Linker: Avoid constructing ValueMap::MDMapT

Calling ValueMap::MD lazily constructs a ValueMap, which mallocs the
buckets.  Instead of swapping constructed maps, move around the
underlying Optional<MDMapT>.  This gets rid of some unnecessary malloc
traffic from r266579 (not that it showed up on a profile).

llvm-svn: 266761

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/include/llvm/IR/ValueMap.h b/llvm/include/llvm/IR/ValueMap.h
index 043e813b09b..85379ad468c 100644
--- a/llvm/include/llvm/IR/ValueMap.h
+++ b/llvm/include/llvm/IR/ValueMap.h
@@ -109,6 +109,7 @@ public:
       MDMap.emplace();
     return *MDMap;
   }
+  Optional<MDMapT> &getMDMap() { return MDMap; }
 
   bool mayMapMetadata() const { return MayMapMetadata; }
   void enableMapMetadata() { MayMapMetadata = true; }