lib/Target/SystemZ/SystemZLDCleanup.cpp

   1 //===-- SystemZLDCleanup.cpp - Clean up local-dynamic TLS accesses --------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This pass combines multiple accesses to local-dynamic TLS variables so that
  11 // the TLS base address for the module is only fetched once per execution path
  12 // through the function.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "SystemZMachineFunctionInfo.h"
  17 #include "SystemZTargetMachine.h"
  18 #include "llvm/CodeGen/MachineDominators.h"
  19 #include "llvm/CodeGen/MachineFunctionPass.h"
  20 #include "llvm/CodeGen/MachineInstrBuilder.h"
  21 #include "llvm/CodeGen/MachineRegisterInfo.h"
  22 #include "llvm/CodeGen/TargetInstrInfo.h"
  23 #include "llvm/CodeGen/TargetRegisterInfo.h"
  24 #include "llvm/Target/TargetMachine.h"
  25
  26 using namespace llvm;
  27
  28 namespace {
  29
  30 class SystemZLDCleanup : public MachineFunctionPass {
  31 public:
  32   static char ID;
  33   SystemZLDCleanup(const SystemZTargetMachine &tm)
  34     : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {}
  35
  36   StringRef getPassName() const override {
  37     return "SystemZ Local Dynamic TLS Access Clean-up";
  38   }
  39
  40   bool runOnMachineFunction(MachineFunction &MF) override;
  41   void getAnalysisUsage(AnalysisUsage &AU) const override;
  42
  43 private:
  44   bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg);
  45   MachineInstr *ReplaceTLSCall(MachineInstr *I, unsigned TLSBaseAddrReg);
  46   MachineInstr *SetRegister(MachineInstr *I, unsigned *TLSBaseAddrReg);
  47
  48   const SystemZInstrInfo *TII;
  49   MachineFunction *MF;
  50 };
  51
  52 char SystemZLDCleanup::ID = 0;
  53
  54 } // end anonymous namespace
  55
  56 FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
  57   return new SystemZLDCleanup(TM);
  58 }
  59
  60 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
  61   AU.setPreservesCFG();
  62   AU.addRequired<MachineDominatorTree>();
  63   MachineFunctionPass::getAnalysisUsage(AU);
  64 }
  65
  66 bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) {
  67   if (skipFunction(F.getFunction()))
  68     return false;
  69
  70   TII = static_cast<const SystemZInstrInfo *>(F.getSubtarget().getInstrInfo());
  71   MF = &F;
  72
  73   SystemZMachineFunctionInfo* MFI = F.getInfo<SystemZMachineFunctionInfo>();
  74   if (MFI->getNumLocalDynamicTLSAccesses() < 2) {
  75     // No point folding accesses if there isn't at least two.
  76     return false;
  77   }
  78
  79   MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
  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 I = Node->begin(), E = Node->end(); I != E; ++I)
 110     Changed |= VisitNode(*I, 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