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//===-- AArch64CleanupLocalDynamicTLSPass.cpp ---------------------*- C++ -*-=//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Local-dynamic access to thread-local variables proceeds in three stages.
// 1. The offset of this Module's thread-local area from TPIDR_EL0 is calculated
// in much the same way as a general-dynamic TLS-descriptor access against
// the special symbol _TLS_MODULE_BASE.
// 2. The variable's offset from _TLS_MODULE_BASE_ is calculated using
// instructions with "dtprel" modifiers.
// 3. These two are added, together with TPIDR_EL0, to obtain the variable's
// true address.
// This is only better than general-dynamic access to the variable if two or
// more of the first stage TLS-descriptor calculations can be combined. This
// pass looks through a function and performs such combinations.
#include "AArch64.h"
#include "AArch64InstrInfo.h"
#include "AArch64MachineFunctionInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
using namespace llvm;
#define TLSCLEANUP_PASS_NAME "AArch64 Local Dynamic TLS Access Clean-up"
namespace {
struct LDTLSCleanup : public MachineFunctionPass {
static char ID;
LDTLSCleanup() : MachineFunctionPass(ID) {
bool runOnMachineFunction(MachineFunction &MF) override {
if (skipFunction(MF.getFunction()))
return false;
AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
if (AFI->getNumLocalDynamicTLSAccesses() < 2) {
// No point folding accesses if there isn't at least two.
return false;
MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
return VisitNode(DT->getRootNode(), 0);
// Visit the dominator subtree rooted at Node in pre-order.
// If TLSBaseAddrReg is non-null, then use that to replace any
// TLS_base_addr instructions. Otherwise, create the register
// when the first such instruction is seen, and then use it
// as we encounter more instructions.
bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg) {
MachineBasicBlock *BB = Node->getBlock();
bool Changed = false;
// Traverse the current block.
for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;
++I) {
switch (I->getOpcode()) {
// Make sure it's a local dynamic access.
if (!I->getOperand(0).isSymbol() ||
strcmp(I->getOperand(0).getSymbolName(), "_TLS_MODULE_BASE_"))
if (TLSBaseAddrReg)
I = replaceTLSBaseAddrCall(*I, TLSBaseAddrReg);
I = setRegister(*I, &TLSBaseAddrReg);
Changed = true;
// Visit the children of this block in the dominator tree.
for (MachineDomTreeNode *N : *Node) {
Changed |= VisitNode(N, TLSBaseAddrReg);
return Changed;
// Replace the TLS_base_addr instruction I with a copy from
// TLSBaseAddrReg, returning the new instruction.
MachineInstr *replaceTLSBaseAddrCall(MachineInstr &I,
unsigned TLSBaseAddrReg) {
MachineFunction *MF = I.getParent()->getParent();
const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
// Insert a Copy from TLSBaseAddrReg to x0, which is where the rest of the
// code sequence assumes the address will be.
MachineInstr *Copy = BuildMI(*I.getParent(), I, I.getDebugLoc(),
TII->get(TargetOpcode::COPY), AArch64::X0)
// Erase the TLS_base_addr instruction.
return Copy;
// Create a virtual register in *TLSBaseAddrReg, and populate it by
// inserting a copy instruction after I. Returns the new instruction.
MachineInstr *setRegister(MachineInstr &I, unsigned *TLSBaseAddrReg) {
MachineFunction *MF = I.getParent()->getParent();
const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
// Create a virtual register for the TLS base address.
MachineRegisterInfo &RegInfo = MF->getRegInfo();
*TLSBaseAddrReg = RegInfo.createVirtualRegister(&AArch64::GPR64RegClass);
// Insert a copy from X0 to TLSBaseAddrReg for later.
MachineInstr *Copy =
BuildMI(*I.getParent(), ++I.getIterator(), I.getDebugLoc(),
TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
return Copy;
StringRef getPassName() const override { return TLSCLEANUP_PASS_NAME; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
INITIALIZE_PASS(LDTLSCleanup, "aarch64-local-dynamic-tls-cleanup",
char LDTLSCleanup::ID = 0;
FunctionPass *llvm::createAArch64CleanupLocalDynamicTLSPass() {
return new LDTLSCleanup();