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;
SystemZLDCleanup(const SystemZTargetMachine & tm)32 SystemZLDCleanup(const SystemZTargetMachine &tm)
33 : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {}
34
getPassName() const35 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
createSystemZLDCleanupPass(SystemZTargetMachine & TM)55 FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
56 return new SystemZLDCleanup(TM);
57 }
58
getAnalysisUsage(AnalysisUsage & AU) const59 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
60 AU.setPreservesCFG();
61 AU.addRequired<MachineDominatorTree>();
62 MachineFunctionPass::getAnalysisUsage(AU);
63 }
64
runOnMachineFunction(MachineFunction & F)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.
VisitNode(MachineDomTreeNode * Node,unsigned TLSBaseAddrReg)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.
ReplaceTLSCall(MachineInstr * I,unsigned TLSBaseAddrReg)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.
SetRegister(MachineInstr * I,unsigned * TLSBaseAddrReg)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