[LTO] Introduce new type alias ImportListsTy (NFC) (#106420)

The background is as follows.  I'm planning to reduce the memory
footprint of ThinLTO indexing by changing ImportMapTy, the data
structure used for an import list.  Once this patch lands, I'm
planning to change the type slightly.  The new type alias allows us to
update the type without touching many places.

llvm/include/llvm/Transforms/IPO/FunctionImport.h

@@ -149,6 +149,9 @@ class FunctionImporter {
     ImportMapTyImpl ImportMap;
   };
 
+  // A map from destination modules to lists of imports.
+  using ImportListsTy = DenseMap<StringRef, ImportMapTy>;
+
   /// The set contains an entry for every global value that the module exports.
   /// Depending on the user context, this container is allowed to contain
   /// definitions, declarations or a mix of both.
@@ -211,7 +214,7 @@ void ComputeCrossModuleImport(
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing,
-    DenseMap<StringRef, FunctionImporter::ImportMapTy> &ImportLists,
+    FunctionImporter::ImportListsTy &ImportLists,
     DenseMap<StringRef, FunctionImporter::ExportSetTy> &ExportLists);
 
 /// PrevailingType enum used as a return type of callback passed

llvm/lib/LTO/LTO.cpp

@@ -1716,8 +1716,7 @@ Error LTO::runThinLTO(AddStreamFn AddStream, FileCache Cache,
   // Synthesize entry counts for functions in the CombinedIndex.
   computeSyntheticCounts(ThinLTO.CombinedIndex);
 
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists(
-      ThinLTO.ModuleMap.size());
+  FunctionImporter::ImportListsTy ImportLists(ThinLTO.ModuleMap.size());
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists(
       ThinLTO.ModuleMap.size());
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;

llvm/lib/LTO/ThinLTOCodeGenerator.cpp

@@ -693,7 +693,7 @@ void ThinLTOCodeGenerator::promote(Module &TheModule, ModuleSummaryIndex &Index,
   computePrevailingCopies(Index, PrevailingCopy);
 
   // Generate import/export list
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
+  FunctionImporter::ImportListsTy ImportLists(ModuleCount);
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries,
                            IsPrevailing(PrevailingCopy), ImportLists,
@@ -745,7 +745,7 @@ void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
   computePrevailingCopies(Index, PrevailingCopy);
 
   // Generate import/export list
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
+  FunctionImporter::ImportListsTy ImportLists(ModuleCount);
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries,
                            IsPrevailing(PrevailingCopy), ImportLists,
@@ -785,7 +785,7 @@ void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
   computePrevailingCopies(Index, PrevailingCopy);
 
   // Generate import/export list
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
+  FunctionImporter::ImportListsTy ImportLists(ModuleCount);
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries,
                            IsPrevailing(PrevailingCopy), ImportLists,
@@ -823,7 +823,7 @@ void ThinLTOCodeGenerator::emitImports(Module &TheModule, StringRef OutputName,
   computePrevailingCopies(Index, PrevailingCopy);
 
   // Generate import/export list
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
+  FunctionImporter::ImportListsTy ImportLists(ModuleCount);
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries,
                            IsPrevailing(PrevailingCopy), ImportLists,
@@ -874,7 +874,7 @@ void ThinLTOCodeGenerator::internalize(Module &TheModule,
   computePrevailingCopies(Index, PrevailingCopy);
 
   // Generate import/export list
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
+  FunctionImporter::ImportListsTy ImportLists(ModuleCount);
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries,
                            IsPrevailing(PrevailingCopy), ImportLists,
@@ -1074,7 +1074,7 @@ void ThinLTOCodeGenerator::run() {
 
   // Collect the import/export lists for all modules from the call-graph in the
   // combined index.
-  DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
+  FunctionImporter::ImportListsTy ImportLists(ModuleCount);
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(*Index, ModuleToDefinedGVSummaries,
                            IsPrevailing(PrevailingCopy), ImportLists,

llvm/lib/Transforms/IPO/FunctionImport.cpp

@@ -1111,7 +1111,7 @@ collectImportStatistics(const ModuleSummaryIndex &Index,
 #ifndef NDEBUG
 static bool checkVariableImport(
     const ModuleSummaryIndex &Index,
-    DenseMap<StringRef, FunctionImporter::ImportMapTy> &ImportLists,
+    FunctionImporter::ImportListsTy &ImportLists,
     DenseMap<StringRef, FunctionImporter::ExportSetTy> &ExportLists) {
   DenseSet<GlobalValue::GUID> FlattenedImports;
 
@@ -1152,7 +1152,7 @@ void llvm::ComputeCrossModuleImport(
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing,
-    DenseMap<StringRef, FunctionImporter::ImportMapTy> &ImportLists,
+    FunctionImporter::ImportListsTy &ImportLists,
     DenseMap<StringRef, FunctionImporter::ExportSetTy> &ExportLists) {
   auto MIS = ModuleImportsManager::create(isPrevailing, Index, &ExportLists);
   // For each module that has function defined, compute the import/export lists.