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