LLVM  8.0.0svn
AArch64CleanupLocalDynamicTLSPass.cpp
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1 //===-- AArch64CleanupLocalDynamicTLSPass.cpp ---------------------*- C++ -*-=//
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 // Local-dynamic access to thread-local variables proceeds in three stages.
11 //
12 // 1. The offset of this Module's thread-local area from TPIDR_EL0 is calculated
13 // in much the same way as a general-dynamic TLS-descriptor access against
14 // the special symbol _TLS_MODULE_BASE.
15 // 2. The variable's offset from _TLS_MODULE_BASE_ is calculated using
16 // instructions with "dtprel" modifiers.
17 // 3. These two are added, together with TPIDR_EL0, to obtain the variable's
18 // true address.
19 //
20 // This is only better than general-dynamic access to the variable if two or
21 // more of the first stage TLS-descriptor calculations can be combined. This
22 // pass looks through a function and performs such combinations.
23 //
24 //===----------------------------------------------------------------------===//
25 #include "AArch64.h"
26 #include "AArch64InstrInfo.h"
33 using namespace llvm;
34 
35 #define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
36 
37 namespace {
38 struct LDTLSCleanup : public MachineFunctionPass {
39  static char ID;
40  LDTLSCleanup() : MachineFunctionPass(ID) {
42  }
43 
44  bool runOnMachineFunction(MachineFunction &MF) override {
45  if (skipFunction(MF.getFunction()))
46  return false;
47 
49  if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
50  // No point folding accesses if there isn't at least two.
51  return false;
52  }
53 
54  MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
55  return VisitNode(DT->getRootNode(), 0);
56  }
57 
58  // Visit the dominator subtree rooted at Node in pre-order.
59  // If TLSBaseAddrReg is non-null, then use that to replace any
60  // TLS_base_addr instructions. Otherwise, create the register
61  // when the first such instruction is seen, and then use it
62  // as we encounter more instructions.
63  bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
64  MachineBasicBlock *BB = Node->getBlock();
65  bool Changed = false;
66 
67  // Traverse the current block.
68  for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
69  ++I) {
70  switch (I->getOpcode()) {
72  // Make sure it's a local dynamic access.
73  if (!I->getOperand(0).isSymbol() ||
74  strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
75  break;
76 
77  if (TLSBaseAddrReg)
78  I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
79  else
80  I = setRegister(*I, &TLSBaseAddrReg);
81  Changed = true;
82  break;
83  default:
84  break;
85  }
86  }
87 
88  // Visit the children of this block in the dominator tree.
89  for (MachineDomTreeNode *N : *Node) {
90  Changed |= VisitNode(N, TLSBaseAddrReg);
91  }
92 
93  return Changed;
94  }
95 
96  // Replace the TLS_base_addr instruction I with a copy from
97  // TLSBaseAddrReg, returning the new instruction.
98  MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
99  unsigned TLSBaseAddrReg) {
100  MachineFunction *MF = I.getParent()->getParent();
101  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
102 
103  // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
104  // code sequence assumes the address will be.
105  MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
106  TII->get(TargetOpcode::COPY), AArch64::X0)
107  .addReg(TLSBaseAddrReg);
108 
109  // Erase the TLS_base_addr instruction.
110  I.eraseFromParent();
111 
112  return Copy;
113  }
114 
115  // Create a virtual register in *TLSBaseAddrReg, and populate it by
116  // inserting a copy instruction after I. Returns the new instruction.
117  MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
118  MachineFunction *MF = I.getParent()->getParent();
119  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
120 
121  // Create a virtual register for the TLS base address.
122  MachineRegisterInfo &RegInfo = MF->getRegInfo();
123  *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
124 
125  // Insert a copy from X0 to TLSBaseAddrReg for later.
126  MachineInstr *Copy =
127  BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
128  TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
129  .addReg(AArch64::X0);
130 
131  return Copy;
132  }
133 
134  StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
135 
136  void getAnalysisUsage(AnalysisUsage &AU) const override {
137  AU.setPreservesCFG();
140  }
141 };
142 }
143 
144 INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
145  TLSCLEANUP_PASS_NAME, false, false)
146 
147 char LDTLSCleanup::ID = 0;
149  return new LDTLSCleanup();
150 }
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...
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
const DebugLoc & getDebugLoc() const
Returns the debug location id of this MachineInstr.
Definition: MachineInstr.h:383
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:285
self_iterator getIterator()
Definition: ilist_node.h:82
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:34
MachineDomTreeNode * getRootNode() const
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:286
const Function & getFunction() const
Return the LLVM function that this machine code represents.
const MachineBasicBlock * getParent() const
Definition: MachineInstr.h:254
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:64
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:45
#define I(x, y, z)
Definition: MD5.cpp:58
#define N
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...
unsigned createVirtualRegister(const TargetRegisterClass *RegClass, StringRef Name="")
createVirtualRegister - Create and return a new virtual register in the function with the specified r...