1 //===-- ARM64CleanupLocalDynamicTLSPass.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 "ARM64InstrInfo.h"
27 #include "ARM64MachineFunctionInfo.h"
28 #include "ARM64TargetMachine.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"
37 struct LDTLSCleanup : public MachineFunctionPass {
39 LDTLSCleanup() : MachineFunctionPass(ID) {}
41 virtual bool runOnMachineFunction(MachineFunction &MF) {
42 ARM64FunctionInfo *AFI = MF.getInfo<ARM64FunctionInfo>();
43 if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
44 // No point folding accesses if there isn't at least two.
48 MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
49 return VisitNode(DT->getRootNode(), 0);
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.
57 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
58 MachineBasicBlock *BB = Node->getBlock();
61 // Traverse the current block.
62 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
64 switch (I->getOpcode()) {
65 case ARM64::TLSDESC_BLR:
66 // Make sure it's a local dynamic access.
67 if (!I->getOperand(1).isSymbol() ||
68 strcmp(I->getOperand(1).getSymbolName(), "_TLS_MODULE_BASE_"))
72 I = replaceTLSBaseAddrCall(I, TLSBaseAddrReg);
74 I = setRegister(I, &TLSBaseAddrReg);
82 // Visit the children of this block in the dominator tree.
83 for (MachineDomTreeNode *N : *Node) {
84 Changed |= VisitNode(N, TLSBaseAddrReg);
90 // Replace the TLS_base_addr instruction I with a copy from
91 // TLSBaseAddrReg, returning the new instruction.
92 MachineInstr *replaceTLSBaseAddrCall(MachineInstr *I,
93 unsigned TLSBaseAddrReg) {
94 MachineFunction *MF = I->getParent()->getParent();
95 const ARM64TargetMachine *TM =
96 static_cast<const ARM64TargetMachine *>(&MF->getTarget());
97 const ARM64InstrInfo *TII = TM->getInstrInfo();
99 // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
100 // code sequence assumes the address will be.
102 BuildMI(*I->getParent(), I, I->getDebugLoc(),
103 TII->get(TargetOpcode::COPY), ARM64::X0).addReg(TLSBaseAddrReg);
105 // Erase the TLS_base_addr instruction.
106 I->eraseFromParent();
111 // Create a virtal register in *TLSBaseAddrReg, and populate it by
112 // inserting a copy instruction after I. Returns the new instruction.
113 MachineInstr *setRegister(MachineInstr *I, unsigned *TLSBaseAddrReg) {
114 MachineFunction *MF = I->getParent()->getParent();
115 const ARM64TargetMachine *TM =
116 static_cast<const ARM64TargetMachine *>(&MF->getTarget());
117 const ARM64InstrInfo *TII = TM->getInstrInfo();
119 // Create a virtual register for the TLS base address.
120 MachineRegisterInfo &RegInfo = MF->getRegInfo();
121 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&ARM64::GPR64RegClass);
123 // Insert a copy from X0 to TLSBaseAddrReg for later.
124 MachineInstr *Next = I->getNextNode();
125 MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(),
126 TII->get(TargetOpcode::COPY),
127 *TLSBaseAddrReg).addReg(ARM64::X0);
132 virtual const char *getPassName() const {
133 return "Local Dynamic TLS Access Clean-up";
136 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
137 AU.setPreservesCFG();
138 AU.addRequired<MachineDominatorTree>();
139 MachineFunctionPass::getAnalysisUsage(AU);
144 char LDTLSCleanup::ID = 0;
145 FunctionPass *llvm::createARM64CleanupLocalDynamicTLSPass() {
146 return new LDTLSCleanup();