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 "AArch64InstrInfo.h"
26 #include "AArch64MachineFunctionInfo.h"
27 #include "llvm/CodeGen/MachineDominators.h"
28 #include "llvm/CodeGen/MachineFunction.h"
29 #include "llvm/CodeGen/MachineFunctionPass.h"
30 #include "llvm/CodeGen/MachineInstrBuilder.h"
31 #include "llvm/CodeGen/MachineRegisterInfo.h"
32 using namespace llvm;
33
34 #define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
35
36 namespace {
37 struct LDTLSCleanup : public MachineFunctionPass {
38 static char ID;
LDTLSCleanup__anon99a195310111::LDTLSCleanup39 LDTLSCleanup() : MachineFunctionPass(ID) {
40 initializeLDTLSCleanupPass(*PassRegistry::getPassRegistry());
41 }
42
runOnMachineFunction__anon99a195310111::LDTLSCleanup43 bool runOnMachineFunction(MachineFunction &MF) override {
44 if (skipFunction(MF.getFunction()))
45 return false;
46
47 AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
48 if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
49 // No point folding accesses if there isn't at least two.
50 return false;
51 }
52
53 MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
54 return VisitNode(DT->getRootNode(), 0);
55 }
56
57 // Visit the dominator subtree rooted at Node in pre-order.
58 // If TLSBaseAddrReg is non-null, then use that to replace any
59 // TLS_base_addr instructions. Otherwise, create the register
60 // when the first such instruction is seen, and then use it
61 // as we encounter more instructions.
VisitNode__anon99a195310111::LDTLSCleanup62 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
63 MachineBasicBlock *BB = Node->getBlock();
64 bool Changed = false;
65
66 // Traverse the current block.
67 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
68 ++I) {
69 switch (I->getOpcode()) {
70 case AArch64::TLSDESC_CALLSEQ:
71 // Make sure it's a local dynamic access.
72 if (!I->getOperand(0).isSymbol() ||
73 strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
74 break;
75
76 if (TLSBaseAddrReg)
77 I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
78 else
79 I = setRegister(*I, &TLSBaseAddrReg);
80 Changed = true;
81 break;
82 default:
83 break;
84 }
85 }
86
87 // Visit the children of this block in the dominator tree.
88 for (MachineDomTreeNode *N : *Node) {
89 Changed |= VisitNode(N, TLSBaseAddrReg);
90 }
91
92 return Changed;
93 }
94
95 // Replace the TLS_base_addr instruction I with a copy from
96 // TLSBaseAddrReg, returning the new instruction.
replaceTLSBaseAddrCall__anon99a195310111::LDTLSCleanup97 MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
98 unsigned TLSBaseAddrReg) {
99 MachineFunction *MF = I.getParent()->getParent();
100 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
101
102 // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
103 // code sequence assumes the address will be.
104 MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
105 TII->get(TargetOpcode::COPY), AArch64::X0)
106 .addReg(TLSBaseAddrReg);
107
108 // Update the call site info.
109 if (I.shouldUpdateCallSiteInfo())
110 I.getMF()->eraseCallSiteInfo(&I);
111
112 // Erase the TLS_base_addr instruction.
113 I.eraseFromParent();
114
115 return Copy;
116 }
117
118 // Create a virtual register in *TLSBaseAddrReg, and populate it by
119 // inserting a copy instruction after I. Returns the new instruction.
setRegister__anon99a195310111::LDTLSCleanup120 MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
121 MachineFunction *MF = I.getParent()->getParent();
122 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
123
124 // Create a virtual register for the TLS base address.
125 MachineRegisterInfo &RegInfo = MF->getRegInfo();
126 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
127
128 // Insert a copy from X0 to TLSBaseAddrReg for later.
129 MachineInstr *Copy =
130 BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
131 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
132 .addReg(AArch64::X0);
133
134 return Copy;
135 }
136
getPassName__anon99a195310111::LDTLSCleanup137 StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
138
getAnalysisUsage__anon99a195310111::LDTLSCleanup139 void getAnalysisUsage(AnalysisUsage &AU) const override {
140 AU.setPreservesCFG();
141 AU.addRequired<MachineDominatorTree>();
142 MachineFunctionPass::getAnalysisUsage(AU);
143 }
144 };
145 }
146
147 INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
148 TLSCLEANUP_PASS_NAME, false, false)
149
150 char LDTLSCleanup::ID = 0;
createAArch64CleanupLocalDynamicTLSPass()151 FunctionPass *llvm::createAArch64CleanupLocalDynamicTLSPass() {
152 return new LDTLSCleanup();
153 }
154