1 //===- LowerEmuTLS.cpp - Add __emutls_[vt].* variables --------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This transformation is required for targets depending on libgcc style 10 // emulated thread local storage variables. For every defined TLS variable xyz, 11 // an __emutls_v.xyz is generated. If there is non-zero initialized value 12 // an __emutls_t.xyz is also generated. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #include "llvm/ADT/SmallVector.h" 17 #include "llvm/CodeGen/Passes.h" 18 #include "llvm/CodeGen/TargetLowering.h" 19 #include "llvm/CodeGen/TargetPassConfig.h" 20 #include "llvm/IR/LLVMContext.h" 21 #include "llvm/IR/Module.h" 22 #include "llvm/InitializePasses.h" 23 #include "llvm/Pass.h" 24 25 using namespace llvm; 26 27 #define DEBUG_TYPE "loweremutls" 28 29 namespace { 30 31 class LowerEmuTLS : public ModulePass { 32 public: 33 static char ID; // Pass identification, replacement for typeid 34 LowerEmuTLS() : ModulePass(ID) { 35 initializeLowerEmuTLSPass(*PassRegistry::getPassRegistry()); 36 } 37 38 bool runOnModule(Module &M) override; 39 private: 40 bool addEmuTlsVar(Module &M, const GlobalVariable *GV); 41 static void copyLinkageVisibility(Module &M, 42 const GlobalVariable *from, 43 GlobalVariable *to) { 44 to->setLinkage(from->getLinkage()); 45 to->setVisibility(from->getVisibility()); 46 if (from->hasComdat()) { 47 to->setComdat(M.getOrInsertComdat(to->getName())); 48 to->getComdat()->setSelectionKind(from->getComdat()->getSelectionKind()); 49 } 50 } 51 }; 52 } 53 54 char LowerEmuTLS::ID = 0; 55 56 INITIALIZE_PASS(LowerEmuTLS, DEBUG_TYPE, 57 "Add __emutls_[vt]. variables for emultated TLS model", false, 58 false) 59 60 ModulePass *llvm::createLowerEmuTLSPass() { return new LowerEmuTLS(); } 61 62 bool LowerEmuTLS::runOnModule(Module &M) { 63 if (skipModule(M)) 64 return false; 65 66 auto *TPC = getAnalysisIfAvailable<TargetPassConfig>(); 67 if (!TPC) 68 return false; 69 70 auto &TM = TPC->getTM<TargetMachine>(); 71 if (!TM.useEmulatedTLS()) 72 return false; 73 74 bool Changed = false; 75 SmallVector<const GlobalVariable*, 8> TlsVars; 76 for (const auto &G : M.globals()) { 77 if (G.isThreadLocal()) 78 TlsVars.append({&G}); 79 } 80 for (const auto G : TlsVars) 81 Changed |= addEmuTlsVar(M, G); 82 return Changed; 83 } 84 85 bool LowerEmuTLS::addEmuTlsVar(Module &M, const GlobalVariable *GV) { 86 LLVMContext &C = M.getContext(); 87 PointerType *VoidPtrType = Type::getInt8PtrTy(C); 88 89 std::string EmuTlsVarName = ("__emutls_v." + GV->getName()).str(); 90 GlobalVariable *EmuTlsVar = M.getNamedGlobal(EmuTlsVarName); 91 if (EmuTlsVar) 92 return false; // It has been added before. 93 94 const DataLayout &DL = M.getDataLayout(); 95 Constant *NullPtr = ConstantPointerNull::get(VoidPtrType); 96 97 // Get non-zero initializer from GV's initializer. 98 const Constant *InitValue = nullptr; 99 if (GV->hasInitializer()) { 100 InitValue = GV->getInitializer(); 101 const ConstantInt *InitIntValue = dyn_cast<ConstantInt>(InitValue); 102 // When GV's init value is all 0, omit the EmuTlsTmplVar and let 103 // the emutls library function to reset newly allocated TLS variables. 104 if (isa<ConstantAggregateZero>(InitValue) || 105 (InitIntValue && InitIntValue->isZero())) 106 InitValue = nullptr; 107 } 108 109 // Create the __emutls_v. symbol, whose type has 4 fields: 110 // word size; // size of GV in bytes 111 // word align; // alignment of GV 112 // void *ptr; // initialized to 0; set at run time per thread. 113 // void *templ; // 0 or point to __emutls_t.* 114 // sizeof(word) should be the same as sizeof(void*) on target. 115 IntegerType *WordType = DL.getIntPtrType(C); 116 PointerType *InitPtrType = InitValue ? 117 PointerType::getUnqual(InitValue->getType()) : VoidPtrType; 118 Type *ElementTypes[4] = {WordType, WordType, VoidPtrType, InitPtrType}; 119 ArrayRef<Type*> ElementTypeArray(ElementTypes, 4); 120 StructType *EmuTlsVarType = StructType::create(ElementTypeArray); 121 EmuTlsVar = cast<GlobalVariable>( 122 M.getOrInsertGlobal(EmuTlsVarName, EmuTlsVarType)); 123 copyLinkageVisibility(M, GV, EmuTlsVar); 124 125 // Define "__emutls_t.*" and "__emutls_v.*" only if GV is defined. 126 if (!GV->hasInitializer()) 127 return true; 128 129 Type *GVType = GV->getValueType(); 130 unsigned GVAlignment = GV->getAlignment(); 131 if (!GVAlignment) { 132 // When LLVM IL declares a variable without alignment, use 133 // the ABI default alignment for the type. 134 GVAlignment = DL.getABITypeAlignment(GVType); 135 } 136 137 // Define "__emutls_t.*" if there is InitValue 138 GlobalVariable *EmuTlsTmplVar = nullptr; 139 if (InitValue) { 140 std::string EmuTlsTmplName = ("__emutls_t." + GV->getName()).str(); 141 EmuTlsTmplVar = dyn_cast_or_null<GlobalVariable>( 142 M.getOrInsertGlobal(EmuTlsTmplName, GVType)); 143 assert(EmuTlsTmplVar && "Failed to create emualted TLS initializer"); 144 EmuTlsTmplVar->setConstant(true); 145 EmuTlsTmplVar->setInitializer(const_cast<Constant*>(InitValue)); 146 EmuTlsTmplVar->setAlignment(Align(GVAlignment)); 147 copyLinkageVisibility(M, GV, EmuTlsTmplVar); 148 } 149 150 // Define "__emutls_v.*" with initializer and alignment. 151 Constant *ElementValues[4] = { 152 ConstantInt::get(WordType, DL.getTypeStoreSize(GVType)), 153 ConstantInt::get(WordType, GVAlignment), 154 NullPtr, EmuTlsTmplVar ? EmuTlsTmplVar : NullPtr 155 }; 156 ArrayRef<Constant*> ElementValueArray(ElementValues, 4); 157 EmuTlsVar->setInitializer( 158 ConstantStruct::get(EmuTlsVarType, ElementValueArray)); 159 Align MaxAlignment(std::max(DL.getABITypeAlignment(WordType), 160 DL.getABITypeAlignment(VoidPtrType))); 161 EmuTlsVar->setAlignment(MaxAlignment); 162 return true; 163 } 164