1 //===-- AArch64CleanupLocalDynamicTLSPass.cpp ---------------------*- C++ -*-=//
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 // Local-dynamic access to thread-local variables proceeds in three stages.
10 //
11 // 1. The offset of this Module's thread-local area from TPIDR_EL0 is calculated
12 // in much the same way as a general-dynamic TLS-descriptor access against
13 // the special symbol _TLS_MODULE_BASE.
14 // 2. The variable's offset from _TLS_MODULE_BASE_ is calculated using
15 // instructions with "dtprel" modifiers.
16 // 3. These two are added, together with TPIDR_EL0, to obtain the variable's
17 // true address.
18 //
19 // This is only better than general-dynamic access to the variable if two or
20 // more of the first stage TLS-descriptor calculations can be combined. This
21 // pass looks through a function and performs such combinations.
22 //
23 //===----------------------------------------------------------------------===//
24 #include "AArch64.h"
25 #include "AArch64MachineFunctionInfo.h"
26 #include "llvm/CodeGen/MachineDominators.h"
27 #include "llvm/CodeGen/MachineFunction.h"
28 #include "llvm/CodeGen/MachineFunctionPass.h"
29 #include "llvm/CodeGen/MachineInstrBuilder.h"
30 #include "llvm/CodeGen/MachineRegisterInfo.h"
31 using namespace llvm;
32
33 #define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
34
35 namespace {
36 struct LDTLSCleanup : public MachineFunctionPass {
37 static char ID;
LDTLSCleanup__anon2c1b92090111::LDTLSCleanup38 LDTLSCleanup() : MachineFunctionPass(ID) {}
39
runOnMachineFunction__anon2c1b92090111::LDTLSCleanup40 bool runOnMachineFunction(MachineFunction &MF) override {
41 if (skipFunction(MF.getFunction()))
42 return false;
43
44 AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
45 if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
46 // No point folding accesses if there isn't at least two.
47 return false;
48 }
49
50 MachineDominatorTree *DT =
51 &getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree();
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__anon2c1b92090111::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__anon2c1b92090111::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 // Update the call info.
107 if (I.shouldUpdateAdditionalCallInfo())
108 I.getMF()->eraseAdditionalCallInfo(&I);
109
110 // Erase the TLS_base_addr instruction.
111 I.eraseFromParent();
112
113 return Copy;
114 }
115
116 // Create a virtual register in *TLSBaseAddrReg, and populate it by
117 // inserting a copy instruction after I. Returns the new instruction.
setRegister__anon2c1b92090111::LDTLSCleanup118 MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
119 MachineFunction *MF = I.getParent()->getParent();
120 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
121
122 // Create a virtual register for the TLS base address.
123 MachineRegisterInfo &RegInfo = MF->getRegInfo();
124 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
125
126 // Insert a copy from X0 to TLSBaseAddrReg for later.
127 MachineInstr *Copy =
128 BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
129 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
130 .addReg(AArch64::X0);
131
132 return Copy;
133 }
134
getPassName__anon2c1b92090111::LDTLSCleanup135 StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
136
getAnalysisUsage__anon2c1b92090111::LDTLSCleanup137 void getAnalysisUsage(AnalysisUsage &AU) const override {
138 AU.setPreservesCFG();
139 AU.addRequired<MachineDominatorTreeWrapperPass>();
140 MachineFunctionPass::getAnalysisUsage(AU);
141 }
142 };
143 }
144
145 INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
146 TLSCLEANUP_PASS_NAME, false, false)
147
148 char LDTLSCleanup::ID = 0;
createAArch64CleanupLocalDynamicTLSPass()149 FunctionPass *llvm::createAArch64CleanupLocalDynamicTLSPass() {
150 return new LDTLSCleanup();
151 }
152