IR: Store RAUW support and Context in the same pointer, NFC

Add an `LLVMContext &` to `ReplaceableMetadataImpl`, create a class that
either holds a reference to an `LLVMContext` or owns a
`ReplaceableMetadataImpl`, and use the new class in `MDNode`.

  - This saves a pointer in `UniquableMDNode` at the cost of a pointer
    in `ValueAsMetadata` (which didn't used to store the `LLVMContext`).
    There are far more of the former.
  - Unifies RAUW support between `MDNodeFwdDecl` (which is going away,
    see r226481) and `UniquableMDNode`.

llvm-svn: 226484

1 files changed, 2 insertions, 5 deletions

diff --git a/llvm/lib/IR/MetadataTracking.cpp b/llvm/lib/IR/MetadataTracking.cpp
index ba97ca033a4..47f0b9366d7 100644
--- a/llvm/lib/IR/MetadataTracking.cpp
+++ b/llvm/lib/IR/MetadataTracking.cpp
@@ -17,11 +17,8 @@
 using namespace llvm;
 
 ReplaceableMetadataImpl *ReplaceableMetadataImpl::get(Metadata &MD) {
-  if (auto *N = dyn_cast<MDNode>(&MD)) {
-    if (auto *U = dyn_cast<UniquableMDNode>(N))
-      return U->ReplaceableUses.get();
-    return cast<MDNodeFwdDecl>(N);
-  }
+  if (auto *N = dyn_cast<MDNode>(&MD))
+    return N->Context.getReplaceableUses();
   return dyn_cast<ValueAsMetadata>(&MD);
 }