IR: Remove MDNodeFwdDecl

Remove `MDNodeFwdDecl` (as promised in r226481).  Aside from API
changes, there's no real functionality change here.
`MDNode::getTemporary()` now forwards to `MDTuple::getTemporary()`,
which returns a tuple with `isTemporary()` equal to true.

The main point is that we can now add temporaries of other `MDNode`
subclasses, needed for PR22235 (I introduced `MDNodeFwdDecl` in the
first place because I didn't recognize this need, and thought they were
only needed to handle forward references).

A few things left out of (or highlighted by) this commit:

  - I've had to remove the (few) uses of `std::unique_ptr<>` to deal
    with temporaries, since the destructor is no longer public.
    `getTemporary()` should probably return the equivalent of
    `std::unique_ptr<T, MDNode::deleteTemporary>`.
  - `MDLocation::getTemporary()` doesn't exist yet (worse, it actually
    does exist, but does the wrong thing: `MDNode::getTemporary()` is
    inherited and returns an `MDTuple`).
  - `MDNode` now only has one subclass, `UniquableMDNode`, and the
    distinction between them is actually somewhat confusing.

I'll fix those up next.

llvm-svn: 226501

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/IR/DebugInfo.cpp b/llvm/lib/IR/DebugInfo.cpp
index 290dbe29c70..c5c11157971 100644
--- a/llvm/lib/IR/DebugInfo.cpp
+++ b/llvm/lib/IR/DebugInfo.cpp
@@ -337,7 +337,8 @@ void DIDescriptor::replaceAllUsesWith(LLVMContext &VMContext, DIDescriptor D) {
     DN = MDNode::get(VMContext, Ops);
   }
 
-  auto *Node = cast<MDNodeFwdDecl>(const_cast<MDNode *>(DbgNode));
+  assert(DbgNode->isTemporary() && "Expected temporary node");
+  auto *Node = const_cast<MDNode *>(DbgNode);
   Node->replaceAllUsesWith(const_cast<MDNode *>(DN));
   MDNode::deleteTemporary(Node);
   DbgNode = DN;
@@ -346,7 +347,8 @@ void DIDescriptor::replaceAllUsesWith(LLVMContext &VMContext, DIDescriptor D) {
 void DIDescriptor::replaceAllUsesWith(MDNode *D) {
   assert(DbgNode && "Trying to replace an unverified type!");
   assert(DbgNode != D && "This replacement should always happen");
-  auto *Node = cast<MDNodeFwdDecl>(const_cast<MDNode *>(DbgNode));
+  assert(DbgNode->isTemporary() && "Expected temporary node");
+  auto *Node = const_cast<MDNode *>(DbgNode);
   Node->replaceAllUsesWith(D);
   MDNode::deleteTemporary(Node);
 }