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/CodeGen/LowerEmuTLS.h"
  17 #include "llvm/ADT/SmallVector.h"
  18 #include "llvm/Analysis/GlobalsModRef.h"
  19 #include "llvm/Analysis/ModuleSummaryAnalysis.h"
  20 #include "llvm/Analysis/StackSafetyAnalysis.h"
  21 #include "llvm/CodeGen/Passes.h"
  22 #include "llvm/CodeGen/TargetPassConfig.h"
  23 #include "llvm/IR/Constants.h"
  24 #include "llvm/IR/Module.h"
  25 #include "llvm/InitializePasses.h"
  26 #include "llvm/Pass.h"
  27 #include "llvm/Target/TargetMachine.h"
  28
  29 using namespace llvm;
  30
  31 #define DEBUG_TYPE "lower-emutls"
  32
  33 namespace {
  34
  35 class LowerEmuTLS : public ModulePass {
  36 public:
  37   static char ID; // Pass identification, replacement for typeid
  38   LowerEmuTLS() : ModulePass(ID) {
  39     initializeLowerEmuTLSPass(*PassRegistry::getPassRegistry());
  40   }
  41
  42   bool runOnModule(Module &M) override;
  43 };
  44 }
  45
  46 static bool addEmuTlsVar(Module &M, const GlobalVariable *GV);
  47
  48 static void copyLinkageVisibility(Module &M, const GlobalVariable *from,
  49                                   GlobalVariable *to) {
  50   to->setLinkage(from->getLinkage());
  51   to->setVisibility(from->getVisibility());
  52   to->setDSOLocal(from->isDSOLocal());
  53   if (from->hasComdat()) {
  54     to->setComdat(M.getOrInsertComdat(to->getName()));
  55     to->getComdat()->setSelectionKind(from->getComdat()->getSelectionKind());
  56   }
  57 }
  58
  59 PreservedAnalyses LowerEmuTLSPass::run(Module &M, ModuleAnalysisManager &MAM) {
  60   bool Changed = false;
  61   SmallVector<const GlobalVariable *, 8> TlsVars;
  62   for (const auto &G : M.globals()) {
  63     if (G.isThreadLocal())
  64       TlsVars.push_back(&G);
  65   }
  66   for (const auto *G : TlsVars)
  67     Changed |= addEmuTlsVar(M, G);
  68
  69   if (!Changed)
  70     return PreservedAnalyses::all();
  71   PreservedAnalyses PA = PreservedAnalyses::all();
  72   PA.abandon<GlobalsAA>();
  73   PA.abandon<ModuleSummaryIndexAnalysis>();
  74   PA.abandon<StackSafetyGlobalAnalysis>();
  75   return PA;
  76 }
  77
  78 char LowerEmuTLS::ID = 0;
  79
  80 INITIALIZE_PASS(LowerEmuTLS, DEBUG_TYPE,
  81                 "Add __emutls_[vt]. variables for emultated TLS model", false,
  82                 false)
  83
  84 ModulePass *llvm::createLowerEmuTLSPass() { return new LowerEmuTLS(); }
  85
  86 bool LowerEmuTLS::runOnModule(Module &M) {
  87   if (skipModule(M))
  88     return false;
  89
  90   auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
  91   if (!TPC)
  92     return false;
  93
  94   auto &TM = TPC->getTM<TargetMachine>();
  95   if (!TM.useEmulatedTLS())
  96     return false;
  97
  98   bool Changed = false;
  99   SmallVector<const GlobalVariable*, 8> TlsVars;
 100   for (const auto &G : M.globals()) {
 101     if (G.isThreadLocal())
 102       TlsVars.append({&G});
 103   }
 104   for (const auto *const G : TlsVars)
 105     Changed |= addEmuTlsVar(M, G);
 106   return Changed;
 107 }
 108
 109 bool addEmuTlsVar(Module &M, const GlobalVariable *GV) {
 110   LLVMContext &C = M.getContext();
 111   PointerType *VoidPtrType = PointerType::getUnqual(C);
 112
 113   std::string EmuTlsVarName = ("__emutls_v." + GV->getName()).str();
 114   GlobalVariable *EmuTlsVar = M.getNamedGlobal(EmuTlsVarName);
 115   if (EmuTlsVar)
 116     return false;  // It has been added before.
 117
 118   const DataLayout &DL = M.getDataLayout();
 119   Constant *NullPtr = ConstantPointerNull::get(VoidPtrType);
 120
 121   // Get non-zero initializer from GV's initializer.
 122   const Constant *InitValue = nullptr;
 123   if (GV->hasInitializer()) {
 124     InitValue = GV->getInitializer();
 125     const ConstantInt *InitIntValue = dyn_cast<ConstantInt>(InitValue);
 126     // When GV's init value is all 0, omit the EmuTlsTmplVar and let
 127     // the emutls library function to reset newly allocated TLS variables.
 128     if (isa<ConstantAggregateZero>(InitValue) ||
 129         (InitIntValue && InitIntValue->isZero()))
 130       InitValue = nullptr;
 131   }
 132
 133   // Create the __emutls_v. symbol, whose type has 4 fields:
 134   //     word size;   // size of GV in bytes
 135   //     word align;  // alignment of GV
 136   //     void *ptr;   // initialized to 0; set at run time per thread.
 137   //     void *templ; // 0 or point to __emutls_t.*
 138   // sizeof(word) should be the same as sizeof(void*) on target.
 139   IntegerType *WordType = DL.getIntPtrType(C);
 140   PointerType *InitPtrType = PointerType::getUnqual(C);
 141   Type *ElementTypes[4] = {WordType, WordType, VoidPtrType, InitPtrType};
 142   StructType *EmuTlsVarType = StructType::create(ElementTypes);
 143   EmuTlsVar = cast<GlobalVariable>(
 144       M.getOrInsertGlobal(EmuTlsVarName, EmuTlsVarType));
 145   copyLinkageVisibility(M, GV, EmuTlsVar);
 146
 147   // Define "__emutls_t.*" and "__emutls_v.*" only if GV is defined.
 148   if (!GV->hasInitializer())
 149     return true;
 150
 151   Type *GVType = GV->getValueType();
 152   Align GVAlignment = DL.getValueOrABITypeAlignment(GV->getAlign(), GVType);
 153
 154   // Define "__emutls_t.*" if there is InitValue
 155   GlobalVariable *EmuTlsTmplVar = nullptr;
 156   if (InitValue) {
 157     std::string EmuTlsTmplName = ("__emutls_t." + GV->getName()).str();
 158     EmuTlsTmplVar = dyn_cast_or_null<GlobalVariable>(
 159         M.getOrInsertGlobal(EmuTlsTmplName, GVType));
 160     assert(EmuTlsTmplVar && "Failed to create emualted TLS initializer");
 161     EmuTlsTmplVar->setConstant(true);
 162     EmuTlsTmplVar->setInitializer(const_cast<Constant*>(InitValue));
 163     EmuTlsTmplVar->setAlignment(GVAlignment);
 164     copyLinkageVisibility(M, GV, EmuTlsTmplVar);
 165   }
 166
 167   // Define "__emutls_v.*" with initializer and alignment.
 168   Constant *ElementValues[4] = {
 169       ConstantInt::get(WordType, DL.getTypeStoreSize(GVType)),
 170       ConstantInt::get(WordType, GVAlignment.value()), NullPtr,
 171       EmuTlsTmplVar ? EmuTlsTmplVar : NullPtr};
 172   EmuTlsVar->setInitializer(ConstantStruct::get(EmuTlsVarType, ElementValues));
 173   Align MaxAlignment =
 174       std::max(DL.getABITypeAlign(WordType), DL.getABITypeAlign(VoidPtrType));
 175   EmuTlsVar->setAlignment(MaxAlignment);
 176   return true;
 177 }