LLVM  6.0.0svn
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"
28 #include "AArch64TargetMachine.h"
34 using namespace llvm;
35 
36 #define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
37 
38 namespace {
39 struct LDTLSCleanup : public MachineFunctionPass {
40  static char ID;
41  LDTLSCleanup() : MachineFunctionPass(ID) {
43  }
44 
45  bool runOnMachineFunction(MachineFunction &MF) override {
46  if (skipFunction(*MF.getFunction()))
47  return false;
48 
50  if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
51  // No point folding accesses if there isn't at least two.
52  return false;
53  }
54 
55  MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
56  return VisitNode(DT->getRootNode(), 0);
57  }
58 
59  // Visit the dominator subtree rooted at Node in pre-order.
60  // If TLSBaseAddrReg is non-null, then use that to replace any
61  // TLS_base_addr instructions. Otherwise, create the register
62  // when the first such instruction is seen, and then use it
63  // as we encounter more instructions.
64  bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
65  MachineBasicBlock *BB = Node->getBlock();
66  bool Changed = false;
67 
68  // Traverse the current block.
69  for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
70  ++I) {
71  switch (I->getOpcode()) {
73  // Make sure it's a local dynamic access.
74  if (!I->getOperand(0).isSymbol() ||
75  strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
76  break;
77 
78  if (TLSBaseAddrReg)
79  I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
80  else
81  I = setRegister(*I, &TLSBaseAddrReg);
82  Changed = true;
83  break;
84  default:
85  break;
86  }
87  }
88 
89  // Visit the children of this block in the dominator tree.
90  for (MachineDomTreeNode *N : *Node) {
91  Changed |= VisitNode(N, TLSBaseAddrReg);
92  }
93 
94  return Changed;
95  }
96 
97  // Replace the TLS_base_addr instruction I with a copy from
98  // TLSBaseAddrReg, returning the new instruction.
99  MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
100  unsigned TLSBaseAddrReg) {
101  MachineFunction *MF = I.getParent()->getParent();
102  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
103 
104  // Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
105  // code sequence assumes the address will be.
106  MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
107  TII->get(TargetOpcode::COPY), AArch64::X0)
108  .addReg(TLSBaseAddrReg);
109 
110  // Erase the TLS_base_addr instruction.
111  I.eraseFromParent();
112 
113  return Copy;
114  }
115 
116  // Create a virtual register in *TLSBaseAddrReg, and populate it by
117  // inserting a copy instruction after I. Returns the new instruction.
118  MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
119  MachineFunction *MF = I.getParent()->getParent();
120  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
121 
122  // Create a virtual register for the TLS base address.
123  MachineRegisterInfo &RegInfo = MF->getRegInfo();
124  *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
125 
126  // Insert a copy from X0 to TLSBaseAddrReg for later.
127  MachineInstr *Copy =
128  BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
129  TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
130  .addReg(AArch64::X0);
131 
132  return Copy;
133  }
134 
135  StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
136 
137  void getAnalysisUsage(AnalysisUsage &AU) const override {
138  AU.setPreservesCFG();
141  }
142 };
143 }
144 
145 INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
146  TLSCLEANUP_PASS_NAME, false, false)
147 
148 char LDTLSCleanup::ID = 0;
150  return new LDTLSCleanup();
151 }
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
unsigned createVirtualRegister(const TargetRegisterClass *RegClass)
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:269
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:285
const MachineBasicBlock * getParent() const
Definition: MachineInstr.h:140
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:60
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
const Function * getFunction() const
getFunction - Return the LLVM function that this machine code represents
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...