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;
32   SystemZLDCleanup() : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {
33     initializeSystemZLDCleanupPass(*PassRegistry::getPassRegistry());
34   }
35 
36   bool runOnMachineFunction(MachineFunction &MF) override;
37   void getAnalysisUsage(AnalysisUsage &AU) const override;
38 
39 private:
40   bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg);
41   MachineInstr *ReplaceTLSCall(MachineInstr *I, unsigned TLSBaseAddrReg);
42   MachineInstr *SetRegister(MachineInstr *I, unsigned *TLSBaseAddrReg);
43 
44   const SystemZInstrInfo *TII;
45   MachineFunction *MF;
46 };
47 
48 char SystemZLDCleanup::ID = 0;
49 
50 } // end anonymous namespace
51 
52 INITIALIZE_PASS(SystemZLDCleanup, "systemz-ld-cleanup",
53                 "SystemZ Local Dynamic TLS Access Clean-up", false, false)
54 
55 FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
56   return new SystemZLDCleanup();
57 }
58 
59 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
60   AU.setPreservesCFG();
61   AU.addRequired<MachineDominatorTree>();
62   MachineFunctionPass::getAnalysisUsage(AU);
63 }
64 
65 bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) {
66   if (skipFunction(F.getFunction()))
67     return false;
68 
69   TII = F.getSubtarget<SystemZSubtarget>().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.
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.
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.
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