1 //===-- SystemZLDCleanup.cpp - Clean up local-dynamic TLS accesses --------===// 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 // This pass combines multiple accesses to local-dynamic TLS variables so that 10 // the TLS base address for the module is only fetched once per execution path 11 // through the function. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "SystemZMachineFunctionInfo.h" 16 #include "SystemZTargetMachine.h" 17 #include "llvm/CodeGen/MachineDominators.h" 18 #include "llvm/CodeGen/MachineFunctionPass.h" 19 #include "llvm/CodeGen/MachineInstrBuilder.h" 20 #include "llvm/CodeGen/MachineRegisterInfo.h" 21 #include "llvm/CodeGen/TargetInstrInfo.h" 22 #include "llvm/CodeGen/TargetRegisterInfo.h" 23 24 using namespace llvm; 25 26 namespace { 27 28 class SystemZLDCleanup : public MachineFunctionPass { 29 public: 30 static char ID; 31 SystemZLDCleanup() : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {} 32 33 bool runOnMachineFunction(MachineFunction &MF) override; 34 void getAnalysisUsage(AnalysisUsage &AU) const override; 35 36 private: 37 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg); 38 MachineInstr *ReplaceTLSCall(MachineInstr *I, unsigned TLSBaseAddrReg); 39 MachineInstr *SetRegister(MachineInstr *I, unsigned *TLSBaseAddrReg); 40 41 const SystemZInstrInfo *TII; 42 MachineFunction *MF; 43 }; 44 45 char SystemZLDCleanup::ID = 0; 46 47 } // end anonymous namespace 48 49 INITIALIZE_PASS(SystemZLDCleanup, "systemz-ld-cleanup", 50 "SystemZ Local Dynamic TLS Access Clean-up", false, false) 51 52 FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) { 53 return new SystemZLDCleanup(); 54 } 55 56 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const { 57 AU.setPreservesCFG(); 58 AU.addRequired<MachineDominatorTreeWrapperPass>(); 59 MachineFunctionPass::getAnalysisUsage(AU); 60 } 61 62 bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) { 63 if (skipFunction(F.getFunction())) 64 return false; 65 66 TII = F.getSubtarget<SystemZSubtarget>().getInstrInfo(); 67 MF = &F; 68 69 SystemZMachineFunctionInfo* MFI = F.getInfo<SystemZMachineFunctionInfo>(); 70 if (MFI->getNumLocalDynamicTLSAccesses() < 2) { 71 // No point folding accesses if there isn't at least two. 72 return false; 73 } 74 75 MachineDominatorTree *DT = 76 &getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree(); 77 return VisitNode(DT->getRootNode(), 0); 78 } 79 80 // Visit the dominator subtree rooted at Node in pre-order. 81 // If TLSBaseAddrReg is non-null, then use that to replace any 82 // TLS_LDCALL instructions. Otherwise, create the register 83 // when the first such instruction is seen, and then use it 84 // as we encounter more instructions. 85 bool SystemZLDCleanup::VisitNode(MachineDomTreeNode *Node, 86 unsigned TLSBaseAddrReg) { 87 MachineBasicBlock *BB = Node->getBlock(); 88 bool Changed = false; 89 90 // Traverse the current block. 91 for (auto I = BB->begin(), E = BB->end(); I != E; ++I) { 92 switch (I->getOpcode()) { 93 case SystemZ::TLS_LDCALL: 94 if (TLSBaseAddrReg) 95 I = ReplaceTLSCall(&*I, TLSBaseAddrReg); 96 else 97 I = SetRegister(&*I, &TLSBaseAddrReg); 98 Changed = true; 99 break; 100 default: 101 break; 102 } 103 } 104 105 // Visit the children of this block in the dominator tree. 106 for (auto &N : *Node) 107 Changed |= VisitNode(N, TLSBaseAddrReg); 108 109 return Changed; 110 } 111 112 // Replace the TLS_LDCALL instruction I with a copy from TLSBaseAddrReg, 113 // returning the new instruction. 114 MachineInstr *SystemZLDCleanup::ReplaceTLSCall(MachineInstr *I, 115 unsigned TLSBaseAddrReg) { 116 // Insert a Copy from TLSBaseAddrReg to R2. 117 MachineInstr *Copy = BuildMI(*I->getParent(), I, I->getDebugLoc(), 118 TII->get(TargetOpcode::COPY), SystemZ::R2D) 119 .addReg(TLSBaseAddrReg); 120 121 // Erase the TLS_LDCALL instruction. 122 I->eraseFromParent(); 123 124 return Copy; 125 } 126 127 // Create a virtual register in *TLSBaseAddrReg, and populate it by 128 // inserting a copy instruction after I. Returns the new instruction. 129 MachineInstr *SystemZLDCleanup::SetRegister(MachineInstr *I, 130 unsigned *TLSBaseAddrReg) { 131 // Create a virtual register for the TLS base address. 132 MachineRegisterInfo &RegInfo = MF->getRegInfo(); 133 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&SystemZ::GR64BitRegClass); 134 135 // Insert a copy from R2 to TLSBaseAddrReg. 136 MachineInstr *Next = I->getNextNode(); 137 MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(), 138 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg) 139 .addReg(SystemZ::R2D); 140 141 return Copy; 142 } 143 144