[NFC][Utils] Extract CloneFunctionMetadataInto from CloneFunctionInto

Summary:
One potentially contentious point in the new function's API is that it expects the caller ot
populate the VMap rather than doing metadata cloning wholesale inside it.

We'll need it this way for a subsequent change.

Test Plan:
ninja check-llvm-unit

Author: artempyanykh

llvm/include/llvm/Transforms/Utils/Cloning.h

@@ -180,6 +180,18 @@ void CloneFunctionAttributesInto(Function *NewFunc, const Function *OldFunc,
                                  ValueMapTypeRemapper *TypeMapper = nullptr,
                                  ValueMaterializer *Materializer = nullptr);
 
+/// Clone OldFunc's metadata into NewFunc.
+///
+/// The caller is expected to populate \p VMap beforehand and set an appropriate
+/// \p RemapFlag.
+///
+/// NOTE: This function doesn't clone !llvm.dbg.cu when cloning into a different
+/// module. Use CloneFunctionInto for that behavior.
+void CloneFunctionMetadataInto(Function *NewFunc, const Function *OldFunc,
+                               ValueToValueMapTy &VMap, RemapFlags RemapFlag,
+                               ValueMapTypeRemapper *TypeMapper = nullptr,
+                               ValueMaterializer *Materializer = nullptr);
+
 void CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
                                const Instruction *StartingInst,
                                ValueToValueMapTy &VMap, bool ModuleLevelChanges,

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -200,6 +200,22 @@ bool llvm::BuildDebugInfoMDMap(MDMapT &MD, CloneFunctionChangeType Changes,
   return ModuleLevelChanges;
 }
 
+void llvm::CloneFunctionMetadataInto(Function *NewFunc, const Function *OldFunc,
+                                     ValueToValueMapTy &VMap,
+                                     RemapFlags RemapFlag,
+                                     ValueMapTypeRemapper *TypeMapper,
+                                     ValueMaterializer *Materializer) {
+  // Duplicate the metadata that is attached to the cloned function.
+  // Subprograms/CUs/types that were already mapped to themselves won't be
+  // duplicated.
+  SmallVector<std::pair<unsigned, MDNode *>, 1> MDs;
+  OldFunc->getAllMetadata(MDs);
+  for (auto MD : MDs) {
+    NewFunc->addMetadata(MD.first, *MapMetadata(MD.second, VMap, RemapFlag,
+                                                TypeMapper, Materializer));
+  }
+}
+
 // Clone OldFunc into NewFunc, transforming the old arguments into references to
 // VMap values.
 void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
@@ -263,15 +279,9 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
       BuildDebugInfoMDMap(VMap.MD(), Changes, DIFinder, SPClonedWithinModule);
 
   const auto RemapFlag = ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges;
-  // Duplicate the metadata that is attached to the cloned function.
-  // Subprograms/CUs/types that were already mapped to themselves won't be
-  // duplicated.
-  SmallVector<std::pair<unsigned, MDNode *>, 1> MDs;
-  OldFunc->getAllMetadata(MDs);
-  for (auto MD : MDs) {
-    NewFunc->addMetadata(MD.first, *MapMetadata(MD.second, VMap, RemapFlag,
-                                                TypeMapper, Materializer));
-  }
+
+  CloneFunctionMetadataInto(NewFunc, OldFunc, VMap, RemapFlag, TypeMapper,
+                            Materializer);
 
   // Loop over all of the basic blocks in the function, cloning them as
   // appropriate.  Note that we save BE this way in order to handle cloning of