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
29using namespace llvm;
30
31#define DEBUG_TYPE "lower-emutls"
32
33namespace {
34
35class LowerEmuTLS : public ModulePass {
36public:
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
46static bool addEmuTlsVar(Module &M, const GlobalVariable *GV);
47
48static 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(Name: to->getName()));
55 to->getComdat()->setSelectionKind(from->getComdat()->getSelectionKind());
56 }
57}
58
59PreservedAnalyses 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(Elt: &G);
65 }
66 for (const auto *G : TlsVars)
67 Changed |= addEmuTlsVar(M, GV: 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
78char LowerEmuTLS::ID = 0;
79
80INITIALIZE_PASS(LowerEmuTLS, DEBUG_TYPE,
81 "Add __emutls_[vt]. variables for emultated TLS model", false,
82 false)
83
84ModulePass *llvm::createLowerEmuTLSPass() { return new LowerEmuTLS(); }
85
86bool 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(IL: {&G});
103 }
104 for (const auto *const G : TlsVars)
105 Changed |= addEmuTlsVar(M, GV: G);
106 return Changed;
107}
108
109bool 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(Name: EmuTlsVarName);
115 if (EmuTlsVar)
116 return false; // It has been added before.
117
118 const DataLayout &DL = M.getDataLayout();
119 Constant *NullPtr = ConstantPointerNull::get(T: 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>(Val: 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>(Val: 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(Elements: ElementTypes);
143 EmuTlsVar = M.getOrInsertGlobal(Name: EmuTlsVarName, Ty: EmuTlsVarType);
144 copyLinkageVisibility(M, from: GV, to: EmuTlsVar);
145
146 // Define "__emutls_t.*" and "__emutls_v.*" only if GV is defined.
147 if (!GV->hasInitializer())
148 return true;
149
150 Type *GVType = GV->getValueType();
151 Align GVAlignment = DL.getValueOrABITypeAlignment(Alignment: GV->getAlign(), Ty: GVType);
152
153 // Define "__emutls_t.*" if there is InitValue
154 GlobalVariable *EmuTlsTmplVar = nullptr;
155 if (InitValue) {
156 std::string EmuTlsTmplName = ("__emutls_t." + GV->getName()).str();
157 EmuTlsTmplVar = M.getOrInsertGlobal(Name: EmuTlsTmplName, Ty: GVType);
158 assert(EmuTlsTmplVar && "Failed to create emualted TLS initializer");
159 EmuTlsTmplVar->setConstant(true);
160 EmuTlsTmplVar->setInitializer(const_cast<Constant*>(InitValue));
161 EmuTlsTmplVar->setAlignment(GVAlignment);
162 copyLinkageVisibility(M, from: GV, to: EmuTlsTmplVar);
163 }
164
165 // Define "__emutls_v.*" with initializer and alignment.
166 Constant *ElementValues[4] = {
167 ConstantInt::get(Ty: WordType, V: DL.getTypeStoreSize(Ty: GVType)),
168 ConstantInt::get(Ty: WordType, V: GVAlignment.value()), NullPtr,
169 EmuTlsTmplVar ? EmuTlsTmplVar : NullPtr};
170 EmuTlsVar->setInitializer(ConstantStruct::get(T: EmuTlsVarType, V: ElementValues));
171 Align MaxAlignment =
172 std::max(a: DL.getABITypeAlign(Ty: WordType), b: DL.getABITypeAlign(Ty: VoidPtrType));
173 EmuTlsVar->setAlignment(MaxAlignment);
174 return true;
175}
176