IR: Use std::vector instead of SmallPtrSet for distinct nodes, NFC

We never use the set-ness of SmallPtrSet for distinct nodes.  Eventually
we may start garbage-collecting or reference-counting nodes (in which
cases we'd want to remove things from this collection, and a fast erase
would be valuable), but in the meantime a vector is sufficient.

llvm-svn: 266835

llvm/lib/IR/LLVMContextImpl.h

@@ -33,6 +33,7 @@
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Support/Dwarf.h"
+#include <vector>
 
 namespace llvm {
 
@@ -1026,9 +1027,9 @@ public:
 
   // MDNodes may be uniqued or not uniqued.  When they're not uniqued, they
   // aren't in the MDNodeSet, but they're still shared between objects, so no
-  // one object can destroy them.  This set allows us to at least destroy them
-  // on Context destruction.
-  SmallPtrSet<MDNode *, 1> DistinctMDNodes;
+  // one object can destroy them.  Keep track of them here so we can delete
+  // them on context teardown.
+  std::vector<MDNode *> DistinctMDNodes;
 
   DenseMap<Type*, ConstantAggregateZero*> CAZConstants;
 

llvm/lib/IR/Metadata.cpp

@@ -806,7 +806,7 @@ void MDNode::storeDistinctInContext() {
 #include "llvm/IR/Metadata.def"
   }
 
-  getContext().pImpl->DistinctMDNodes.insert(this);
+  getContext().pImpl->DistinctMDNodes.push_back(this);
 }
 
 void MDNode::replaceOperandWith(unsigned I, Metadata *New) {