[ThinLTO] Clean up stale alias import handling

[tejohnson]

Summary

Remove some code that was no longer needed. The first FIXME is
stale since we long ago started using the index to drive importing,
rather than doing force importing based on linkage type. And
now with r309278, we no longer import any aliases.

[dblaikie]

Is it worth having the DEBUG output if no aliases are ever imported?

Could potentially rewrite this whole loop as:

assert(none_of(SrcModule.aliases(), [&](GlobalAlias &GA) { if (!GA.hasName()) return false; return ImportGUIDs.count(GA.getGUID()); }) && "Unexpected alias in import list");

Dunno if that comes out more legible, though.

[tejohnson]

In D37266#855617, @dblaikie wrote:

Is it worth having the DEBUG output if no aliases are ever imported?

I think it is worthwhile emitting this since we also emit the functions/vars that are not imported.

Could potentially rewrite this whole loop as:

assert(none_of(SrcModule.aliases(), [&](GlobalAlias &GA) { if (!GA.hasName()) return false; return ImportGUIDs.count(GA.getGUID()); }) && "Unexpected alias in import list");

Dunno if that comes out more legible, though.

I was trying to keep it somewhat symmetric with the earlier code handling functions and variables. I'm hoping to start looking at importing these as a copy, which would mean this would go back to a loop anyway. I will change it if you feel strongly that this is better though.

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

for (GlobalVariable &GV : SrcModule->globals()) {
                    << SrcModule->getSourceFileName() << "\n");
       if (Import) {
         if (Error Err = GV.materialize())
           return std::move(Err);
         GlobalsToImport.insert(&GV);
       }
     }
     for (GlobalAlias &GA : SrcModule->aliases()) {
-      // FIXME: This should eventually be controlled entirely by the summary.
-      if (FunctionImportGlobalProcessing::doImportAsDefinition(
-              &GA, &GlobalsToImport)) {
-        GlobalsToImport.insert(&GA);
-        continue;
-      }
-
       if (!GA.hasName())
         continue;
       auto GUID = GA.getGUID();
-      auto Import = ImportGUIDs.count(GUID);
-      DEBUG(dbgs() << (Import ? "Is" : "Not") << " importing alias " << GUID
+      assert(!ImportGUIDs.count(GUID) && "Unexpected alias in import list");
+      DEBUG(dbgs() << "Not importing alias " << GUID
                    << " " << GA.getName() << " from "
                    << SrcModule->getSourceFileName() << "\n");
-      if (Import) {
-        // Alias can't point to "available_externally". However when we import
-        // linkOnceODR the linkage does not change. So we import the alias
-        // and aliasee only in this case. This has been handled by
-        // computeImportForFunction()
-        GlobalObject *GO = GA.getBaseObject();
-        assert(GO->hasLinkOnceODRLinkage() &&
-               "Unexpected alias to a non-linkonceODR in import list");
-#ifndef NDEBUG
-        if (!GlobalsToImport.count(GO))
-          DEBUG(dbgs() << " alias triggers importing aliasee " << GO->getGUID()
-                       << " " << GO->getName() << " from "
-                       << SrcModule->getSourceFileName() << "\n");
-#endif
-        if (Error Err = GO->materialize())
-          return std::move(Err);
-        GlobalsToImport.insert(GO);
-        if (Error Err = GA.materialize())
-          return std::move(Err);
-        GlobalsToImport.insert(&GA);
-      }
     }
 
     // Upgrade debug info after we're done materializing all the globals and we
     // have loaded all the required metadata!
     UpgradeDebugInfo(*SrcModule);
 
     // Link in the specified functions.
     if (renameModuleForThinLTO(*SrcModule, Index, &GlobalsToImport))