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 TII = static_cast<const SystemZInstrInfo *>(F.getSubtarget().getInstrInfo());
68 MF = &F;
69
70 SystemZMachineFunctionInfo* MFI = F.getInfo<SystemZMachineFunctionInfo>();
71 if (MFI->getNumLocalDynamicTLSAccesses() < 2) {
72 // No point folding accesses if there isn't at least two.
73 return false;
74 }
75
76 MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
77 return VisitNode(DT->getRootNode(), 0);
78 }
79
80 // Visit the dominator subtree rooted at Node in pre-order.
81 // If TLSBaseAddrReg is non-null, then use that to replace any
82 // TLS_LDCALL instructions. Otherwise, create the register
83 // when the first such instruction is seen, and then use it
84 // as we encounter more instructions.
VisitNode(MachineDomTreeNode * Node,unsigned TLSBaseAddrReg)85 bool SystemZLDCleanup::VisitNode(MachineDomTreeNode *Node,
86 unsigned TLSBaseAddrReg) {
87 MachineBasicBlock *BB = Node->getBlock();
88 bool Changed = false;
89
90 // Traverse the current block.
91 for (auto I = BB->begin(), E = BB->end(); I != E; ++I) {
92 switch (I->getOpcode()) {
93 case SystemZ::TLS_LDCALL:
94 if (TLSBaseAddrReg)
95 I = ReplaceTLSCall(I, TLSBaseAddrReg);
96 else
97 I = SetRegister(I, &TLSBaseAddrReg);
98 Changed = true;
99 break;
100 default:
101 break;
102 }
103 }
104
105 // Visit the children of this block in the dominator tree.
106 for (auto I = Node->begin(), E = Node->end(); I != E; ++I)
107 Changed |= VisitNode(*I, TLSBaseAddrReg);
108
109 return Changed;
110 }
111
112 // Replace the TLS_LDCALL instruction I with a copy from TLSBaseAddrReg,
113 // returning the new instruction.
ReplaceTLSCall(MachineInstr * I,unsigned TLSBaseAddrReg)114 MachineInstr *SystemZLDCleanup::ReplaceTLSCall(MachineInstr *I,
115 unsigned TLSBaseAddrReg) {
116 // Insert a Copy from TLSBaseAddrReg to R2.
117 MachineInstr *Copy = BuildMI(*I->getParent(), I, I->getDebugLoc(),
118 TII->get(TargetOpcode::COPY), SystemZ::R2D)
119 .addReg(TLSBaseAddrReg);
120
121 // Erase the TLS_LDCALL instruction.
122 I->eraseFromParent();
123
124 return Copy;
125 }
126
127 // Create a virtal register in *TLSBaseAddrReg, and populate it by
128 // inserting a copy instruction after I. Returns the new instruction.
SetRegister(MachineInstr * I,unsigned * TLSBaseAddrReg)129 MachineInstr *SystemZLDCleanup::SetRegister(MachineInstr *I,
130 unsigned *TLSBaseAddrReg) {
131 // Create a virtual register for the TLS base address.
132 MachineRegisterInfo &RegInfo = MF->getRegInfo();
133 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&SystemZ::GR64BitRegClass);
134
135 // Insert a copy from R2 to TLSBaseAddrReg.
136 MachineInstr *Next = I->getNextNode();
137 MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(),
138 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
139 .addReg(SystemZ::R2D);
140
141 return Copy;
142 }
143
144