[DebugInfo] don't make an MDTuple just to leak it

[vtjnash]

Summary

There does not seem to be any purpose to allocating this object, which
is Metadata, so LLVM will simply leak it until the context is destroyed
(the subprogram metadata it contains are distinct, so there is little
chance of it being reused later). This should not have a functional
change.

This seems to be left over from an earlier design, when it used to call

CUNode->replaceSubprograms(SPs.get());

here also. (removed in http://reviews.llvm.org/D19034)

[aprantl]

Nice find.

llvm/include/llvm/IR/DIBuilder.h

class DIBuilder {
     Function *DeclareFn;     ///< llvm.dbg.declare
     Function *ValueFn;       ///< llvm.dbg.value
     Function *LabelFn;       ///< llvm.dbg.label
     Function *AssignFn;      ///< llvm.dbg.assign
 
     SmallVector<TrackingMDNodeRef, 4> AllEnumTypes;
     /// Track the RetainTypes, since they can be updated later on.
     SmallVector<TrackingMDNodeRef, 4> AllRetainTypes;
-    SmallVector<Metadata *, 4> AllSubprograms;
+    SmallVector<DISubprogram *, 4> AllSubprograms;
     SmallVector<Metadata *, 4> AllGVs;
     SmallVector<TrackingMDNodeRef, 4> AllImportedModules;
     /// Map Macro parent (which can be DIMacroFile or nullptr) to a list of
     /// Metadata all of type DIMacroNode.
     /// DIMacroNode's with nullptr parent are DICompileUnit direct children.
     MapVector<MDNode *, SetVector<Metadata *>> AllMacrosPerParent;
 
     /// Track nodes that may be unresolved.

llvm/lib/IR/DIBuilder.cpp

void DIBuilder::finalize() {
   SmallPtrSet<Metadata *, 16> RetainSet;
   for (unsigned I = 0, E = AllRetainTypes.size(); I < E; I++)
     if (RetainSet.insert(AllRetainTypes[I]).second)
       RetainValues.push_back(AllRetainTypes[I]);
 
   if (!RetainValues.empty())
     CUNode->replaceRetainedTypes(MDTuple::get(VMContext, RetainValues));
 
-  DISubprogramArray SPs = MDTuple::get(VMContext, AllSubprograms);
-  for (auto *SP : SPs)
+  for (auto *SP : AllSubprograms)
     finalizeSubprogram(SP);
   for (auto *N : RetainValues)
     if (auto *SP = dyn_cast<DISubprogram>(N))
       finalizeSubprogram(SP);
 
   if (!AllGVs.empty())
     CUNode->replaceGlobalVariables(MDTuple::get(VMContext, AllGVs));