[inspector] cache stack frame for call sites

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index f12b84813bc01257393af7fdeb54435496eaf343..55d6738e1001105639a3518d8ad9c8d7a27da6e6 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -625,6 +625,20 @@ class CaptureStackTraceHelper {
 
   Handle<StackFrameInfo> NewStackFrameObject(
       const FrameSummary::JavaScriptFrameSummary& summ) {
+    int code_offset = summ.code_offset();
+    Handle<AbstractCode> code = summ.abstract_code();
+    Object* maybe_cache = code->stack_frame_cache();
+    Handle<UnseededNumberDictionary> cache;
+    if (maybe_cache->IsUnseededNumberDictionary()) {
+      cache = handle(UnseededNumberDictionary::cast(maybe_cache));
+    } else {
+      cache = UnseededNumberDictionary::NewEmpty(isolate_);
+      code->set_stack_frame_cache(*cache);
+    }
+    int entry = cache->FindEntry(code_offset);
+    if (entry != UnseededNumberDictionary::kNotFound) {
+      return handle(StackFrameInfo::cast(cache->ValueAt(entry)), isolate_);
+    }

[rmcilroy, 2017/04/04 09:22:49]

Rather than requiring a new field in both code and bytecode objects (which are
quite common, so this is a not insignificant memory overhead) could we instead
build a side hash-table cache keyed by the code object or some other indicator
of the call site? (Then this would only be an overhead when code generates stack
frames. 

[Yang, 2017/04/04 13:51:58]

+1 for a side table. If you use code objects as hash table key, you will need to
extend GetSimpleHash to also handle Code* and BytecodeArray*.

Actually I think using the source position table as key would make more sense.
You could use its content to compute the hash.

[kozy, 2017/04/04 19:11:07]

Done.

[kozy, 2017/04/04 19:11:07]

Done.

     Handle<StackFrameInfo> frame = factory()->NewStackFrameInfo();
     Handle<Script> script = Handle<Script>::cast(summ.script());
     if (options_ & StackTrace::kLineNumber) {
@@ -657,6 +671,9 @@ class CaptureStackTraceHelper {
     if (options_ & StackTrace::kIsConstructor) {
       frame->set_is_constructor(summ.is_constructor());
     }
+    auto new_cache =
+        UnseededNumberDictionary::AtNumberPut(cache, code_offset, frame);
+    if (*new_cache != *cache) code->set_stack_frame_cache(*new_cache);
     return frame;
   }