Add allnodes() iterator range to SelectionDAG.  NFC.

SelectionDAG already had begin/end methods for iterating over all
the nodes, but didn't define an iterator_range for us in foreach
loops.

This adds such a method and uses it in some of the eligible places
throughout the backends.

llvm-svn: 242212
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 41bb57a..01a3acb 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -3406,9 +3406,8 @@
   bool IsModified;
   do {
     IsModified = false;
-    for (SelectionDAG::allnodes_iterator I = CurDAG->allnodes_begin(),
-         E = CurDAG->allnodes_end(); I != E; ++I) {
-      MachineSDNode *MachineNode = dyn_cast<MachineSDNode>(I);
+    for (SDNode &Node : CurDAG->allnodes()) {
+      MachineSDNode *MachineNode = dyn_cast<MachineSDNode>(&Node);
       if (!MachineNode || MachineNode->use_empty())
         continue;
       SDNode *ResNode = MachineNode;