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 "SystemZTargetMachine.h"
17 #include "SystemZMachineFunctionInfo.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/Target/TargetInstrInfo.h"
23 #include "llvm/Target/TargetMachine.h"
24 #include "llvm/Target/TargetRegisterInfo.h"
25
26 using namespace llvm;
27
28 namespace {
29
30 class SystemZLDCleanup : public MachineFunctionPass {
31 public:
32 static char ID;
SystemZLDCleanup(const SystemZTargetMachine & tm)33 SystemZLDCleanup(const SystemZTargetMachine &tm)
34 : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {}
35
getPassName() const36 const char *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
createSystemZLDCleanupPass(SystemZTargetMachine & TM)56 FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
57 return new SystemZLDCleanup(TM);
58 }
59
getAnalysisUsage(AnalysisUsage & AU) const60 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
61 AU.setPreservesCFG();
62 AU.addRequired<MachineDominatorTree>();
63 MachineFunctionPass::getAnalysisUsage(AU);
64 }
65
runOnMachineFunction(MachineFunction & F)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.
VisitNode(MachineDomTreeNode * Node,unsigned TLSBaseAddrReg)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.
ReplaceTLSCall(MachineInstr * I,unsigned TLSBaseAddrReg)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 virtal register in *TLSBaseAddrReg, and populate it by
131 // inserting a copy instruction after I. Returns the new instruction.
SetRegister(MachineInstr * I,unsigned * TLSBaseAddrReg)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
147