Update SetVector to rely on the underlying set's insert to return a pair<iterator, bool>

This is to be consistent with StringSet and ultimately with the standard
library's associative container insert function.

This lead to updating SmallSet::insert to return pair<iterator, bool>,
and then to update SmallPtrSet::insert to return pair<iterator, bool>,
and then to update all the existing users of those functions...

llvm-svn: 222334
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index a610e57..79109b7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -615,7 +615,7 @@
     SDNode *N = Worklist.pop_back_val();
 
     // If we've already seen this node, ignore it.
-    if (!VisitedNodes.insert(N))
+    if (!VisitedNodes.insert(N).second)
       continue;
 
     // Otherwise, add all chain operands to the worklist.
@@ -1741,7 +1741,7 @@
 
   // Don't revisit nodes if we already scanned it and didn't fail, we know we
   // won't fail if we scan it again.
-  if (!Visited.insert(Use))
+  if (!Visited.insert(Use).second)
     return false;
 
   for (unsigned i = 0, e = Use->getNumOperands(); i != e; ++i) {