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