llvm/lib/CodeGen/LowerEmuTLS.cpp

   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/TargetPassConfig.h"
  19 #include "llvm/IR/Constants.h"
  20 #include "llvm/IR/LLVMContext.h"
  21 #include "llvm/IR/Module.h"
  22 #include "llvm/InitializePasses.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/Target/TargetMachine.h"
  25
  26 using namespace llvm;
  27
  28 #define DEBUG_TYPE "loweremutls"
  29
  30 namespace {
  31
  32 class LowerEmuTLS : public ModulePass {
  33 public:
  34   static char ID; // Pass identification, replacement for typeid
  35   LowerEmuTLS() : ModulePass(ID) {
  36     initializeLowerEmuTLSPass(*PassRegistry::getPassRegistry());
  37   }
  38
  39   bool runOnModule(Module &M) override;
  40 private:
  41   bool addEmuTlsVar(Module &M, const GlobalVariable *GV);
  42   static void copyLinkageVisibility(Module &M,
  43                                     const GlobalVariable *from,
  44                                     GlobalVariable *to) {
  45     to->setLinkage(from->getLinkage());
  46     to->setVisibility(from->getVisibility());
  47     to->setDSOLocal(from->isDSOLocal());
  48     if (from->hasComdat()) {
  49       to->setComdat(M.getOrInsertComdat(to->getName()));
  50       to->getComdat()->setSelectionKind(from->getComdat()->getSelectionKind());
  51     }
  52   }
  53 };
  54 }
  55
  56 char LowerEmuTLS::ID = 0;
  57
  58 INITIALIZE_PASS(LowerEmuTLS, DEBUG_TYPE,
  59                 "Add __emutls_[vt]. variables for emultated TLS model", false,
  60                 false)
  61
  62 ModulePass *llvm::createLowerEmuTLSPass() { return new LowerEmuTLS(); }
  63
  64 bool LowerEmuTLS::runOnModule(Module &M) {
  65   if (skipModule(M))
  66     return false;
  67
  68   auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
  69   if (!TPC)
  70     return false;
  71
  72   auto &TM = TPC->getTM<TargetMachine>();
  73   if (!TM.useEmulatedTLS())
  74     return false;
  75
  76   bool Changed = false;
  77   SmallVector<const GlobalVariable*, 8> TlsVars;
  78   for (const auto &G : M.globals()) {
  79     if (G.isThreadLocal())
  80       TlsVars.append({&G});
  81   }
  82   for (const auto G : TlsVars)
  83     Changed |= addEmuTlsVar(M, G);
  84   return Changed;
  85 }
  86
  87 bool LowerEmuTLS::addEmuTlsVar(Module &M, const GlobalVariable *GV) {
  88   LLVMContext &C = M.getContext();
  89   PointerType *VoidPtrType = Type::getInt8PtrTy(C);
  90
  91   std::string EmuTlsVarName = ("__emutls_v." + GV->getName()).str();
  92   GlobalVariable *EmuTlsVar = M.getNamedGlobal(EmuTlsVarName);
  93   if (EmuTlsVar)
  94     return false;  // It has been added before.
  95
  96   const DataLayout &DL = M.getDataLayout();
  97   Constant *NullPtr = ConstantPointerNull::get(VoidPtrType);
  98
  99   // Get non-zero initializer from GV's initializer.
 100   const Constant *InitValue = nullptr;
 101   if (GV->hasInitializer()) {
 102     InitValue = GV->getInitializer();
 103     const ConstantInt *InitIntValue = dyn_cast<ConstantInt>(InitValue);
 104     // When GV's init value is all 0, omit the EmuTlsTmplVar and let
 105     // the emutls library function to reset newly allocated TLS variables.
 106     if (isa<ConstantAggregateZero>(InitValue) ||
 107         (InitIntValue && InitIntValue->isZero()))
 108       InitValue = nullptr;
 109   }
 110
 111   // Create the __emutls_v. symbol, whose type has 4 fields:
 112   //     word size;   // size of GV in bytes
 113   //     word align;  // alignment of GV
 114   //     void *ptr;   // initialized to 0; set at run time per thread.
 115   //     void *templ; // 0 or point to __emutls_t.*
 116   // sizeof(word) should be the same as sizeof(void*) on target.
 117   IntegerType *WordType = DL.getIntPtrType(C);
 118   PointerType *InitPtrType = InitValue ?
 119       PointerType::getUnqual(InitValue->getType()) : VoidPtrType;
 120   Type *ElementTypes[4] = {WordType, WordType, VoidPtrType, InitPtrType};
 121   ArrayRef<Type*> ElementTypeArray(ElementTypes, 4);
 122   StructType *EmuTlsVarType = StructType::create(ElementTypeArray);
 123   EmuTlsVar = cast<GlobalVariable>(
 124       M.getOrInsertGlobal(EmuTlsVarName, EmuTlsVarType));
 125   copyLinkageVisibility(M, GV, EmuTlsVar);
 126
 127   // Define "__emutls_t.*" and "__emutls_v.*" only if GV is defined.
 128   if (!GV->hasInitializer())
 129     return true;
 130
 131   Type *GVType = GV->getValueType();
 132   Align GVAlignment = DL.getValueOrABITypeAlignment(GV->getAlign(), GVType);
 133
 134   // Define "__emutls_t.*" if there is InitValue
 135   GlobalVariable *EmuTlsTmplVar = nullptr;
 136   if (InitValue) {
 137     std::string EmuTlsTmplName = ("__emutls_t." + GV->getName()).str();
 138     EmuTlsTmplVar = dyn_cast_or_null<GlobalVariable>(
 139         M.getOrInsertGlobal(EmuTlsTmplName, GVType));
 140     assert(EmuTlsTmplVar && "Failed to create emualted TLS initializer");
 141     EmuTlsTmplVar->setConstant(true);
 142     EmuTlsTmplVar->setInitializer(const_cast<Constant*>(InitValue));
 143     EmuTlsTmplVar->setAlignment(GVAlignment);
 144     copyLinkageVisibility(M, GV, EmuTlsTmplVar);
 145   }
 146
 147   // Define "__emutls_v.*" with initializer and alignment.
 148   Constant *ElementValues[4] = {
 149       ConstantInt::get(WordType, DL.getTypeStoreSize(GVType)),
 150       ConstantInt::get(WordType, GVAlignment.value()), NullPtr,
 151       EmuTlsTmplVar ? EmuTlsTmplVar : NullPtr};
 152   ArrayRef<Constant*> ElementValueArray(ElementValues, 4);
 153   EmuTlsVar->setInitializer(
 154       ConstantStruct::get(EmuTlsVarType, ElementValueArray));
 155   Align MaxAlignment =
 156       std::max(DL.getABITypeAlign(WordType), DL.getABITypeAlign(VoidPtrType));
 157   EmuTlsVar->setAlignment(MaxAlignment);
 158   return true;
 159 }