lib/Target/SystemZ/SystemZLDCleanup.cpp

   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(const SystemZTargetMachine &tm)
  33     : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {}
  34
  35   StringRef getPassName() const override {
  36     return "SystemZ Local Dynamic TLS Access Clean-up";
  37   }
  38
  39   bool runOnMachineFunction(MachineFunction &MF) override;
  40   void getAnalysisUsage(AnalysisUsage &AU) const override;
  41
  42 private:
  43   bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg);
  44   MachineInstr *ReplaceTLSCall(MachineInstr *I, unsigned TLSBaseAddrReg);
  45   MachineInstr *SetRegister(MachineInstr *I, unsigned *TLSBaseAddrReg);
  46
  47   const SystemZInstrInfo *TII;
  48   MachineFunction *MF;
  49 };
  50
  51 char SystemZLDCleanup::ID = 0;
  52
  53 } // end anonymous namespace
  54
  55 FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
  56   return new SystemZLDCleanup(TM);
  57 }
  58
  59 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
  60   AU.setPreservesCFG();
  61   AU.addRequired<MachineDominatorTree>();
  62   MachineFunctionPass::getAnalysisUsage(AU);
  63 }
  64
  65 bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) {
  66   if (skipFunction(F.getFunction()))
  67     return false;
  68
  69   TII = static_cast<const SystemZInstrInfo *>(F.getSubtarget().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 = &getAnalysis<MachineDominatorTree>();
  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 I = Node->begin(), E = Node->end(); I != E; ++I)
 109     Changed |= VisitNode(*I, 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