rustc: Fix some ThinLTO internalization

First the `addPreservedGUID` function forgot to take care of "alias" summaries.
I'm not 100% sure what this is but the current code now matches upstream. Next
the `computeDeadSymbols` return value wasn't actually being used, but it needed
to be used! Together these should...

Closes #45195

1 files changed, 8 insertions, 5 deletions

diff --git a/src/rustllvm/PassWrapper.cpp b/src/rustllvm/PassWrapper.cpp
index e37f048dd47..1287b94159a 100644
--- a/src/rustllvm/PassWrapper.cpp
+++ b/src/rustllvm/PassWrapper.cpp
@@ -901,9 +901,7 @@ addPreservedGUID(const ModuleSummaryIndex &Index,
       }
     }
 
-    GlobalValueSummary *GVSummary = Summary.get();
-    if (isa<FunctionSummary>(GVSummary)) {
-      FunctionSummary *FS = cast<FunctionSummary>(GVSummary);
+    if (auto *FS = dyn_cast<FunctionSummary>(Summary.get())) {
       for (auto &Call: FS->calls()) {
         if (Call.first.isGUID()) {
           addPreservedGUID(Index, Preserved, Call.first.getGUID());
@@ -916,6 +914,10 @@ addPreservedGUID(const ModuleSummaryIndex &Index,
         addPreservedGUID(Index, Preserved, GUID);
       }
     }
+    if (auto *AS = dyn_cast<AliasSummary>(Summary.get())) {
+      auto GUID = AS->getAliasee().getOriginalName();
+      addPreservedGUID(Index, Preserved, GUID);
+    }
   }
 }
 
@@ -963,12 +965,13 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
   // combined index
   //
   // This is copied from `lib/LTO/ThinLTOCodeGenerator.cpp`
-  computeDeadSymbols(Ret->Index, Ret->GUIDPreservedSymbols);
+  auto DeadSymbols = computeDeadSymbols(Ret->Index, Ret->GUIDPreservedSymbols);
   ComputeCrossModuleImport(
     Ret->Index,
     Ret->ModuleToDefinedGVSummaries,
     Ret->ImportLists,
-    Ret->ExportLists
+    Ret->ExportLists,
+    &DeadSymbols
   );
 
   // Resolve LinkOnce/Weak symbols, this has to be computed early be cause it