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//===- LowerEmuTLS.cpp - Add __emutls_[vt].* variables --------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This transformation is required for targets depending on libgcc style
// emulated thread local storage variables. For every defined TLS variable xyz,
// an is generated. If there is non-zero initialized value
// an is also generated.
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "loweremutls"
namespace {
class LowerEmuTLS : public ModulePass {
static char ID; // Pass identification, replacement for typeid
LowerEmuTLS() : ModulePass(ID) {
bool runOnModule(Module &M) override;
bool addEmuTlsVar(Module &M, const GlobalVariable *GV);
static void copyLinkageVisibility(Module &M,
const GlobalVariable *from,
GlobalVariable *to) {
if (from->hasComdat()) {
char LowerEmuTLS::ID = 0;
"Add __emutls_[vt]. variables for emultated TLS model", false,
ModulePass *llvm::createLowerEmuTLSPass() { return new LowerEmuTLS(); }
bool LowerEmuTLS::runOnModule(Module &M) {
if (skipModule(M))
return false;
auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
if (!TPC)
return false;
auto &TM = TPC->getTM<TargetMachine>();
if (!TM.useEmulatedTLS())
return false;
bool Changed = false;
SmallVector<const GlobalVariable*, 8> TlsVars;
for (const auto &G : M.globals()) {
if (G.isThreadLocal())
for (const auto G : TlsVars)
Changed |= addEmuTlsVar(M, G);
return Changed;
bool LowerEmuTLS::addEmuTlsVar(Module &M, const GlobalVariable *GV) {
LLVMContext &C = M.getContext();
PointerType *VoidPtrType = Type::getInt8PtrTy(C);
std::string EmuTlsVarName = ("__emutls_v." + GV->getName()).str();
GlobalVariable *EmuTlsVar = M.getNamedGlobal(EmuTlsVarName);
if (EmuTlsVar)
return false; // It has been added before.
const DataLayout &DL = M.getDataLayout();
Constant *NullPtr = ConstantPointerNull::get(VoidPtrType);
// Get non-zero initializer from GV's initializer.
const Constant *InitValue = nullptr;
if (GV->hasInitializer()) {
InitValue = GV->getInitializer();
const ConstantInt *InitIntValue = dyn_cast<ConstantInt>(InitValue);
// When GV's init value is all 0, omit the EmuTlsTmplVar and let
// the emutls library function to reset newly allocated TLS variables.
if (isa<ConstantAggregateZero>(InitValue) ||
(InitIntValue && InitIntValue->isZero()))
InitValue = nullptr;
// Create the __emutls_v. symbol, whose type has 4 fields:
// word size; // size of GV in bytes
// word align; // alignment of GV
// void *ptr; // initialized to 0; set at run time per thread.
// void *templ; // 0 or point to __emutls_t.*
// sizeof(word) should be the same as sizeof(void*) on target.
IntegerType *WordType = DL.getIntPtrType(C);
PointerType *InitPtrType = InitValue ?
PointerType::getUnqual(InitValue->getType()) : VoidPtrType;
Type *ElementTypes[4] = {WordType, WordType, VoidPtrType, InitPtrType};
ArrayRef<Type*> ElementTypeArray(ElementTypes, 4);
StructType *EmuTlsVarType = StructType::create(ElementTypeArray);
EmuTlsVar = cast<GlobalVariable>(
M.getOrInsertGlobal(EmuTlsVarName, EmuTlsVarType));
copyLinkageVisibility(M, GV, EmuTlsVar);
// Define "__emutls_t.*" and "__emutls_v.*" only if GV is defined.
if (!GV->hasInitializer())
return true;
Type *GVType = GV->getValueType();
Align GVAlignment = DL.getValueOrABITypeAlignment(GV->getAlign(), GVType);
// Define "__emutls_t.*" if there is InitValue
GlobalVariable *EmuTlsTmplVar = nullptr;
if (InitValue) {
std::string EmuTlsTmplName = ("__emutls_t." + GV->getName()).str();
EmuTlsTmplVar = dyn_cast_or_null<GlobalVariable>(
M.getOrInsertGlobal(EmuTlsTmplName, GVType));
assert(EmuTlsTmplVar && "Failed to create emualted TLS initializer");
copyLinkageVisibility(M, GV, EmuTlsTmplVar);
// Define "__emutls_v.*" with initializer and alignment.
Constant *ElementValues[4] = {
ConstantInt::get(WordType, DL.getTypeStoreSize(GVType)),
ConstantInt::get(WordType, GVAlignment.value()), NullPtr,
EmuTlsTmplVar ? EmuTlsTmplVar : NullPtr};
ArrayRef<Constant*> ElementValueArray(ElementValues, 4);
ConstantStruct::get(EmuTlsVarType, ElementValueArray));
Align MaxAlignment =
std::max(DL.getABITypeAlign(WordType), DL.getABITypeAlign(VoidPtrType));
return true;