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 #include "llvm/Target/TargetMachine.h" 24 25 using namespace llvm; 26 27 namespace { 28 29 class SystemZLDCleanup : public MachineFunctionPass { 30 public: 31 static char ID; 32 SystemZLDCleanup() : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) { 33 initializeSystemZLDCleanupPass(*PassRegistry::getPassRegistry()); 34 } 35 36 bool runOnMachineFunction(MachineFunction &MF) override; 37 void getAnalysisUsage(AnalysisUsage &AU) const override; 38 39 private: 40 bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg); 41 MachineInstr *ReplaceTLSCall(MachineInstr *I, unsigned TLSBaseAddrReg); 42 MachineInstr *SetRegister(MachineInstr *I, unsigned *TLSBaseAddrReg); 43 44 const SystemZInstrInfo *TII; 45 MachineFunction *MF; 46 }; 47 48 char SystemZLDCleanup::ID = 0; 49 50 } // end anonymous namespace 51 52 INITIALIZE_PASS(SystemZLDCleanup, "systemz-ld-cleanup", 53 "SystemZ Local Dynamic TLS Access Clean-up", false, false) 54 55 FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) { 56 return new SystemZLDCleanup(); 57 } 58 59 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const { 60 AU.setPreservesCFG(); 61 AU.addRequired<MachineDominatorTreeWrapperPass>(); 62 MachineFunctionPass::getAnalysisUsage(AU); 63 } 64 65 bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) { 66 if (skipFunction(F.getFunction())) 67 return false; 68 69 TII = F.getSubtarget<SystemZSubtarget>().getInstrInfo(); 70 MF = &F; 71 72 SystemZMachineFunctionInfo* MFI = F.getInfo<SystemZMachineFunctionInfo>(); 73 if (MFI->getNumLocalDynamicTLSAccesses() < 2) { 74 // No point folding accesses if there isn't at least two. 75 return false; 76 } 77 78 MachineDominatorTree *DT = 79 &getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree(); 80 return VisitNode(DT->getRootNode(), 0); 81 } 82 83 // Visit the dominator subtree rooted at Node in pre-order. 84 // If TLSBaseAddrReg is non-null, then use that to replace any 85 // TLS_LDCALL instructions. Otherwise, create the register 86 // when the first such instruction is seen, and then use it 87 // as we encounter more instructions. 88 bool SystemZLDCleanup::VisitNode(MachineDomTreeNode *Node, 89 unsigned TLSBaseAddrReg) { 90 MachineBasicBlock *BB = Node->getBlock(); 91 bool Changed = false; 92 93 // Traverse the current block. 94 for (auto I = BB->begin(), E = BB->end(); I != E; ++I) { 95 switch (I->getOpcode()) { 96 case SystemZ::TLS_LDCALL: 97 if (TLSBaseAddrReg) 98 I = ReplaceTLSCall(&*I, TLSBaseAddrReg); 99 else 100 I = SetRegister(&*I, &TLSBaseAddrReg); 101 Changed = true; 102 break; 103 default: 104 break; 105 } 106 } 107 108 // Visit the children of this block in the dominator tree. 109 for (auto &N : *Node) 110 Changed |= VisitNode(N, TLSBaseAddrReg); 111 112 return Changed; 113 } 114 115 // Replace the TLS_LDCALL instruction I with a copy from TLSBaseAddrReg, 116 // returning the new instruction. 117 MachineInstr *SystemZLDCleanup::ReplaceTLSCall(MachineInstr *I, 118 unsigned TLSBaseAddrReg) { 119 // Insert a Copy from TLSBaseAddrReg to R2. 120 MachineInstr *Copy = BuildMI(*I->getParent(), I, I->getDebugLoc(), 121 TII->get(TargetOpcode::COPY), SystemZ::R2D) 122 .addReg(TLSBaseAddrReg); 123 124 // Erase the TLS_LDCALL instruction. 125 I->eraseFromParent(); 126 127 return Copy; 128 } 129 130 // Create a virtual register in *TLSBaseAddrReg, and populate it by 131 // inserting a copy instruction after I. Returns the new instruction. 132 MachineInstr *SystemZLDCleanup::SetRegister(MachineInstr *I, 133 unsigned *TLSBaseAddrReg) { 134 // Create a virtual register for the TLS base address. 135 MachineRegisterInfo &RegInfo = MF->getRegInfo(); 136 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&SystemZ::GR64BitRegClass); 137 138 // Insert a copy from R2 to TLSBaseAddrReg. 139 MachineInstr *Next = I->getNextNode(); 140 MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(), 141 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg) 142 .addReg(SystemZ::R2D); 143 144 return Copy; 145 } 146 147