LLVM 17.0.0git
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"
32using namespace llvm;
33
34#define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
35
36namespace {
37struct 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()) {
70 case AArch64::TLSDESC_CALLSEQ:
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();
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 // Update the call site info.
109 if (I.shouldUpdateCallSiteInfo())
110 I.getMF()->eraseCallSiteInfo(&I);
111
112 // Erase the TLS_base_addr instruction.
113 I.eraseFromParent();
114
115 return Copy;
116 }
117
118 // Create a virtual register in *TLSBaseAddrReg, and populate it by
119 // inserting a copy instruction after I. Returns the new instruction.
120 MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
121 MachineFunction *MF = I.getParent()->getParent();
123
124 // Create a virtual register for the TLS base address.
126 *TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
127
128 // Insert a copy from X0 to TLSBaseAddrReg for later.
129 MachineInstr *Copy =
130 BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
131 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
132 .addReg(AArch64::X0);
133
134 return Copy;
135 }
136
137 StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
138
139 void getAnalysisUsage(AnalysisUsage &AU) const override {
140 AU.setPreservesCFG();
143 }
144};
145}
146
147INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
148 TLSCLEANUP_PASS_NAME, false, false)
149
150char LDTLSCleanup::ID = 0;
152 return new LDTLSCleanup();
153}
#define TLSCLEANUP_PASS_NAME
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
const HexagonInstrInfo * TII
#define I(x, y, z)
Definition: MD5.cpp:58
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:38
AArch64FunctionInfo - This class is derived from MachineFunctionInfo and contains private AArch64-spe...
Represent the analysis usage information of a pass.
AnalysisUsage & addRequired()
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:265
Base class for the actual dominator tree node.
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:311
bool skipFunction(const Function &F) const
Optional passes call this function to check whether the pass should be skipped.
Definition: Pass.cpp:174
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...
MachineDomTreeNode * getRootNode() const
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
virtual bool runOnMachineFunction(MachineFunction &MF)=0
runOnMachineFunction - This method must be overloaded to perform the desired machine code transformat...
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
MachineRegisterInfo & getRegInfo()
getRegInfo - Return information about the registers currently in use.
Function & getFunction()
Return the LLVM function that this machine code represents.
Ty * getInfo()
getInfo - Keep track of various per-function pieces of information for backends that would like to do...
const MachineInstrBuilder & addReg(Register RegNo, unsigned flags=0, unsigned SubReg=0) const
Add a new virtual register operand.
Representation of each machine instruction.
Definition: MachineInstr.h:68
MachineRegisterInfo - Keep track of information for virtual and physical registers,...
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
virtual StringRef getPassName() const
getPassName - Return a nice clean name for a pass.
Definition: Pass.cpp:81
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
TargetInstrInfo - Interface to description of machine instruction set.
virtual const TargetInstrInfo * getInstrInfo() const
unsigned ID
LLVM IR allows to use arbitrary numbers as calling convention identifiers.
Definition: CallingConv.h:24
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
void initializeLDTLSCleanupPass(PassRegistry &)
MachineInstrBuilder BuildMI(MachineFunction &MF, const MIMetadata &MIMD, const MCInstrDesc &MCID)
Builder interface. Specify how to create the initial instruction itself.
FunctionPass * createAArch64CleanupLocalDynamicTLSPass()
#define N