SystemZLDCleanup.cpp revision 355940 
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
25using namespace llvm;
26
27namespace {
28
29class SystemZLDCleanup : public MachineFunctionPass {
30public:
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
42private:
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
51char SystemZLDCleanup::ID = 0;
52
53} // end anonymous namespace
54
55FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
56  return new SystemZLDCleanup(TM);
57}
58
59void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
60  AU.setPreservesCFG();
61  AU.addRequired<MachineDominatorTree>();
62  MachineFunctionPass::getAnalysisUsage(AU);
63}
64
65bool 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.
87bool 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.
116MachineInstr *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.
131MachineInstr *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