LLVM  9.0.0svn
AArch64CleanupLocalDynamicTLSPass.cpp
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1 //===-- AArch64CleanupLocalDynamicTLSPass.cpp ---------------------*- C++ -*-=//
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 // Local-dynamic access to thread-local variables proceeds in three stages.
10 //
11 // 1. The offset of this Module's thread-local area from TPIDR_EL0 is calculated
12 // in much the same way as a general-dynamic TLS-descriptor access against
13 // the special symbol _TLS_MODULE_BASE.
14 // 2. The variable's offset from _TLS_MODULE_BASE_ is calculated using
15 // instructions with "dtprel" modifiers.
16 // 3. These two are added, together with TPIDR_EL0, to obtain the variable's
17 // true address.
18 //
19 // This is only better than general-dynamic access to the variable if two or
20 // more of the first stage TLS-descriptor calculations can be combined. This
21 // pass looks through a function and performs such combinations.
22 //
23 //===----------------------------------------------------------------------===//
24 #include "AArch64.h"
25 #include "AArch64InstrInfo.h"
32 using namespace llvm;
33 
34 #define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
35 
36 namespace {
37 struct LDTLSCleanup : public MachineFunctionPass {
38  static char ID;
39  LDTLSCleanup() : MachineFunctionPass(ID) {
41  }
42 
43  bool runOnMachineFunction(MachineFunction &MF) override {
44  if (skipFunction(MF.getFunction()))
45  return false;
46 
48  if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
49  // No point folding accesses if there isn't at least two.
50  return false;
51  }
52 
53  MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
54  return VisitNode(DT->getRootNode(), 0);
55  }
56 
57  // Visit the dominator subtree rooted at Node in pre-order.
58  // If TLSBaseAddrReg is non-null, then use that to replace any
59  // TLS_base_addr instructions. Otherwise, create the register
60  // when the first such instruction is seen, and then use it
61  // as we encounter more instructions.
62  bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
63  MachineBasicBlock *BB = Node->getBlock();
64  bool Changed = false;
65 
66  // Traverse the current block.
67  for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
68  ++I) {
69  switch (I->getOpcode()) {
71  // Make sure it's a local dynamic access.
72  if (!I->getOperand(0).isSymbol() ||
73  strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
74  break;
75 
76  if (TLSBaseAddrReg)
77  I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
78  else
79  I = setRegister(*I, &TLSBaseAddrReg);
80  Changed = true;
81  break;
82  default:
83  break;
84  }
85  }
86 
87  // Visit the children of this block in the dominator tree.
88  for (MachineDomTreeNode *N : *Node) {
89  Changed |= VisitNode(N, TLSBaseAddrReg);
90  }
91 
92  return Changed;
93  }
94 
95  // Replace the TLS_base_addr instruction I with a copy from
96  // TLSBaseAddrReg, returning the new instruction.
97  MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
98  unsigned TLSBaseAddrReg) {
99  MachineFunction *MF = I.getParent()->getParent();
100  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
101 
102  // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
103  // code sequence assumes the address will be.
104  MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
105  TII->get(TargetOpcode::COPY), AArch64::X0)
106  .addReg(TLSBaseAddrReg);
107 
108  // Erase the TLS_base_addr instruction.
109  I.eraseFromParent();
110 
111  return Copy;
112  }
113 
114  // Create a virtual register in *TLSBaseAddrReg, and populate it by
115  // inserting a copy instruction after I. Returns the new instruction.
116  MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
117  MachineFunction *MF = I.getParent()->getParent();
118  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
119 
120  // Create a virtual register for the TLS base address.
121  MachineRegisterInfo &RegInfo = MF->getRegInfo();
122  *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
123 
124  // Insert a copy from X0 to TLSBaseAddrReg for later.
125  MachineInstr *Copy =
126  BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
127  TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
128  .addReg(AArch64::X0);
129 
130  return Copy;
131  }
132 
133  StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
134 
135  void getAnalysisUsage(AnalysisUsage &AU) const override {
136  AU.setPreservesCFG();
139  }
140 };
141 }
142 
143 INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
144  TLSCLEANUP_PASS_NAME, false, false)
145 
146 char LDTLSCleanup::ID = 0;
148  return new LDTLSCleanup();
149 }
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
AArch64FunctionInfo - This class is derived from MachineFunctionInfo and contains private AArch64-spe...
This class represents lattice values for constants.
Definition: AllocatorList.h:23
Register createVirtualRegister(const TargetRegisterClass *RegClass, StringRef Name="")
createVirtualRegister - Create and return a new virtual register in the function with the specified r...
const DebugLoc & getDebugLoc() const
Returns the debug location id of this MachineInstr.
Definition: MachineInstr.h:384
AnalysisUsage & addRequired()
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
const HexagonInstrInfo * TII
void initializeLDTLSCleanupPass(PassRegistry &)
void eraseFromParent()
Unlink &#39;this&#39; from the containing basic block and delete it.
FunctionPass * createAArch64CleanupLocalDynamicTLSPass()
Base class for the actual dominator tree node.
virtual const TargetInstrInfo * getInstrInfo() const
TargetInstrInfo - Interface to description of machine instruction set.
MachineInstrBuilder BuildMI(MachineFunction &MF, const DebugLoc &DL, const MCInstrDesc &MCID)
Builder interface. Specify how to create the initial instruction itself.
NodeT * getBlock() const
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
Represent the analysis usage information of a pass.
Ty * getInfo()
getInfo - Keep track of various per-function pieces of information for backends that would like to do...
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:284
self_iterator getIterator()
Definition: ilist_node.h:81
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:33
MachineDomTreeNode * getRootNode() const
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:301
const Function & getFunction() const
Return the LLVM function that this machine code represents.
const MachineBasicBlock * getParent() const
Definition: MachineInstr.h:255
MachineRegisterInfo - Keep track of information for virtual and physical registers, including vreg register classes, use/def chains for registers, etc.
Representation of each machine instruction.
Definition: MachineInstr.h:63
const MachineFunction * getParent() const
Return the MachineFunction containing this basic block.
#define TLSCLEANUP_PASS_NAME
MachineRegisterInfo & getRegInfo()
getRegInfo - Return information about the registers currently in use.
const MCInstrDesc & get(unsigned Opcode) const
Return the machine instruction descriptor that corresponds to the specified instruction opcode...
Definition: MCInstrInfo.h:44
#define I(x, y, z)
Definition: MD5.cpp:58
#define N
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...