[Sampling Heap Profiler] Tolerate unmaterialized closure during deopt

Samples taken during deoptimization require care in the stack walk
used to gather frames. The top N stack frames may not have JSFunction
objects in place, because those frames represent inlined functions
which may not have closures yet.

Bug: v8:7314
Change-Id: Ib6488aee46a47d5341cab1b1c9c3851592ba6509
Reviewed-on: https://chromium-review.googlesource.com/870036
Commit-Queue: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ali Ijaz Sheikh <ofrobots@google.com>
Cr-Commit-Position: refs/heads/master@{#50732}

src/frames.cc

@@ -1023,6 +1023,15 @@ JSFunction* JavaScriptFrame::function() const {
   return JSFunction::cast(function_slot_object());
 }
 
+Object* JavaScriptFrame::unchecked_function() const {
+  // During deoptimization of an optimized function, we may have yet to
+  // materialize some closures on the stack. The arguments marker object
+  // marks this case.
+  DCHECK(function_slot_object()->IsJSFunction() ||
+         isolate()->heap()->arguments_marker() == function_slot_object());
+  return function_slot_object();
+}
+
 Object* JavaScriptFrame::receiver() const { return GetParameter(-1); }
 
 Object* JavaScriptFrame::context() const {

src/frames.h

@@ -704,6 +704,7 @@ class JavaScriptFrame : public StandardFrame {
 
   // Accessors.
   virtual JSFunction* function() const;
+  Object* unchecked_function() const;
   Object* receiver() const override;
   Object* context() const override;
   Script* script() const override;

src/profiler/sampling-heap-profiler.cc

@@ -150,10 +150,16 @@ SamplingHeapProfiler::AllocationNode* SamplingHeapProfiler::AddStack() {
   int frames_captured = 0;
   while (!it.done() && frames_captured < stack_depth_) {
     JavaScriptFrame* frame = it.frame();
+    // If we are materializing objects during deoptimization, inlined
+    // closures may not yet be materialized, and this includes the
+    // closure on the stack. Skip over any such frames (they'll be
+    // in the top frames of the stack). The allocations made in this
+    // sensitive moment belong to the formerly optimized frame anyway.
+    if (frame->unchecked_function()->IsJSFunction()) {
       SharedFunctionInfo* shared = frame->function()->shared();
       stack.push_back(shared);
-
       frames_captured++;
+    }
     it.Advance();
   }