[CloneFunction][DebugInfo] Ensure DILocalVariables of inlined functions are not cloned (NFC) (#138590)

This change was separated from
#119001.

When cloning functions, use IdentityMDPredicate to ensure that if
DISubprogram is not cloned, then its DILocalVariables are not cloned
either.

This is currently expected to be an NFC, as DILocalVariables only
reference their subprograms (via DILocalScopes) and types, and inlined
DISubprograms and DITypes are not cloned. Thus, DILocalVariables are
mapped to self in ValueMapper (in mapTopLevelUniquedNode).

However, it will be needed for the original PR
#119001, where a
DILocalVariable may refer to a local type of a DISubprogram that is
being cloned. In that case, ValueMapper will clone DILocalVariable even
if it belongs to an inlined DISubprogram that is not cloned, which
should be avoided.
I'm making this change into a separate PR to make the original PR a bit
smaller, and because this has more to do with variables than with types.

Author: dzhidzhoev

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -81,17 +81,28 @@ MetadataPredicate createIdentityMDPredicate(const Function &F,
     return [](const Metadata *MD) { return false; };
 
   DISubprogram *SPClonedWithinModule = F.getSubprogram();
+
+  // Don't clone inlined subprograms.
+  auto ShouldKeep = [SPClonedWithinModule](const DISubprogram *SP) -> bool {
+    return SP != SPClonedWithinModule;
+  };
+
   return [=](const Metadata *MD) {
     // Avoid cloning types, compile units, and (other) subprograms.
     if (isa<DICompileUnit>(MD) || isa<DIType>(MD))
       return true;
 
     if (auto *SP = dyn_cast<DISubprogram>(MD))
-      return SP != SPClonedWithinModule;
+      return ShouldKeep(SP);
 
     // If a subprogram isn't going to be cloned skip its lexical blocks as well.
     if (auto *LScope = dyn_cast<DILocalScope>(MD))
-      return LScope->getSubprogram() != SPClonedWithinModule;
+      return ShouldKeep(LScope->getSubprogram());
+
+    // Avoid cloning local variables of subprograms that won't be cloned.
+    if (auto *DV = dyn_cast<DILocalVariable>(MD))
+      if (auto *S = dyn_cast_or_null<DILocalScope>(DV->getScope()))
+        return ShouldKeep(S->getSubprogram());
 
     return false;
   };