ModuleLinker: Remove importing support. NFCI.

[pcc]

Summary

Depends on D29468

[mehdi_amini]

Nice cleanup. Thanks.
LGTM.

llvm/include/llvm/Linker/Linker.h

class Linker {
   IRMover Mover;
 
 public:
   enum Flags {
     None = 0,
     OverrideFromSrc = (1 << 0),
     LinkOnlyNeeded = (1 << 1),
     InternalizeLinkedSymbols = (1 << 2),
-    /// Don't force link referenced linkonce definitions, import declaration.
-    DontForceLinkLinkonceODR = (1 << 3)
-
   };
 
   Linker(Module &M);
 
   /// \brief Link \p Src into the composite.
   ///
   /// Passing OverrideSymbols as true will have symbols from Src
   /// shadow those in the Dest.
-  /// For ThinLTO function importing/exporting the \p ModuleSummaryIndex
-  /// is passed. If \p GlobalsToImport is provided, only the globals that
-  /// are part of the set will be imported from the source module.
   ///
   /// Returns true on error.
-  bool linkInModule(std::unique_ptr<Module> Src, unsigned Flags = Flags::None,
-                    DenseSet<const GlobalValue *> *GlobalsToImport = nullptr);
+  bool linkInModule(std::unique_ptr<Module> Src, unsigned Flags = Flags::None);
 
   static bool linkModules(Module &Dest, std::unique_ptr<Module> Src,
                           unsigned Flags = Flags::None);
 };
 
 } // End llvm namespace
 
 #endif

llvm/lib/Linker/LinkModules.cpp

 // This file implements the LLVM module linker.
 //
 //===----------------------------------------------------------------------===//
 
 #include "LinkDiagnosticInfo.h"
 #include "llvm-c/Linker.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/StringSet.h"
+#include "llvm/IR/Comdat.h"
 #include "llvm/IR/DiagnosticPrinter.h"
+#include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
 #include "llvm/Linker/Linker.h"
 #include "llvm/Support/Error.h"
-#include "llvm/Transforms/Utils/FunctionImportUtils.h"
 using namespace llvm;
 
 namespace {
 
 /// This is an implementation class for the LinkModules function, which is the
 /// entrypoint for this file.
 class ModuleLinker {
   IRMover &Mover;
   std::unique_ptr<Module> SrcM;
 
   SetVector<GlobalValue *> ValuesToLink;
   StringSet<> Internalize;
 
   /// For symbol clashes, prefer those from Src.
   unsigned Flags;
 
-  /// Functions to import from source module, all other functions are
-  /// imported as declarations instead of definitions.
-  DenseSet<const GlobalValue *> *GlobalsToImport;
-
   /// Used as the callback for lazy linking.
   /// The mover has just hit GV and we have to decide if it, and other members
   /// of the same comdat, should be linked. Every member to be linked is passed
   /// to Add.
   void addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add);
 
-  bool shouldLinkReferencedLinkOnce() {
-    return !(Flags & Linker::DontForceLinkLinkonceODR);
-  }
   bool shouldOverrideFromSrc() { return Flags & Linker::OverrideFromSrc; }
   bool shouldLinkOnlyNeeded() { return Flags & Linker::LinkOnlyNeeded; }
   bool shouldInternalizeLinkedSymbols() {
     return Flags & Linker::InternalizeLinkedSymbols;
   }
 
   bool shouldLinkFromSource(bool &LinkFromSrc, const GlobalValue &Dest,
                             const GlobalValue &Src);
class ModuleLinker {
 
   /// Drop GV if it is a member of a comdat that we are dropping.
   /// This can happen with COFF's largest selection kind.
   void dropReplacedComdat(GlobalValue &GV,
                           const DenseSet<const Comdat *> &ReplacedDstComdats);
 
   bool linkIfNeeded(GlobalValue &GV);
 
-  /// Helper method to check if we are importing from the current source
-  /// module.
-  bool isPerformingImport() const { return GlobalsToImport != nullptr; }
-
-  /// 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);
-
 public:
-  ModuleLinker(IRMover &Mover, std::unique_ptr<Module> SrcM, unsigned Flags,
-               DenseSet<const GlobalValue *> *GlobalsToImport = nullptr)
-      : Mover(Mover), SrcM(std::move(SrcM)), Flags(Flags),
-        GlobalsToImport(GlobalsToImport) {}
+  ModuleLinker(IRMover &Mover, std::unique_ptr<Module> SrcM, unsigned Flags)
+      : Mover(Mover), SrcM(std::move(SrcM)), Flags(Flags) {}
 
   bool run();
 };
 }
 
-bool ModuleLinker::doImportAsDefinition(const GlobalValue *SGV) {
-  if (!isPerformingImport())
-    return false;
-  report_fatal_error("ModuleLinker does not support importing");
-}
-
 static GlobalValue::VisibilityTypes
 getMinVisibility(GlobalValue::VisibilityTypes A,
                  GlobalValue::VisibilityTypes B) {
   if (A == GlobalValue::HiddenVisibility || B == GlobalValue::HiddenVisibility)
     return GlobalValue::HiddenVisibility;
   if (A == GlobalValue::ProtectedVisibility ||
       B == GlobalValue::ProtectedVisibility)
     return GlobalValue::ProtectedVisibility;
bool ModuleLinker::shouldLinkFromSource(bool &LinkFromSrc,
   // Should we unconditionally use the Src?
   if (shouldOverrideFromSrc()) {
     LinkFromSrc = true;
     return false;
   }
 
   // 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;
   }
 
-  if (isPerformingImport()) {
-    // LinkFromSrc iff this is a global requested for importing.
-    LinkFromSrc = GlobalsToImport->count(&Src);
-    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.
if (DGV && !GV.hasLocalLinkage() && !GV.hasAppendingLinkage()) {
     GV.setVisibility(Visibility);
 
     GlobalValue::UnnamedAddr UnnamedAddr = GlobalValue::getMinUnnamedAddr(
         DGV->getUnnamedAddr(), GV.getUnnamedAddr());
     DGV->setUnnamedAddr(UnnamedAddr);
     GV.setUnnamedAddr(UnnamedAddr);
   }
 
-  // Don't want to append to global_ctors list, for example, when we
-  // are importing for ThinLTO, otherwise the global ctors and dtors
-  // get executed multiple times for local variables (the latter causing
-  // double frees).
-  if (GV.hasAppendingLinkage() && isPerformingImport())
-    return false;
-
-  if (isPerformingImport()) {
-    if (!doImportAsDefinition(&GV))
-      return false;
-  } else if (!DGV && !shouldOverrideFromSrc() &&
-             (GV.hasLocalLinkage() || GV.hasLinkOnceLinkage() ||
-              GV.hasAvailableExternallyLinkage()))
+  if (!DGV && !shouldOverrideFromSrc() &&
     return false;
 
   if (GV.isDeclaration())
     return false;
 
   if (const Comdat *SC = GV.getComdat()) {
     bool LinkFromSrc;
     Comdat::SelectionKind SK;
     std::tie(SK, LinkFromSrc) = ComdatsChosen[SC];
     if (!LinkFromSrc)
       return false;
   }
 
   bool LinkFromSrc = true;
   if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, GV))
     return true;
   if (LinkFromSrc)
     ValuesToLink.insert(&GV);
   return false;
 }
 
 void ModuleLinker::addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add) {
-  if (!shouldLinkReferencedLinkOnce())
-    // For ThinLTO we don't import more than what was required.
-    // The client has to guarantee that the linkonce will be availabe at link
-    // time (by promoting it to weak for instance).
-    return;
-
   // Add these to the internalize list
   if (!GV.hasLinkOnceLinkage() && !GV.hasAvailableExternallyLinkage() &&
       !shouldLinkOnlyNeeded())
     return;
 
   if (shouldInternalizeLinkedSymbols())
     Internalize.insert(GV.getName());
   Add(GV);
bool ModuleLinker::run() {
 
   // FIXME: Propagate Errors through to the caller instead of emitting
   // diagnostics.
   bool HasErrors = false;
   if (Error E = Mover.move(std::move(SrcM), ValuesToLink.getArrayRef(),
                            [this](GlobalValue &GV, IRMover::ValueAdder Add) {
                              addLazyFor(GV, Add);
                            },
-                           /* LinkModuleInlineAsm */ !isPerformingImport(),
-                           /* IsPerformingImport */ isPerformingImport())) {
+                           /* LinkModuleInlineAsm */ true,
+                           /* IsPerformingImport */ false)) {
     handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
       DstM.getContext().diagnose(LinkDiagnosticInfo(DS_Error, EIB.message()));
       HasErrors = true;
     });
   }
   if (HasErrors)
     return true;
 
   for (auto &P : Internalize) {
     GlobalValue *GV = DstM.getNamedValue(P.first());
     GV->setLinkage(GlobalValue::InternalLinkage);
   }
 
   return false;
 }
 
 Linker::Linker(Module &M) : Mover(M) {}
 
-bool Linker::linkInModule(std::unique_ptr<Module> Src, unsigned Flags,
-                          DenseSet<const GlobalValue *> *GlobalsToImport) {
-  ModuleLinker ModLinker(Mover, std::move(Src), Flags, GlobalsToImport);
+bool Linker::linkInModule(std::unique_ptr<Module> Src, unsigned Flags) {
+  ModuleLinker ModLinker(Mover, std::move(Src), Flags);
   return ModLinker.run();
 }
 
 //===----------------------------------------------------------------------===//
 // LinkModules entrypoint.
 //===----------------------------------------------------------------------===//
 
 /// This function links two modules together, with the resulting Dest module