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//=- MachineLoopUtils.cpp - Functions for manipulating loops ----------------=//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineLoopUtils.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
using namespace llvm;
namespace {
// MI's parent and BB are clones of each other. Find the equivalent copy of MI
// in BB.
MachineInstr &findEquivalentInstruction(MachineInstr &MI,
MachineBasicBlock *BB) {
MachineBasicBlock *PB = MI.getParent();
unsigned Offset = std::distance(PB->instr_begin(), MachineBasicBlock::instr_iterator(MI));
return *std::next(BB->instr_begin(), Offset);
}
} // namespace
MachineBasicBlock *llvm::PeelSingleBlockLoop(LoopPeelDirection Direction,
MachineBasicBlock *Loop,
MachineRegisterInfo &MRI,
const TargetInstrInfo *TII) {
MachineFunction &MF = *Loop->getParent();
MachineBasicBlock *Preheader = *Loop->pred_begin();
if (Preheader == Loop)
Preheader = *std::next(Loop->pred_begin());
MachineBasicBlock *Exit = *Loop->succ_begin();
if (Exit == Loop)
Exit = *std::next(Loop->succ_begin());
MachineBasicBlock *NewBB = MF.CreateMachineBasicBlock(Loop->getBasicBlock());
if (Direction == LPD_Front)
MF.insert(Loop->getIterator(), NewBB);
else
MF.insert(std::next(Loop->getIterator()), NewBB);
DenseMap<Register, Register> Remaps;
auto InsertPt = NewBB->end();
for (MachineInstr &MI : *Loop) {
MachineInstr *NewMI = MF.CloneMachineInstr(&MI);
NewBB->insert(InsertPt, NewMI);
for (MachineOperand &MO : NewMI->defs()) {
Register OrigR = MO.getReg();
if (OrigR.isPhysical())
continue;
Register &R = Remaps[OrigR];
R = MRI.createVirtualRegister(MRI.getRegClass(OrigR));
MO.setReg(R);
if (Direction == LPD_Back) {
// Replace all uses outside the original loop with the new register.
// FIXME: is the use_iterator stable enough to mutate register uses
// while iterating?
SmallVector<MachineOperand *, 4> Uses;
for (auto &Use : MRI.use_operands(OrigR))
if (Use.getParent()->getParent() != Loop)
Uses.push_back(&Use);
for (auto *Use : Uses) {
MRI.constrainRegClass(R, MRI.getRegClass(Use->getReg()));
Use->setReg(R);
}
}
}
}
for (auto I = NewBB->getFirstNonPHI(); I != NewBB->end(); ++I)
for (MachineOperand &MO : I->uses())
if (MO.isReg() && Remaps.count(MO.getReg()))
MO.setReg(Remaps[MO.getReg()]);
for (auto I = NewBB->begin(); I->isPHI(); ++I) {
MachineInstr &MI = *I;
unsigned LoopRegIdx = 3, InitRegIdx = 1;
if (MI.getOperand(2).getMBB() != Preheader)
std::swap(LoopRegIdx, InitRegIdx);
MachineInstr &OrigPhi = findEquivalentInstruction(MI, Loop);
assert(OrigPhi.isPHI());
if (Direction == LPD_Front) {
// When peeling front, we are only left with the initial value from the
// preheader.
Register R = MI.getOperand(LoopRegIdx).getReg();
if (Remaps.count(R))
R = Remaps[R];
OrigPhi.getOperand(InitRegIdx).setReg(R);
MI.RemoveOperand(LoopRegIdx + 1);
MI.RemoveOperand(LoopRegIdx + 0);
} else {
// When peeling back, the initial value is the loop-carried value from
// the original loop.
Register LoopReg = OrigPhi.getOperand(LoopRegIdx).getReg();
MI.getOperand(LoopRegIdx).setReg(LoopReg);
MI.RemoveOperand(InitRegIdx + 1);
MI.RemoveOperand(InitRegIdx + 0);
}
}
DebugLoc DL;
if (Direction == LPD_Front) {
Preheader->replaceSuccessor(Loop, NewBB);
NewBB->addSuccessor(Loop);
Loop->replacePhiUsesWith(Preheader, NewBB);
if (TII->removeBranch(*Preheader) > 0)
TII->insertBranch(*Preheader, NewBB, nullptr, {}, DL);
TII->removeBranch(*NewBB);
TII->insertBranch(*NewBB, Loop, nullptr, {}, DL);
} else {
Loop->replaceSuccessor(Exit, NewBB);
Exit->replacePhiUsesWith(Loop, NewBB);
NewBB->addSuccessor(Exit);
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
bool CanAnalyzeBr = !TII->analyzeBranch(*Loop, TBB, FBB, Cond);
(void)CanAnalyzeBr;
assert(CanAnalyzeBr && "Must be able to analyze the loop branch!");
TII->removeBranch(*Loop);
TII->insertBranch(*Loop, TBB == Exit ? NewBB : TBB,
FBB == Exit ? NewBB : FBB, Cond, DL);
if (TII->removeBranch(*NewBB) > 0)
TII->insertBranch(*NewBB, Exit, nullptr, {}, DL);
}
return NewBB;
}
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