LLVM  6.0.0svn
SystemZLDCleanup.cpp
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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 
17 #include "SystemZTargetMachine.h"
25 
26 using namespace llvm;
27 
28 namespace {
29 
30 class SystemZLDCleanup : public MachineFunctionPass {
31 public:
32  static char ID;
33  SystemZLDCleanup(const SystemZTargetMachine &tm)
34  : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {}
35 
36  StringRef 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 
57  return new SystemZLDCleanup(TM);
58 }
59 
60 void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
61  AU.setPreservesCFG();
64 }
65 
66 bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) {
67  if (skipFunction(*F.getFunction()))
68  return false;
69 
70  TII = static_cast<const SystemZInstrInfo *>(F.getSubtarget().getInstrInfo());
71  MF = &F;
72 
74  if (MFI->getNumLocalDynamicTLSAccesses() < 2) {
75  // No point folding accesses if there isn't at least two.
76  return false;
77  }
78 
79  MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
80  return VisitNode(DT->getRootNode(), 0);
81 }
82 
83 // Visit the dominator subtree rooted at Node in pre-order.
84 // If TLSBaseAddrReg is non-null, then use that to replace any
85 // TLS_LDCALL instructions. Otherwise, create the register
86 // when the first such instruction is seen, and then use it
87 // as we encounter more instructions.
88 bool SystemZLDCleanup::VisitNode(MachineDomTreeNode *Node,
89  unsigned TLSBaseAddrReg) {
90  MachineBasicBlock *BB = Node->getBlock();
91  bool Changed = false;
92 
93  // Traverse the current block.
94  for (auto I = BB->begin(), E = BB->end(); I != E; ++I) {
95  switch (I->getOpcode()) {
97  if (TLSBaseAddrReg)
98  I = ReplaceTLSCall(&*I, TLSBaseAddrReg);
99  else
100  I = SetRegister(&*I, &TLSBaseAddrReg);
101  Changed = true;
102  break;
103  default:
104  break;
105  }
106  }
107 
108  // Visit the children of this block in the dominator tree.
109  for (auto I = Node->begin(), E = Node->end(); I != E; ++I)
110  Changed |= VisitNode(*I, TLSBaseAddrReg);
111 
112  return Changed;
113 }
114 
115 // Replace the TLS_LDCALL instruction I with a copy from TLSBaseAddrReg,
116 // returning the new instruction.
117 MachineInstr *SystemZLDCleanup::ReplaceTLSCall(MachineInstr *I,
118  unsigned TLSBaseAddrReg) {
119  // Insert a Copy from TLSBaseAddrReg to R2.
120  MachineInstr *Copy = BuildMI(*I->getParent(), I, I->getDebugLoc(),
121  TII->get(TargetOpcode::COPY), SystemZ::R2D)
122  .addReg(TLSBaseAddrReg);
123 
124  // Erase the TLS_LDCALL instruction.
125  I->eraseFromParent();
126 
127  return Copy;
128 }
129 
130 // Create a virtual register in *TLSBaseAddrReg, and populate it by
131 // inserting a copy instruction after I. Returns the new instruction.
132 MachineInstr *SystemZLDCleanup::SetRegister(MachineInstr *I,
133  unsigned *TLSBaseAddrReg) {
134  // Create a virtual register for the TLS base address.
135  MachineRegisterInfo &RegInfo = MF->getRegInfo();
136  *TLSBaseAddrReg = RegInfo.createVirtualRegister(&SystemZ::GR64BitRegClass);
137 
138  // Insert a copy from R2 to TLSBaseAddrReg.
139  MachineInstr *Next = I->getNextNode();
140  MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(),
141  TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
142  .addReg(SystemZ::R2D);
143 
144  return Copy;
145 }
146 
NodeTy * getNextNode()
Get the next node, or nullptr for the list tail.
Definition: ilist_node.h:289
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:268
F(f)
AnalysisUsage & addRequired()
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
const HexagonInstrInfo * TII
void eraseFromParent()
Unlink &#39;this&#39; from the containing basic block and delete it.
Base class for the actual dominator tree node.
virtual const TargetInstrInfo * getInstrInfo() const
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
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:139
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:59
FunctionPass * createSystemZLDCleanupPass(SystemZTargetMachine &TM)
#define I(x, y, z)
Definition: MD5.cpp:58
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...