Merge pull request #8301 from jimingham/dont-count-frames

Don't count all the frames just to skip the current inlined ones. (#8…

Author: jimingham

lldb/include/lldb/Target/Thread.h

@@ -391,6 +391,13 @@ class Thread : public std::enable_shared_from_this<Thread>,
   /// and having the thread call the SystemRuntime again.
   virtual bool ThreadHasQueueInformation() const { return false; }
 
+  /// GetStackFrameCount can be expensive.  Stacks can get very deep, and they
+  /// require memory reads for each frame.  So only use GetStackFrameCount when 
+  /// you need to know the depth of the stack.  When iterating over frames, its
+  /// better to generate the frames one by one with GetFrameAtIndex, and when
+  /// that returns NULL, you are at the end of the stack.  That way your loop
+  /// will only do the work it needs to, without forcing lldb to realize
+  /// StackFrames you weren't going to look at.
   virtual uint32_t GetStackFrameCount() {
     return GetStackFrameList()->GetNumFrames();
   }

lldb/source/Expression/DWARFExpression.cpp

@@ -613,11 +613,10 @@ static bool Evaluate_DW_OP_entry_value(std::vector<Value> &stack,
   StackFrameSP parent_frame = nullptr;
   addr_t return_pc = LLDB_INVALID_ADDRESS;
   uint32_t current_frame_idx = current_frame->GetFrameIndex();
-  uint32_t num_frames = thread->GetStackFrameCount();
-  for (uint32_t parent_frame_idx = current_frame_idx + 1;
-       parent_frame_idx < num_frames; ++parent_frame_idx) {
+
+  for (uint32_t parent_frame_idx = current_frame_idx + 1;;parent_frame_idx++) {
     parent_frame = thread->GetStackFrameAtIndex(parent_frame_idx);
-    // Require a valid sequence of frames.
+    // If this is null, we're at the end of the stack.
     if (!parent_frame)
       break;