
+  bp = SetBreakPoint(builtin, 0, "arguments.length == 3 && arguments[1] == 2");
+  CompileRun("f(1, 2, 3)");
+  CHECK_EQ(1, break_point_hit_count);
+
+  ClearBreakPoint(bp);
+  CompileRun("f(1, 3, 3)");
+  CHECK_EQ(1, break_point_hit_count);
+
+  // Run without breakpoints.
+  ClearBreakPoint(bp);
+  CompileRun("f(1, 2, 3)");
+  CHECK_EQ(1, break_point_hit_count);
+
   // === Test receiver ===
   break_point_hit_count = 0;
   builtin = CompileRun("String.prototype.repeat").As<v8::Function>();