IR: MDNode => Value: NamedMDNode::getOperator()

Change `NamedMDNode::getOperator()` from returning `MDNode *` to
returning `Value *`.  To reduce boilerplate at some call sites, add a
`getOperatorAsMDNode()` for named metadata that's expected to only
return `MDNode` -- for now, that's everything, but debug node named
metadata (such as llvm.dbg.cu and llvm.dbg.sp) will soon change.  This
is part of PR21433.

Note that there's a follow-up patch to clang for the API change.

llvm-svn: 221375
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index e8bff7c..ba42742 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1398,7 +1398,7 @@
 
   if (const NamedMDNode *NMD = M.getNamedMetadata("llvm.ident")) {
     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {
-      const MDNode *N = NMD->getOperand(i);
+      const MDNode *N = NMD->getOperandAsMDNode(i);
       assert(N->getNumOperands() == 1 &&
              "llvm.ident metadata entry can have only one operand");
       const MDString *S = cast<MDString>(N->getOperand(0));
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 4acd727..9523446 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -450,8 +450,8 @@
 
   SingleCU = CU_Nodes->getNumOperands() == 1;
 
-  for (MDNode *N : CU_Nodes->operands()) {
-    DICompileUnit CUNode(N);
+  for (Value *N : CU_Nodes->operands()) {
+    DICompileUnit CUNode(cast<MDNode>(N));
     DwarfCompileUnit &CU = constructDwarfCompileUnit(CUNode);
     DIArray ImportedEntities = CUNode.getImportedEntities();
     for (unsigned i = 0, e = ImportedEntities.getNumElements(); i != e; ++i)
@@ -526,8 +526,8 @@
   const Module *M = MMI->getModule();
 
   if (NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu")) {
-    for (MDNode *N : CU_Nodes->operands()) {
-      DICompileUnit TheCU(N);
+    for (Value *N : CU_Nodes->operands()) {
+      DICompileUnit TheCU(cast<MDNode>(N));
       // Construct subprogram DIE and add variables DIEs.
       DwarfCompileUnit *SPCU =
           static_cast<DwarfCompileUnit *>(CUMap.lookup(TheCU));