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| //===-- SystemZLDCleanup.cpp - Clean up local-dynamic TLS accesses --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass combines multiple accesses to local-dynamic TLS variables so that
// the TLS base address for the module is only fetched once per execution path
// through the function.
//
//===----------------------------------------------------------------------===//
#include "SystemZMachineFunctionInfo.h"
#include "SystemZTargetMachine.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
namespace {
class SystemZLDCleanup : public MachineFunctionPass {
public:
static char ID;
SystemZLDCleanup(const SystemZTargetMachine &tm)
: MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {}
StringRef getPassName() const override {
return "SystemZ Local Dynamic TLS Access Clean-up";
}
bool runOnMachineFunction(MachineFunction &MF) override;
void getAnalysisUsage(AnalysisUsage &AU) const override;
private:
bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg);
MachineInstr *ReplaceTLSCall(MachineInstr *I, unsigned TLSBaseAddrReg);
MachineInstr *SetRegister(MachineInstr *I, unsigned *TLSBaseAddrReg);
const SystemZInstrInfo *TII;
MachineFunction *MF;
};
char SystemZLDCleanup::ID = 0;
} // end anonymous namespace
FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
return new SystemZLDCleanup(TM);
}
void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<MachineDominatorTree>();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) {
if (skipFunction(F.getFunction()))
return false;
TII = static_cast<const SystemZInstrInfo *>(F.getSubtarget().getInstrInfo());
MF = &F;
SystemZMachineFunctionInfo* MFI = F.getInfo<SystemZMachineFunctionInfo>();
if (MFI->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_LDCALL instructions. Otherwise, create the register
// when the first such instruction is seen, and then use it
// as we encounter more instructions.
bool SystemZLDCleanup::VisitNode(MachineDomTreeNode *Node,
unsigned TLSBaseAddrReg) {
MachineBasicBlock *BB = Node->getBlock();
bool Changed = false;
// Traverse the current block.
for (auto I = BB->begin(), E = BB->end(); I != E; ++I) {
switch (I->getOpcode()) {
case SystemZ::TLS_LDCALL:
if (TLSBaseAddrReg)
I = ReplaceTLSCall(&*I, TLSBaseAddrReg);
else
I = SetRegister(&*I, &TLSBaseAddrReg);
Changed = true;
break;
default:
break;
}
}
// Visit the children of this block in the dominator tree.
for (auto I = Node->begin(), E = Node->end(); I != E; ++I)
Changed |= VisitNode(*I, TLSBaseAddrReg);
return Changed;
}
// Replace the TLS_LDCALL instruction I with a copy from TLSBaseAddrReg,
// returning the new instruction.
MachineInstr *SystemZLDCleanup::ReplaceTLSCall(MachineInstr *I,
unsigned TLSBaseAddrReg) {
// Insert a Copy from TLSBaseAddrReg to R2.
MachineInstr *Copy = BuildMI(*I->getParent(), I, I->getDebugLoc(),
TII->get(TargetOpcode::COPY), SystemZ::R2D)
.addReg(TLSBaseAddrReg);
// Erase the TLS_LDCALL instruction.
I->eraseFromParent();
return Copy;
}
// Create a virtual register in *TLSBaseAddrReg, and populate it by
// inserting a copy instruction after I. Returns the new instruction.
MachineInstr *SystemZLDCleanup::SetRegister(MachineInstr *I,
unsigned *TLSBaseAddrReg) {
// Create a virtual register for the TLS base address.
MachineRegisterInfo &RegInfo = MF->getRegInfo();
*TLSBaseAddrReg = RegInfo.createVirtualRegister(&SystemZ::GR64BitRegClass);
// Insert a copy from R2 to TLSBaseAddrReg.
MachineInstr *Next = I->getNextNode();
MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(),
TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
.addReg(SystemZ::R2D);
return Copy;
}
|