1 //===-- AArch64CleanupLocalDynamicTLSPass.cpp ---------------------*- C++ -*-=//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Local-dynamic access to thread-local variables proceeds in three stages.
11 //
12 // 1. The offset of this Module's thread-local area from TPIDR_EL0 is calculated
13 // in much the same way as a general-dynamic TLS-descriptor access against
14 // the special symbol _TLS_MODULE_BASE.
15 // 2. The variable's offset from _TLS_MODULE_BASE_ is calculated using
16 // instructions with "dtprel" modifiers.
17 // 3. These two are added, together with TPIDR_EL0, to obtain the variable's
18 // true address.
19 //
20 // This is only better than general-dynamic access to the variable if two or
21 // more of the first stage TLS-descriptor calculations can be combined. This
22 // pass looks through a function and performs such combinations.
23 //
24 //===----------------------------------------------------------------------===//
25 #include "AArch64.h"
26 #include "AArch64InstrInfo.h"
27 #include "AArch64MachineFunctionInfo.h"
28 #include "llvm/CodeGen/MachineDominators.h"
29 #include "llvm/CodeGen/MachineFunction.h"
30 #include "llvm/CodeGen/MachineFunctionPass.h"
31 #include "llvm/CodeGen/MachineInstrBuilder.h"
32 #include "llvm/CodeGen/MachineRegisterInfo.h"
33 using namespace llvm;
34
35 #define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
36
37 namespace {
38 struct LDTLSCleanup : public MachineFunctionPass {
39 static char ID;
LDTLSCleanup__anonb8c24f230111::LDTLSCleanup40 LDTLSCleanup() : MachineFunctionPass(ID) {
41 initializeLDTLSCleanupPass(*PassRegistry::getPassRegistry());
42 }
43
runOnMachineFunction__anonb8c24f230111::LDTLSCleanup44 bool runOnMachineFunction(MachineFunction &MF) override {
45 if (skipFunction(MF.getFunction()))
46 return false;
47
48 AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
49 if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
50 // No point folding accesses if there isn't at least two.
51 return false;
52 }
53
54 MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
55 return VisitNode(DT->getRootNode(), 0);
56 }
57
58 // Visit the dominator subtree rooted at Node in pre-order.
59 // If TLSBaseAddrReg is non-null, then use that to replace any
60 // TLS_base_addr instructions. Otherwise, create the register
61 // when the first such instruction is seen, and then use it
62 // as we encounter more instructions.
VisitNode__anonb8c24f230111::LDTLSCleanup63 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
64 MachineBasicBlock *BB = Node->getBlock();
65 bool Changed = false;
66
67 // Traverse the current block.
68 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
69 ++I) {
70 switch (I->getOpcode()) {
71 case AArch64::TLSDESC_CALLSEQ:
72 // Make sure it's a local dynamic access.
73 if (!I->getOperand(0).isSymbol() ||
74 strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
75 break;
76
77 if (TLSBaseAddrReg)
78 I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
79 else
80 I = setRegister(*I, &TLSBaseAddrReg);
81 Changed = true;
82 break;
83 default:
84 break;
85 }
86 }
87
88 // Visit the children of this block in the dominator tree.
89 for (MachineDomTreeNode *N : *Node) {
90 Changed |= VisitNode(N, TLSBaseAddrReg);
91 }
92
93 return Changed;
94 }
95
96 // Replace the TLS_base_addr instruction I with a copy from
97 // TLSBaseAddrReg, returning the new instruction.
replaceTLSBaseAddrCall__anonb8c24f230111::LDTLSCleanup98 MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
99 unsigned TLSBaseAddrReg) {
100 MachineFunction *MF = I.getParent()->getParent();
101 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
102
103 // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
104 // code sequence assumes the address will be.
105 MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
106 TII->get(TargetOpcode::COPY), AArch64::X0)
107 .addReg(TLSBaseAddrReg);
108
109 // Erase the TLS_base_addr instruction.
110 I.eraseFromParent();
111
112 return Copy;
113 }
114
115 // Create a virtual register in *TLSBaseAddrReg, and populate it by
116 // inserting a copy instruction after I. Returns the new instruction.
setRegister__anonb8c24f230111::LDTLSCleanup117 MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
118 MachineFunction *MF = I.getParent()->getParent();
119 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
120
121 // Create a virtual register for the TLS base address.
122 MachineRegisterInfo &RegInfo = MF->getRegInfo();
123 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
124
125 // Insert a copy from X0 to TLSBaseAddrReg for later.
126 MachineInstr *Copy =
127 BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
128 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
129 .addReg(AArch64::X0);
130
131 return Copy;
132 }
133
getPassName__anonb8c24f230111::LDTLSCleanup134 StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
135
getAnalysisUsage__anonb8c24f230111::LDTLSCleanup136 void getAnalysisUsage(AnalysisUsage &AU) const override {
137 AU.setPreservesCFG();
138 AU.addRequired<MachineDominatorTree>();
139 MachineFunctionPass::getAnalysisUsage(AU);
140 }
141 };
142 }
143
144 INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
145 TLSCLEANUP_PASS_NAME, false, false)
146
147 char LDTLSCleanup::ID = 0;
createAArch64CleanupLocalDynamicTLSPass()148 FunctionPass *llvm::createAArch64CleanupLocalDynamicTLSPass() {
149 return new LDTLSCleanup();
150 }
151