ModuleLinker: only import what is in the GlobalsToImport for ThinLTO, regarless if it is a function or not.

[mehdi_amini]

Summary

There is no change in the validation, I'm not sure if it is dead code?

[tejohnson]

The alias handling was specific to the old iterative inlining mechanism, so that is dead now. I would expect the variable handling to make a difference, since we were previously falling through to the normal selection logic. E.g. dest copy is an external decl but src has a definition - we would have picked the src copy but now will not (assuming variable not in GlobalsToImport set). I think the change is good given that is how the GlobalsToImport set is currently intended though. But would be good to confirm with a test case that previously we were doing the wrong thing w.r.t. variables and now are doing the right thing here.

lib/Linker/LinkModules.cpp

271–272

Move this up above the isDeclarationForLinker calls since the results are no longer used here.

[mehdi_amini]

Move check above

[mehdi_amini]

r266893

lib/Linker/LinkModules.cpp

bool ModuleLinker::shouldLinkFromSource(bool &LinkFromSrc,
   // We always have to add Src if it has appending linkage.
   if (Src.hasAppendingLinkage()) {
     // Should have prevented importing for appending linkage in linkIfNeeded.
     assert(!isPerformingImport());
     LinkFromSrc = true;
     return false;
   }
 
-  bool SrcIsDeclaration = Src.isDeclarationForLinker();
-  bool DestIsDeclaration = Dest.isDeclarationForLinker();
-
   if (isPerformingImport()) {
-    if (isa<Function>(&Src)) {
-      // For functions, LinkFromSrc iff this is a function requested
-      // for importing. For variables, decide below normally.
-      LinkFromSrc = GlobalsToImport->count(&Src);
-      return false;
-    }
+    // LinkFromSrc iff this is a global requested for importing.
 
-    // Check if this is an alias with an already existing definition
-    // in Dest, which must have come from a prior importing pass from
-    // the same Src module. Unlike imported function and variable
-    // definitions, which are imported as available_externally and are
-    // not definitions for the linker, that is not a valid linkage for
-    // imported aliases which must be definitions. Simply use the existing
-    // Dest copy.
-    if (isa<GlobalAlias>(&Src) && !DestIsDeclaration) {
-      assert(isa<GlobalAlias>(&Dest));
-      LinkFromSrc = false;
-      return false;
-    }
-  }
+  bool SrcIsDeclaration = Src.isDeclarationForLinker();
+  bool DestIsDeclaration = Dest.isDeclarationForLinker();
 
   if (SrcIsDeclaration) {
     // If Src is external or if both Src & Dest are external..  Just link the
     // external globals, we aren't adding anything.
     if (Src.hasDLLImportStorageClass()) {
       // If one of GVs is marked as DLLImport, result should be dllimport'ed.
       LinkFromSrc = DestIsDeclaration;
       return false;