Index: include/llvm/Linker/Linker.h =================================================================== --- include/llvm/Linker/Linker.h +++ include/llvm/Linker/Linker.h @@ -29,7 +29,10 @@ None = 0, OverrideFromSrc = (1 << 0), LinkOnlyNeeded = (1 << 1), - InternalizeLinkedSymbols = (1 << 2) + InternalizeLinkedSymbols = (1 << 2), + /// Don't force link referenced linkonce definitions, import declaration. + DontForceLinkLinkonceODR = (1 << 3) + }; Linker(Module &M); Index: include/llvm/Transforms/IPO/FunctionImport.h =================================================================== --- include/llvm/Transforms/IPO/FunctionImport.h +++ include/llvm/Transforms/IPO/FunctionImport.h @@ -48,7 +48,11 @@ : Index(Index), ModuleLoader(ModuleLoader) {} /// Import functions in Module \p M based on the supplied import list. - bool importFunctions(Module &M, const ImportMapTy &ImportList); + /// \p ForceImportReferencedDiscardableSymbols will set the ModuleLinker in + /// a mode where referenced discarable symbols in the source modules will be + /// imported as well even if they are not present in the ImportList. + bool importFunctions(Module &M, const ImportMapTy &ImportList, + bool ForceImportReferencedDiscardableSymbols = false); private: /// The summaries index used to trigger importing. Index: lib/Linker/LinkModules.cpp =================================================================== --- lib/Linker/LinkModules.cpp +++ lib/Linker/LinkModules.cpp @@ -45,6 +45,9 @@ /// to Add. void addLazyFor(GlobalValue &GV, IRMover::ValueAdder Add); + bool shouldLinkReferencedLinkOnce() { + return !(Flags & Linker::DontForceLinkLinkonceODR); + } bool shouldOverrideFromSrc() { return Flags & Linker::OverrideFromSrc; } bool shouldLinkOnlyNeeded() { return Flags & Linker::LinkOnlyNeeded; } bool shouldInternalizeLinkedSymbols() { @@ -413,6 +416,12 @@ } void ModuleLinker::addLazyFor(GlobalValue &GV, 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()) return; Index: lib/Transforms/IPO/FunctionImport.cpp =================================================================== --- lib/Transforms/IPO/FunctionImport.cpp +++ lib/Transforms/IPO/FunctionImport.cpp @@ -49,6 +49,12 @@ static cl::opt PrintImports("print-imports", cl::init(false), cl::Hidden, cl::desc("Print imported functions")); +// Temporary allows the function import pass to disable always linking +// referenced discardable symbols. +static cl::opt + DontForceImportReferencedDiscardableSymbols("disable-force-link-odr", + cl::init(false), cl::Hidden); + // Load lazily a module from \p FileName in \p Context. static std::unique_ptr loadFile(const std::string &FileName, LLVMContext &Context) { @@ -327,7 +333,8 @@ // index. // bool FunctionImporter::importFunctions( - Module &DestModule, const FunctionImporter::ImportMapTy &ImportList) { + Module &DestModule, const FunctionImporter::ImportMapTy &ImportList, + bool ForceImportReferencedDiscardableSymbols) { DEBUG(dbgs() << "Starting import for Module " << DestModule.getModuleIdentifier() << "\n"); unsigned ImportedCount = 0; @@ -420,8 +427,12 @@ << " from " << SrcModule->getSourceFileName() << "\n"; } - if (TheLinker.linkInModule(std::move(SrcModule), Linker::Flags::None, - &GlobalsToImport)) + // Instruct the linker that the client will take care of linkonce resolution + unsigned Flags = Linker::Flags::None; + if (!ForceImportReferencedDiscardableSymbols) + Flags |= Linker::Flags::DontForceLinkLinkonceODR; + + if (TheLinker.linkInModule(std::move(SrcModule), Flags, &GlobalsToImport)) report_fatal_error("Function Import: link error"); ImportedCount += GlobalsToImport.size(); @@ -523,7 +534,8 @@ return loadFile(Identifier, M.getContext()); }; FunctionImporter Importer(*Index, ModuleLoader); - return Importer.importFunctions(M, ImportList); + return Importer.importFunctions( + M, ImportList, !DontForceImportReferencedDiscardableSymbols); } }; } // anonymous namespace Index: test/Linker/funcimport2.ll =================================================================== --- test/Linker/funcimport2.ll +++ test/Linker/funcimport2.ll @@ -3,7 +3,7 @@ ; RUN: llvm-lto -thinlto -o %t3 %t1.bc %t2.bc ; RUN: llvm-link -import=bar:%t2.bc %t1.bc -summary-index=%t3.thinlto.bc -S | FileCheck %s -; CHECK: define linkonce_odr hidden void @foo() { +; CHECK: define available_externally hidden void @foo() { define available_externally hidden void @foo() { ret void } Index: test/Transforms/FunctionImport/Inputs/funcimport.ll =================================================================== --- test/Transforms/FunctionImport/Inputs/funcimport.ll +++ test/Transforms/FunctionImport/Inputs/funcimport.ll @@ -99,4 +99,46 @@ ret void } +define void @referencelargelinkonce() #0 { +entry: + call void @linkonceodr() + ret void +} + +; A large enough linkonce_odr function that should never be imported +define linkonce_odr void @linkonceodr() #0 { +entry: + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + call void @globalfunc2() + ret void +} + Index: test/Transforms/FunctionImport/funcimport.ll =================================================================== --- test/Transforms/FunctionImport/funcimport.ll +++ test/Transforms/FunctionImport/funcimport.ll @@ -4,12 +4,12 @@ ; RUN: llvm-lto -thinlto -print-summary-global-ids -o %t3 %t.bc %t2.bc 2>&1 | FileCheck %s --check-prefix=GUID ; Do the import now -; RUN: opt -function-import -stats -print-imports -summary-file %t3.thinlto.bc %t.bc -S 2>&1 | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIMDEF +; RUN: opt -disable-force-link-odr -function-import -stats -print-imports -summary-file %t3.thinlto.bc %t.bc -S 2>&1 | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIMDEF ; "-stats" requires +Asserts. ; REQUIRES: asserts ; Test import with smaller instruction limit -; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=5 -S | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIM5 +; RUN: opt -disable-force-link-odr -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=5 -S | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIM5 ; INSTLIM5-NOT: @staticfunc.llvm. define i32 @main() #0 { @@ -23,6 +23,7 @@ call void (...) @setfuncptr() call void (...) @callfuncptr() call void (...) @weakfunc() + call void (...) @referencelargelinkonce() ret i32 0 } @@ -78,6 +79,12 @@ ; CHECK-DAG: %0 = load void ()*, void ()** @P.llvm. ; CHECK-DAG: store void ()* @staticfunc2.llvm.{{.*}}, void ()** @P.llvm. +; Ensure that @referencelargelinkonce definition is pulled in, but later we +; also check that the linkonceodr function is not. +; CHECK-DAG: define available_externally void @referencelargelinkonce() +; INSTLIM5-DAG: declare void @linkonceodr() +declare void @referencelargelinkonce(...) + ; Won't import weak func ; CHECK-DAG: declare void @weakfunc(...) declare void @weakfunc(...) #1 @@ -87,7 +94,7 @@ ; INSTLIM5-DAG: declare hidden void @funcwithpersonality.llvm.{{.*}}() ; INSTLIMDEF-DAG: Import globalfunc2 -; INSTLIMDEF-DAG: 11 function-import - Number of functions imported +; INSTLIMDEF-DAG: 13 function-import - Number of functions imported ; The actual GUID values will depend on path to test. ; GUID-DAG: GUID {{.*}} is weakalias Index: tools/llvm-link/llvm-link.cpp =================================================================== --- tools/llvm-link/llvm-link.cpp +++ tools/llvm-link/llvm-link.cpp @@ -276,8 +276,10 @@ if (renameModuleForThinLTO(*SrcModule, *Index, &GlobalsToImport)) return true; - if (L.linkInModule(std::move(SrcModule), Linker::Flags::None, - &GlobalsToImport)) + // Instruct the linker to not automatically import linkonce defintion. + unsigned Flags = Linker::Flags::DontForceLinkLinkonceODR; + + if (L.linkInModule(std::move(SrcModule), Flags, &GlobalsToImport)) return false; }