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__anonc72a33300111::LDTLSCleanup39 LDTLSCleanup() : MachineFunctionPass(ID) {}
40
runOnMachineFunction__anonc72a33300111::LDTLSCleanup41 bool runOnMachineFunction(MachineFunction &MF) override {
42 if (skipFunction(*MF.getFunction()))
43 return false;
44
45 AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
46 if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
47 // No point folding accesses if there isn't at least two.
48 return false;
49 }
50
51 MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
52 return VisitNode(DT->getRootNode(), 0);
53 }
54
55 // Visit the dominator subtree rooted at Node in pre-order.
56 // If TLSBaseAddrReg is non-null, then use that to replace any
57 // TLS_base_addr instructions. Otherwise, create the register
58 // when the first such instruction is seen, and then use it
59 // as we encounter more instructions.
VisitNode__anonc72a33300111::LDTLSCleanup60 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
61 MachineBasicBlock *BB = Node->getBlock();
62 bool Changed = false;
63
64 // Traverse the current block.
65 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
66 ++I) {
67 switch (I->getOpcode()) {
68 case AArch64::TLSDESC_CALLSEQ:
69 // Make sure it's a local dynamic access.
70 if (!I->getOperand(0).isSymbol() ||
71 strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
72 break;
73
74 if (TLSBaseAddrReg)
75 I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
76 else
77 I = setRegister(*I, &TLSBaseAddrReg);
78 Changed = true;
79 break;
80 default:
81 break;
82 }
83 }
84
85 // Visit the children of this block in the dominator tree.
86 for (MachineDomTreeNode *N : *Node) {
87 Changed |= VisitNode(N, TLSBaseAddrReg);
88 }
89
90 return Changed;
91 }
92
93 // Replace the TLS_base_addr instruction I with a copy from
94 // TLSBaseAddrReg, returning the new instruction.
replaceTLSBaseAddrCall__anonc72a33300111::LDTLSCleanup95 MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
96 unsigned TLSBaseAddrReg) {
97 MachineFunction *MF = I.getParent()->getParent();
98 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
99
100 // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
101 // code sequence assumes the address will be.
102 MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
103 TII->get(TargetOpcode::COPY), AArch64::X0)
104 .addReg(TLSBaseAddrReg);
105
106 // Erase the TLS_base_addr instruction.
107 I.eraseFromParent();
108
109 return Copy;
110 }
111
112 // Create a virtal register in *TLSBaseAddrReg, and populate it by
113 // inserting a copy instruction after I. Returns the new instruction.
setRegister__anonc72a33300111::LDTLSCleanup114 MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
115 MachineFunction *MF = I.getParent()->getParent();
116 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
117
118 // Create a virtual register for the TLS base address.
119 MachineRegisterInfo &RegInfo = MF->getRegInfo();
120 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
121
122 // Insert a copy from X0 to TLSBaseAddrReg for later.
123 MachineInstr *Copy =
124 BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
125 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
126 .addReg(AArch64::X0);
127
128 return Copy;
129 }
130
getPassName__anonc72a33300111::LDTLSCleanup131 const char *getPassName() const override {
132 return "Local Dynamic TLS Access Clean-up";
133 }
134
getAnalysisUsage__anonc72a33300111::LDTLSCleanup135 void getAnalysisUsage(AnalysisUsage &AU) const override {
136 AU.setPreservesCFG();
137 AU.addRequired<MachineDominatorTree>();
138 MachineFunctionPass::getAnalysisUsage(AU);
139 }
140 };
141 }
142
143 char LDTLSCleanup::ID = 0;
createAArch64CleanupLocalDynamicTLSPass()144 FunctionPass *llvm::createAArch64CleanupLocalDynamicTLSPass() {
145 return new LDTLSCleanup();
146 }
147