[NFC][Cloning] Remove now unused FindDebugInfoToIdentityMap (#129151)

Summary:
This function is no longer needed.

Test Plan:
ninja check-llvm-unit

Author: artempyanykh

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

@@ -244,25 +244,6 @@ DISubprogram *CollectDebugInfoForCloning(const Function &F,
                                          CloneFunctionChangeType Changes,
                                          DebugInfoFinder &DIFinder);
 
-/// Based on \p Changes and \p DIFinder return debug info that needs to be
-/// identity mapped during Metadata cloning.
-///
-/// NOTE: Such \a MetadataSetTy can be used by \a CloneFunction* to directly
-/// specify metadata that should be identity mapped (and hence not cloned). The
-/// metadata will be identity mapped in \a ValueToValueMapTy on first use. There
-/// are several reasons for doing it this way rather than eagerly identity
-/// mapping metadata nodes in a \a ValueMap:
-/// 1. Mapping metadata is not cheap, particularly because of tracking.
-/// 2. When cloning a Function we identity map lots of global module-level
-///    metadata to avoid cloning it, while only a fraction of it is actually
-///    used by the function. Mapping on first use is a lot faster for modules
-///    with meaningful amount of debug info.
-/// 3. Eagerly identity mapping metadata makes it harder to cache module-level
-///    data (e.g. a set of metadata nodes in a \a DICompileUnit).
-MetadataSetTy FindDebugInfoToIdentityMap(CloneFunctionChangeType Changes,
-                                         DebugInfoFinder &DIFinder,
-                                         DISubprogram *SPClonedWithinModule);
-
 /// This class captures the data input to the InlineFunction call, and records
 /// the auxiliary results produced by it.
 class InlineFunctionInfo {

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -189,40 +189,6 @@ DISubprogram *llvm::CollectDebugInfoForCloning(const Function &F,
   return SPClonedWithinModule;
 }
 
-MetadataSetTy
-llvm::FindDebugInfoToIdentityMap(CloneFunctionChangeType Changes,
-                                 DebugInfoFinder &DIFinder,
-                                 DISubprogram *SPClonedWithinModule) {
-  if (Changes >= CloneFunctionChangeType::DifferentModule)
-    return {};
-
-  if (DIFinder.subprogram_count() == 0)
-    assert(!SPClonedWithinModule &&
-           "Subprogram should be in DIFinder->subprogram_count()...");
-
-  MetadataSetTy MD;
-
-  // Avoid cloning types, compile units, and (other) subprograms.
-  for (DISubprogram *ISP : DIFinder.subprograms())
-    if (ISP != SPClonedWithinModule)
-      MD.insert(ISP);
-
-  // If a subprogram isn't going to be cloned skip its lexical blocks as well.
-  for (DIScope *S : DIFinder.scopes()) {
-    auto *LScope = dyn_cast<DILocalScope>(S);
-    if (LScope && LScope->getSubprogram() != SPClonedWithinModule)
-      MD.insert(S);
-  }
-
-    for (DICompileUnit *CU : DIFinder.compile_units())
-      MD.insert(CU);
-
-    for (DIType *Type : DIFinder.types())
-      MD.insert(Type);
-
-  return MD;
-}
-
 void llvm::CloneFunctionMetadataInto(Function &NewFunc, const Function &OldFunc,
                                      ValueToValueMapTy &VMap,
                                      RemapFlags RemapFlag,