[ThinLTO] Move global processing from Linker to TransformUtils (NFC)

Summary:
As discussed on IRC, move the ThinLTOGlobalProcessing code out of
the linker, and into TransformUtils. The name of the class is changed
to FunctionImportGlobalProcessing.

Reviewers: joker.eph, rafael

Subscribers: joker.eph, llvm-commits

Differential Revision: http://reviews.llvm.org/D17081

llvm-svn: 260395

llvm/include/llvm/Linker/Linker.h

@@ -67,10 +67,6 @@ class Linker {
                       DenseMap<unsigned, MDNode *> *ValIDToTempMDMap);
 };
 
-/// Perform in-place global value handling on the given Module for
-/// exported local functions renamed and promoted for ThinLTO.
-bool renameModuleForThinLTO(Module &M, const FunctionInfoIndex *Index);
-
 } // End llvm namespace
 
 #endif

llvm/include/llvm/Transforms/Utils/FunctionImportUtils.h

@@ -0,0 +1,106 @@
+//===- FunctionImportUtils.h - Importing support utilities -----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the FunctionImportGlobalProcessing class which is used
+// to perform the necessary global value handling for function importing.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_FUNCTIONIMPORTUTILS_H
+#define LLVM_TRANSFORMS_UTILS_FUNCTIONIMPORTUTILS_H
+
+#include "llvm/ADT/SetVector.h"
+#include "llvm/IR/FunctionInfo.h"
+
+namespace llvm {
+class Module;
+
+/// Class to handle necessary GlobalValue changes required by ThinLTO
+/// function importing, including linkage changes and any necessary renaming.
+class FunctionImportGlobalProcessing {
+  /// The Module which we are exporting or importing functions from.
+  Module &M;
+
+  /// Function index passed in for function importing/exporting handling.
+  const FunctionInfoIndex *ImportIndex;
+
+  /// Functions to import from this module, all other functions will be
+  /// imported as declarations instead of definitions.
+  DenseSet<const GlobalValue *> *FunctionsToImport;
+
+  /// Set to true if the given FunctionInfoIndex contains any functions
+  /// from this source module, in which case we must conservatively assume
+  /// that any of its functions may be imported into another module
+  /// as part of a different backend compilation process.
+  bool HasExportedFunctions = false;
+
+  /// Populated during ThinLTO global processing with locals promoted
+  /// to global scope in an exporting module, which now need to be linked
+  /// in if calling from the ModuleLinker.
+  SetVector<GlobalValue *> NewExportedValues;
+
+  /// Check if we should promote the given local value to global scope.
+  bool doPromoteLocalToGlobal(const GlobalValue *SGV);
+
+  /// Helper methods to check if we are importing from or potentially
+  /// exporting from the current source module.
+  bool isPerformingImport() const { return FunctionsToImport != nullptr; }
+  bool isModuleExporting() const { return HasExportedFunctions; }
+
+  /// If we are importing from the source module, checks if we should
+  /// import SGV as a definition, otherwise import as a declaration.
+  bool doImportAsDefinition(const GlobalValue *SGV);
+
+  /// Get the name for SGV that should be used in the linked destination
+  /// module. Specifically, this handles the case where we need to rename
+  /// a local that is being promoted to global scope.
+  std::string getName(const GlobalValue *SGV);
+
+  /// Process globals so that they can be used in ThinLTO. This includes
+  /// promoting local variables so that they can be reference externally by
+  /// thin lto imported globals and converting strong external globals to
+  /// available_externally.
+  void processGlobalsForThinLTO();
+  void processGlobalForThinLTO(GlobalValue &GV);
+
+  /// Get the new linkage for SGV that should be used in the linked destination
+  /// module. Specifically, for ThinLTO importing or exporting it may need
+  /// to be adjusted.
+  GlobalValue::LinkageTypes getLinkage(const GlobalValue *SGV);
+
+public:
+  FunctionImportGlobalProcessing(
+      Module &M, const FunctionInfoIndex *Index,
+      DenseSet<const GlobalValue *> *FunctionsToImport = nullptr)
+      : M(M), ImportIndex(Index), FunctionsToImport(FunctionsToImport) {
+    // If we have a FunctionInfoIndex but no function to import,
+    // then this is the primary module being compiled in a ThinLTO
+    // backend compilation, and we need to see if it has functions that
+    // may be exported to another backend compilation.
+    if (!FunctionsToImport)
+      HasExportedFunctions = ImportIndex->hasExportedFunctions(M);
+  }
+
+  bool run();
+
+  static bool
+  doImportAsDefinition(const GlobalValue *SGV,
+                       DenseSet<const GlobalValue *> *FunctionsToImport);
+
+  /// Access the promoted globals that are now exported and need to be linked.
+  SetVector<GlobalValue *> &getNewExportedValues() { return NewExportedValues; }
+};
+
+/// Perform in-place global value handling on the given Module for
+/// exported local functions renamed and promoted for ThinLTO.
+bool renameModuleForThinLTO(Module &M, const FunctionInfoIndex *Index);
+
+} // End llvm namespace
+
+#endif