1 //===-- AArch64CleanupLocalDynamicTLSPass.cpp ---------------------*- C++ -*-=//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Local-dynamic access to thread-local variables proceeds in three stages.
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
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.
24 //===----------------------------------------------------------------------===//
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"
36 #define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
39 struct LDTLSCleanup : public MachineFunctionPass {
41 LDTLSCleanup() : MachineFunctionPass(ID) {
42 initializeLDTLSCleanupPass(*PassRegistry::getPassRegistry());
45 bool runOnMachineFunction(MachineFunction &MF) override {
46 if (skipFunction(*MF.getFunction()))
49 AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
50 if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
51 // No point folding accesses if there isn't at least two.
55 MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
56 return VisitNode(DT->getRootNode(), 0);
59 // Visit the dominator subtree rooted at Node in pre-order.
60 // If TLSBaseAddrReg is non-null, then use that to replace any
61 // TLS_base_addr instructions. Otherwise, create the register
62 // when the first such instruction is seen, and then use it
63 // as we encounter more instructions.
64 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
65 MachineBasicBlock *BB = Node->getBlock();
68 // Traverse the current block.
69 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
71 switch (I->getOpcode()) {
72 case AArch64::TLSDESC_CALLSEQ:
73 // Make sure it's a local dynamic access.
74 if (!I->getOperand(0).isSymbol() ||
75 strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
79 I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
81 I = setRegister(*I, &TLSBaseAddrReg);
89 // Visit the children of this block in the dominator tree.
90 for (MachineDomTreeNode *N : *Node) {
91 Changed |= VisitNode(N, TLSBaseAddrReg);
97 // Replace the TLS_base_addr instruction I with a copy from
98 // TLSBaseAddrReg, returning the new instruction.
99 MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
100 unsigned TLSBaseAddrReg) {
101 MachineFunction *MF = I.getParent()->getParent();
102 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
104 // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
105 // code sequence assumes the address will be.
106 MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
107 TII->get(TargetOpcode::COPY), AArch64::X0)
108 .addReg(TLSBaseAddrReg);
110 // Erase the TLS_base_addr instruction.
116 // Create a virtal register in *TLSBaseAddrReg, and populate it by
117 // inserting a copy instruction after I. Returns the new instruction.
118 MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
119 MachineFunction *MF = I.getParent()->getParent();
120 const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
122 // Create a virtual register for the TLS base address.
123 MachineRegisterInfo &RegInfo = MF->getRegInfo();
124 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
126 // Insert a copy from X0 to TLSBaseAddrReg for later.
128 BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
129 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
130 .addReg(AArch64::X0);
135 StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
137 void getAnalysisUsage(AnalysisUsage &AU) const override {
138 AU.setPreservesCFG();
139 AU.addRequired<MachineDominatorTree>();
140 MachineFunctionPass::getAnalysisUsage(AU);
145 INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
146 TLSCLEANUP_PASS_NAME, false, false)
148 char LDTLSCleanup::ID = 0;
149 FunctionPass *llvm::createAArch64CleanupLocalDynamicTLSPass() {
150 return new LDTLSCleanup();