[ThinLTO] Use original alias visibility when importing

[tejohnson]

Summary

When we import an alias, we do so by making a clone of the aliasee. Just
as this clone uses the original alias name and linkage, it should also
use the same visibility (not the aliasee's visibility). Otherwise,
linker behavior is affected (e.g. if the aliasee was hidden, but the
alias is not, the resulting imported clone should not be hidden,
otherwise the linker will make the final symbol hidden which is
incorrect).

[wmi]

LGTM.

lib/Transforms/IPO/FunctionImport.cpp

 }
 
 /// Make alias a clone of its aliasee.
 static Function *replaceAliasWithAliasee(Module *SrcModule, GlobalAlias *GA) {
   Function *Fn = cast<Function>(GA->getBaseObject());
 
   ValueToValueMapTy VMap;
   Function *NewFn = CloneFunction(Fn, VMap);
-  // Clone should use the original alias's linkage and name, and we ensure
-  // all uses of alias instead use the new clone (casted if necessary).
+  // Clone should use the original alias's linkage, visibility and name, and we
+  // ensure all uses of alias instead use the new clone (casted if necessary).
   NewFn->setLinkage(GA->getLinkage());
+  NewFn->setVisibility(GA->getVisibility());
   GA->replaceAllUsesWith(ConstantExpr::getBitCast(NewFn, GA->getType()));
   NewFn->takeName(GA);
   return NewFn;
 }
 
 // Internalize values that we marked with specific attribute
 // in processGlobalForThinLTO.
 static void internalizeImmutableGVs(Module &M) {

test/ThinLTO/X86/Inputs/alias_import.ll

 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 
 @globalfuncAlias = alias void (...), bitcast (void ()* @globalfunc to void (...)*)
 @globalfuncWeakAlias = weak alias void (...), bitcast (void ()* @globalfunc to void (...)*)
 @globalfuncLinkonceAlias = linkonce alias void (...), bitcast (void ()* @globalfunc to void (...)*)
 @globalfuncWeakODRAlias = weak_odr alias void (...), bitcast (void ()* @globalfunc to void (...)*)
 @globalfuncLinkonceODRAlias = linkonce_odr alias void (...), bitcast (void ()* @globalfunc to void (...)*)
-define void @globalfunc() {
+define hidden void @globalfunc() {
 entry:
   ret void
 }
 
 @internalfuncAlias = alias void (...), bitcast (void ()* @internalfunc to void (...)*)
 @internalfuncWeakAlias = weak alias void (...), bitcast (void ()* @internalfunc to void (...)*)
 @internalfuncLinkonceAlias = linkonce alias void (...), bitcast (void ()* @internalfunc to void (...)*)
 @internalfuncWeakODRAlias = weak_odr alias void (...), bitcast (void ()* @internalfunc to void (...)*)

test/ThinLTO/X86/alias_import.ll

 ; PROMOTE-DAG: @weakODRfuncWeakODRAlias = weak_odr alias void (...), bitcast (void ()* @weakODRfunc to void (...)*)
 ; PROMOTE-DAG: @weakODRfuncLinkonceODRAlias = weak_odr alias void (...), bitcast (void ()* @weakODRfunc to void (...)*)
 ; PROMOTE-DAG: @linkonceODRfuncAlias = alias void (...), bitcast (void ()* @linkonceODRfunc to void (...)*)
 ; PROMOTE-DAG: @linkonceODRfuncWeakAlias = weak alias void (...), bitcast (void ()* @linkonceODRfunc to void (...)*)
 ; PROMOTE-DAG: @linkonceODRfuncWeakODRAlias = weak_odr alias void (...), bitcast (void ()* @linkonceODRfunc to void (...)*)
 ; PROMOTE-DAG: @linkonceODRfuncLinkonceAlias = weak alias void (...), bitcast (void ()* @linkonceODRfunc to void (...)*)
 ; PROMOTE-DAG: @linkonceODRfuncLinkonceODRAlias = weak_odr alias void (...), bitcast (void ()* @linkonceODRfunc to void (...)*)
 
-; PROMOTE-DAG: define void @globalfunc()
+; PROMOTE-DAG: define hidden void @globalfunc()
 ; PROMOTE-DAG: define internal void @internalfunc()
 ; PROMOTE-DAG: define weak_odr void @linkonceODRfunc()
 ; PROMOTE-DAG: define weak_odr void @weakODRfunc()
 ; PROMOTE-DAG: define weak void @linkoncefunc()
 ; PROMOTE-DAG: define weak void @weakfunc()
 
 ; On the import side now, verify that aliases are imported unless they
 ; are preemptible (non-ODR weak/linkonce).
 ; IMPORT-DAG: declare void @linkonceODRfuncWeakAlias
 ; IMPORT-DAG: declare void @linkonceODRfuncLinkonceAlias
 ; IMPORT-DAG: define available_externally void @linkonceODRfuncAlias
 ; IMPORT-DAG: define available_externally void @linkonceODRfuncWeakODRAlias
 ; IMPORT-DAG: define available_externally void @linkonceODRfuncLinkonceODRAlias
-; IMPORT-DAG: define available_externally void @globalfuncAlias()
+; IMPORT-DAG: define available_externally dso_local void @globalfuncAlias()
 ; IMPORT-DAG: declare void @globalfuncWeakAlias()
 ; IMPORT-DAG: declare void @globalfuncLinkonceAlias()
-; IMPORT-DAG: define available_externally void @globalfuncWeakODRAlias()
-; IMPORT-DAG: define available_externally void @globalfuncLinkonceODRAlias()
+; IMPORT-DAG: define available_externally dso_local void @globalfuncWeakODRAlias()
+; IMPORT-DAG: define available_externally dso_local void @globalfuncLinkonceODRAlias()
 ; IMPORT-DAG: define available_externally dso_local void @internalfuncAlias()
 ; IMPORT-DAG: declare void @internalfuncWeakAlias()
 ; IMPORT-DAG: declare void @internalfuncLinkonceAlias()
 ; IMPORT-DAG: define available_externally dso_local void @internalfuncWeakODRAlias()
 ; IMPORT-DAG: define available_externally dso_local void @internalfuncLinkonceODRAlias()
 ; IMPORT-DAG: define available_externally void @weakODRfuncAlias()
 ; IMPORT-DAG: declare void @weakODRfuncWeakAlias()
 ; IMPORT-DAG: declare void @weakODRfuncLinkonceAlias()