[GlobalDCE] AvailableExternal linkage is checked in isDiscardableIfUnused [NFC].

[trentxintong]

Summary

AvailableExternal was not handled in isDiscardableIfUnused when isDiscardableIfUnused
was added in r158476. Till it was handled in r247044. This is a NFC.

[tejohnson]

I think this is an NFC (no functional change) cleanup, right? It would be good to add that in the description - i.e. put "[NFC]" at the end of the summary first line.

[trentxintong]

Address @tejohnson comment by adding NFCs to commit msg and summary.

[tejohnson]

LGTM

llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp

if (Comdat *C = GA.getComdat())
       ComdatMembers.insert(std::make_pair(C, &GA));
 
   // Loop over the module, adding globals which are obviously necessary.
   for (GlobalObject &GO : M.global_objects()) {
     Changed |= RemoveUnusedGlobalValue(GO);
     // Functions with external linkage are needed if they have a body.
     // Externally visible & appending globals are needed, if they have an
     // initializer.
-    if (!GO.isDeclaration() && !GO.hasAvailableExternallyLinkage())
+    if (!GO.isDeclaration())
       if (!GO.isDiscardableIfUnused())
         MarkLive(GO);
 
     UpdateGVDependencies(GO);
   }
 
   // Compute direct dependencies of aliases.
   for (GlobalAlias &GA : M.aliases()) {