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/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 33620e7..adaa12e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6385,7 +6385,7 @@
     const SDNode *M = Worklist.pop_back_val();
     for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i) {
       SDNode *Op = M->getOperand(i).getNode();
-      if (Visited.insert(Op))
+      if (Visited.insert(Op).second)
         Worklist.push_back(Op);
       if (Op == N)
         return true;
@@ -6753,7 +6753,7 @@
 
   // If a node has already been visited on this depth-first walk, reject it as
   // a cycle.
-  if (!Visited.insert(N)) {
+  if (!Visited.insert(N).second) {
     errs() << "Detected cycle in SelectionDAG\n";
     dbgs() << "Offending node:\n";
     N->dumprFull(DAG); dbgs() << "\n";