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 "AArch64TargetMachine.h"
29 #include "llvm/CodeGen/MachineDominators.h"
30 #include "llvm/CodeGen/MachineFunction.h"
31 #include "llvm/CodeGen/MachineFunctionPass.h"
32 #include "llvm/CodeGen/MachineInstrBuilder.h"
33 #include "llvm/CodeGen/MachineRegisterInfo.h"
34 using namespace llvm;
35
36 namespace {
37 struct LDTLSCleanup : public MachineFunctionPass {
38 static char ID;
LDTLSCleanup__anonfdaa28eb0111::LDTLSCleanup39 LDTLSCleanup() : MachineFunctionPass(ID) {}
40
runOnMachineFunction__anonfdaa28eb0111::LDTLSCleanup41 bool runOnMachineFunction(MachineFunction &MF) override {
42 AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
43 if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
44 // No point folding accesses if there isn't at least two.
45 return false;
46 }
47
48 MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
49 return VisitNode(DT->getRootNode(), 0);
50 }
51
52 // Visit the dominator subtree rooted at Node in pre-order.
53 // If TLSBaseAddrReg is non-null, then use that to replace any
54 // TLS_base_addr instructions. Otherwise, create the register
55 // when the first such instruction is seen, and then use it
56 // as we encounter more instructions.
VisitNode__anonfdaa28eb0111::LDTLSCleanup57 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
58 MachineBasicBlock *BB = Node->getBlock();
59 bool Changed = false;
60
61 // Traverse the current block.
62 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
63 ++I) {
64 switch (I->getOpcode()) {
65 case AArch64::TLSDESC_CALLSEQ:
66 // Make sure it's a local dynamic access.
67 if (!I->getOperand(0).isSymbol() ||
68 strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
69 break;
70
71 if (TLSBaseAddrReg)
72 I = replaceTLSBaseAddrCall(I, TLSBaseAddrReg);
73 else
74 I = setRegister(I, &TLSBaseAddrReg);
75 Changed = true;
76 break;
77 default:
78 break;
79 }
80 }
81
82 // Visit the children of this block in the dominator tree.
83 for (MachineDomTreeNode *N : *Node) {
84 Changed |= VisitNode(N, TLSBaseAddrReg);
85 }
86
87 return Changed;
88 }
89
90 // Replace the TLS_base_addr instruction I with a copy from
91 // TLSBaseAddrReg, returning the new instruction.
replaceTLSBaseAddrCall__anonfdaa28eb0111::LDTLSCleanup92 MachineInstr *replaceTLSBaseAddrCall(MachineInstr *I,
93 unsigned TLSBaseAddrReg) {
94 MachineFunction *MF = I->getParent()->getParent();
95 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
96
97 // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
98 // code sequence assumes the address will be.
99 MachineInstr *Copy = BuildMI(*I->getParent(), I, I->getDebugLoc(),
100 TII->get(TargetOpcode::COPY),
101 AArch64::X0).addReg(TLSBaseAddrReg);
102
103 // Erase the TLS_base_addr instruction.
104 I->eraseFromParent();
105
106 return Copy;
107 }
108
109 // Create a virtal register in *TLSBaseAddrReg, and populate it by
110 // inserting a copy instruction after I. Returns the new instruction.
setRegister__anonfdaa28eb0111::LDTLSCleanup111 MachineInstr *setRegister(MachineInstr *I, unsigned *TLSBaseAddrReg) {
112 MachineFunction *MF = I->getParent()->getParent();
113 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
114
115 // Create a virtual register for the TLS base address.
116 MachineRegisterInfo &RegInfo = MF->getRegInfo();
117 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
118
119 // Insert a copy from X0 to TLSBaseAddrReg for later.
120 MachineInstr *Next = I->getNextNode();
121 MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(),
122 TII->get(TargetOpcode::COPY),
123 *TLSBaseAddrReg).addReg(AArch64::X0);
124
125 return Copy;
126 }
127
getPassName__anonfdaa28eb0111::LDTLSCleanup128 const char *getPassName() const override {
129 return "Local Dynamic TLS Access Clean-up";
130 }
131
getAnalysisUsage__anonfdaa28eb0111::LDTLSCleanup132 void getAnalysisUsage(AnalysisUsage &AU) const override {
133 AU.setPreservesCFG();
134 AU.addRequired<MachineDominatorTree>();
135 MachineFunctionPass::getAnalysisUsage(AU);
136 }
137 };
138 }
139
140 char LDTLSCleanup::ID = 0;
createAArch64CleanupLocalDynamicTLSPass()141 FunctionPass *llvm::createAArch64CleanupLocalDynamicTLSPass() {
142 return new LDTLSCleanup();
143 }
144