expand DIContext interface a bit

[david2050]

Summary

This allows a bit more control for scenarios where client might
modifiy a DIContext

[twoh]

Can you please provide a bit more context about when the client might want this function?

[david2050]

The first change is simply performance related.
The second allows a client to incrementally build a vector, using the getMutableFrame method to access individual frames

[Kader]

LGTM :)

[Kader]

LGTM

llvm/trunk/include/llvm/DebugInfo/DIContext.h

 
 /// A format-neutral container for inlined code description.
 class DIInliningInfo {
   SmallVector<DILineInfo, 4> Frames;
 
 public:
   DIInliningInfo() = default;
 
-  DILineInfo getFrame(unsigned Index) const {
+  const DILineInfo & getFrame(unsigned Index) const {
     assert(Index < Frames.size());
     return Frames[Index];
   }
 
   DILineInfo *getMutableFrame(unsigned Index) {
     assert(Index < Frames.size());
     return &Frames[Index];
   }
 
   uint32_t getNumberOfFrames() const {
     return Frames.size();
   }
 
   void addFrame(const DILineInfo &Frame) {
     Frames.push_back(Frame);
   }
+  
+  void resize(unsigned i) {
+    Frames.resize(i);
+  }
+  
 };
 
 /// Container for description of a global variable.
 struct DIGlobal {
   std::string Name;
   uint64_t Start = 0;
   uint64_t Size = 0;