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llvm-project/llvm/lib/CodeGen/ModuloSchedule.cpp

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//===- ModuloSchedule.cpp - Software pipeline schedule expansion ----------===//
//
// 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/ModuloSchedule.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/MC/MCContext.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#define DEBUG_TYPE "pipeliner"
using namespace llvm;
void ModuloSchedule::print(raw_ostream &OS) {
for (MachineInstr *MI : ScheduledInstrs)
OS << "[stage " << getStage(MI) << " @" << getCycle(MI) << "c] " << *MI;
}
//===----------------------------------------------------------------------===//
// ModuloScheduleExpander implementation
//===----------------------------------------------------------------------===//
/// Return the register values for the operands of a Phi instruction.
/// This function assume the instruction is a Phi.
static void getPhiRegs(MachineInstr &Phi, MachineBasicBlock *Loop,
unsigned &InitVal, unsigned &LoopVal) {
assert(Phi.isPHI() && "Expecting a Phi.");
InitVal = 0;
LoopVal = 0;
for (unsigned i = 1, e = Phi.getNumOperands(); i != e; i += 2)
if (Phi.getOperand(i + 1).getMBB() != Loop)
InitVal = Phi.getOperand(i).getReg();
else
LoopVal = Phi.getOperand(i).getReg();
assert(InitVal != 0 && LoopVal != 0 && "Unexpected Phi structure.");
}
/// Return the Phi register value that comes from the incoming block.
static unsigned getInitPhiReg(MachineInstr &Phi, MachineBasicBlock *LoopBB) {
for (unsigned i = 1, e = Phi.getNumOperands(); i != e; i += 2)
if (Phi.getOperand(i + 1).getMBB() != LoopBB)
return Phi.getOperand(i).getReg();
return 0;
}
/// Return the Phi register value that comes the loop block.
static unsigned getLoopPhiReg(MachineInstr &Phi, MachineBasicBlock *LoopBB) {
for (unsigned i = 1, e = Phi.getNumOperands(); i != e; i += 2)
if (Phi.getOperand(i + 1).getMBB() == LoopBB)
return Phi.getOperand(i).getReg();
return 0;
}
void ModuloScheduleExpander::expand() {
BB = Schedule.getLoop()->getTopBlock();
Preheader = *BB->pred_begin();
if (Preheader == BB)
Preheader = *std::next(BB->pred_begin());
// Iterate over the definitions in each instruction, and compute the
// stage difference for each use. Keep the maximum value.
for (MachineInstr *MI : Schedule.getInstructions()) {
int DefStage = Schedule.getStage(MI);
for (const MachineOperand &Op : MI->operands()) {
if (!Op.isReg() || !Op.isDef())
continue;
Register Reg = Op.getReg();
unsigned MaxDiff = 0;
bool PhiIsSwapped = false;
for (MachineOperand &UseOp : MRI.use_operands(Reg)) {
MachineInstr *UseMI = UseOp.getParent();
int UseStage = Schedule.getStage(UseMI);
unsigned Diff = 0;
if (UseStage != -1 && UseStage >= DefStage)
Diff = UseStage - DefStage;
if (MI->isPHI()) {
if (isLoopCarried(*MI))
++Diff;
else
PhiIsSwapped = true;
}
MaxDiff = std::max(Diff, MaxDiff);
}
RegToStageDiff[Reg] = std::make_pair(MaxDiff, PhiIsSwapped);
}
}
generatePipelinedLoop();
}
void ModuloScheduleExpander::generatePipelinedLoop() {
LoopInfo = TII->analyzeLoopForPipelining(BB);
assert(LoopInfo && "Must be able to analyze loop!");
// Create a new basic block for the kernel and add it to the CFG.
MachineBasicBlock *KernelBB = MF.CreateMachineBasicBlock(BB->getBasicBlock());
unsigned MaxStageCount = Schedule.getNumStages() - 1;
// Remember the registers that are used in different stages. The index is
// the iteration, or stage, that the instruction is scheduled in. This is
// a map between register names in the original block and the names created
// in each stage of the pipelined loop.
ValueMapTy *VRMap = new ValueMapTy[(MaxStageCount + 1) * 2];
InstrMapTy InstrMap;
SmallVector<MachineBasicBlock *, 4> PrologBBs;
// Generate the prolog instructions that set up the pipeline.
generateProlog(MaxStageCount, KernelBB, VRMap, PrologBBs);
MF.insert(BB->getIterator(), KernelBB);
// Rearrange the instructions to generate the new, pipelined loop,
// and update register names as needed.
for (MachineInstr *CI : Schedule.getInstructions()) {
if (CI->isPHI())
continue;
unsigned StageNum = Schedule.getStage(CI);
MachineInstr *NewMI = cloneInstr(CI, MaxStageCount, StageNum);
updateInstruction(NewMI, false, MaxStageCount, StageNum, VRMap);
KernelBB->push_back(NewMI);
InstrMap[NewMI] = CI;
}
// Copy any terminator instructions to the new kernel, and update
// names as needed.
for (MachineInstr &MI : BB->terminators()) {
MachineInstr *NewMI = MF.CloneMachineInstr(&MI);
updateInstruction(NewMI, false, MaxStageCount, 0, VRMap);
KernelBB->push_back(NewMI);
InstrMap[NewMI] = &MI;
}
NewKernel = KernelBB;
KernelBB->transferSuccessors(BB);
KernelBB->replaceSuccessor(BB, KernelBB);
generateExistingPhis(KernelBB, PrologBBs.back(), KernelBB, KernelBB, VRMap,
InstrMap, MaxStageCount, MaxStageCount, false);
generatePhis(KernelBB, PrologBBs.back(), KernelBB, KernelBB, VRMap, InstrMap,
MaxStageCount, MaxStageCount, false);
LLVM_DEBUG(dbgs() << "New block\n"; KernelBB->dump(););
SmallVector<MachineBasicBlock *, 4> EpilogBBs;
// Generate the epilog instructions to complete the pipeline.
generateEpilog(MaxStageCount, KernelBB, VRMap, EpilogBBs, PrologBBs);
// We need this step because the register allocation doesn't handle some
// situations well, so we insert copies to help out.
splitLifetimes(KernelBB, EpilogBBs);
// Remove dead instructions due to loop induction variables.
removeDeadInstructions(KernelBB, EpilogBBs);
// Add branches between prolog and epilog blocks.
addBranches(*Preheader, PrologBBs, KernelBB, EpilogBBs, VRMap);
delete[] VRMap;
}
void ModuloScheduleExpander::cleanup() {
// Remove the original loop since it's no longer referenced.
for (auto &I : *BB)
LIS.RemoveMachineInstrFromMaps(I);
BB->clear();
BB->eraseFromParent();
}
/// Generate the pipeline prolog code.
void ModuloScheduleExpander::generateProlog(unsigned LastStage,
MachineBasicBlock *KernelBB,
ValueMapTy *VRMap,
MBBVectorTy &PrologBBs) {
MachineBasicBlock *PredBB = Preheader;
InstrMapTy InstrMap;
// Generate a basic block for each stage, not including the last stage,
// which will be generated in the kernel. Each basic block may contain
// instructions from multiple stages/iterations.
for (unsigned i = 0; i < LastStage; ++i) {
// Create and insert the prolog basic block prior to the original loop
// basic block. The original loop is removed later.
MachineBasicBlock *NewBB = MF.CreateMachineBasicBlock(BB->getBasicBlock());
PrologBBs.push_back(NewBB);
MF.insert(BB->getIterator(), NewBB);
NewBB->transferSuccessors(PredBB);
PredBB->addSuccessor(NewBB);
PredBB = NewBB;
// Generate instructions for each appropriate stage. Process instructions
// in original program order.
for (int StageNum = i; StageNum >= 0; --StageNum) {
for (MachineBasicBlock::iterator BBI = BB->instr_begin(),
BBE = BB->getFirstTerminator();
BBI != BBE; ++BBI) {
if (Schedule.getStage(&*BBI) == StageNum) {
if (BBI->isPHI())
continue;
MachineInstr *NewMI =
cloneAndChangeInstr(&*BBI, i, (unsigned)StageNum);
updateInstruction(NewMI, false, i, (unsigned)StageNum, VRMap);
NewBB->push_back(NewMI);
InstrMap[NewMI] = &*BBI;
}
}
}
rewritePhiValues(NewBB, i, VRMap, InstrMap);
LLVM_DEBUG({
dbgs() << "prolog:\n";
NewBB->dump();
});
}
PredBB->replaceSuccessor(BB, KernelBB);
// Check if we need to remove the branch from the preheader to the original
// loop, and replace it with a branch to the new loop.
unsigned numBranches = TII->removeBranch(*Preheader);
if (numBranches) {
SmallVector<MachineOperand, 0> Cond;
TII->insertBranch(*Preheader, PrologBBs[0], nullptr, Cond, DebugLoc());
}
}
/// Generate the pipeline epilog code. The epilog code finishes the iterations
/// that were started in either the prolog or the kernel. We create a basic
/// block for each stage that needs to complete.
void ModuloScheduleExpander::generateEpilog(unsigned LastStage,
MachineBasicBlock *KernelBB,
ValueMapTy *VRMap,
MBBVectorTy &EpilogBBs,
MBBVectorTy &PrologBBs) {
// We need to change the branch from the kernel to the first epilog block, so
// this call to analyze branch uses the kernel rather than the original BB.
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
bool checkBranch = TII->analyzeBranch(*KernelBB, TBB, FBB, Cond);
assert(!checkBranch && "generateEpilog must be able to analyze the branch");
if (checkBranch)
return;
MachineBasicBlock::succ_iterator LoopExitI = KernelBB->succ_begin();
if (*LoopExitI == KernelBB)
++LoopExitI;
assert(LoopExitI != KernelBB->succ_end() && "Expecting a successor");
MachineBasicBlock *LoopExitBB = *LoopExitI;
MachineBasicBlock *PredBB = KernelBB;
MachineBasicBlock *EpilogStart = LoopExitBB;
InstrMapTy InstrMap;
// Generate a basic block for each stage, not including the last stage,
// which was generated for the kernel. Each basic block may contain
// instructions from multiple stages/iterations.
int EpilogStage = LastStage + 1;
for (unsigned i = LastStage; i >= 1; --i, ++EpilogStage) {
MachineBasicBlock *NewBB = MF.CreateMachineBasicBlock();
EpilogBBs.push_back(NewBB);
MF.insert(BB->getIterator(), NewBB);
PredBB->replaceSuccessor(LoopExitBB, NewBB);
NewBB->addSuccessor(LoopExitBB);
if (EpilogStart == LoopExitBB)
EpilogStart = NewBB;
// Add instructions to the epilog depending on the current block.
// Process instructions in original program order.
for (unsigned StageNum = i; StageNum <= LastStage; ++StageNum) {
for (auto &BBI : *BB) {
if (BBI.isPHI())
continue;
MachineInstr *In = &BBI;
if ((unsigned)Schedule.getStage(In) == StageNum) {
// Instructions with memoperands in the epilog are updated with
// conservative values.
MachineInstr *NewMI = cloneInstr(In, UINT_MAX, 0);
updateInstruction(NewMI, i == 1, EpilogStage, 0, VRMap);
NewBB->push_back(NewMI);
InstrMap[NewMI] = In;
}
}
}
generateExistingPhis(NewBB, PrologBBs[i - 1], PredBB, KernelBB, VRMap,
InstrMap, LastStage, EpilogStage, i == 1);
generatePhis(NewBB, PrologBBs[i - 1], PredBB, KernelBB, VRMap, InstrMap,
LastStage, EpilogStage, i == 1);
PredBB = NewBB;
LLVM_DEBUG({
dbgs() << "epilog:\n";
NewBB->dump();
});
}
// Fix any Phi nodes in the loop exit block.
LoopExitBB->replacePhiUsesWith(BB, PredBB);
// Create a branch to the new epilog from the kernel.
// Remove the original branch and add a new branch to the epilog.
TII->removeBranch(*KernelBB);
TII->insertBranch(*KernelBB, KernelBB, EpilogStart, Cond, DebugLoc());
// Add a branch to the loop exit.
if (EpilogBBs.size() > 0) {
MachineBasicBlock *LastEpilogBB = EpilogBBs.back();
SmallVector<MachineOperand, 4> Cond1;
TII->insertBranch(*LastEpilogBB, LoopExitBB, nullptr, Cond1, DebugLoc());
}
}
/// Replace all uses of FromReg that appear outside the specified
/// basic block with ToReg.
static void replaceRegUsesAfterLoop(unsigned FromReg, unsigned ToReg,
MachineBasicBlock *MBB,
MachineRegisterInfo &MRI,
LiveIntervals &LIS) {
for (MachineOperand &O :
llvm::make_early_inc_range(MRI.use_operands(FromReg)))
if (O.getParent()->getParent() != MBB)
O.setReg(ToReg);
if (!LIS.hasInterval(ToReg))
LIS.createEmptyInterval(ToReg);
}
/// Return true if the register has a use that occurs outside the
/// specified loop.
static bool hasUseAfterLoop(unsigned Reg, MachineBasicBlock *BB,
MachineRegisterInfo &MRI) {
for (const MachineOperand &MO : MRI.use_operands(Reg))
if (MO.getParent()->getParent() != BB)
return true;
return false;
}
/// Generate Phis for the specific block in the generated pipelined code.
/// This function looks at the Phis from the original code to guide the
/// creation of new Phis.
void ModuloScheduleExpander::generateExistingPhis(
MachineBasicBlock *NewBB, MachineBasicBlock *BB1, MachineBasicBlock *BB2,
MachineBasicBlock *KernelBB, ValueMapTy *VRMap, InstrMapTy &InstrMap,
unsigned LastStageNum, unsigned CurStageNum, bool IsLast) {
// Compute the stage number for the initial value of the Phi, which
// comes from the prolog. The prolog to use depends on to which kernel/
// epilog that we're adding the Phi.
unsigned PrologStage = 0;
unsigned PrevStage = 0;
bool InKernel = (LastStageNum == CurStageNum);
if (InKernel) {
PrologStage = LastStageNum - 1;
PrevStage = CurStageNum;
} else {
PrologStage = LastStageNum - (CurStageNum - LastStageNum);
PrevStage = LastStageNum + (CurStageNum - LastStageNum) - 1;
}
for (MachineBasicBlock::iterator BBI = BB->instr_begin(),
BBE = BB->getFirstNonPHI();
BBI != BBE; ++BBI) {
Register Def = BBI->getOperand(0).getReg();
unsigned InitVal = 0;
unsigned LoopVal = 0;
getPhiRegs(*BBI, BB, InitVal, LoopVal);
unsigned PhiOp1 = 0;
// The Phi value from the loop body typically is defined in the loop, but
// not always. So, we need to check if the value is defined in the loop.
unsigned PhiOp2 = LoopVal;
if (VRMap[LastStageNum].count(LoopVal))
PhiOp2 = VRMap[LastStageNum][LoopVal];
int StageScheduled = Schedule.getStage(&*BBI);
int LoopValStage = Schedule.getStage(MRI.getVRegDef(LoopVal));
unsigned NumStages = getStagesForReg(Def, CurStageNum);
if (NumStages == 0) {
// We don't need to generate a Phi anymore, but we need to rename any uses
// of the Phi value.
unsigned NewReg = VRMap[PrevStage][LoopVal];
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, 0, &*BBI, Def,
InitVal, NewReg);
if (VRMap[CurStageNum].count(LoopVal))
VRMap[CurStageNum][Def] = VRMap[CurStageNum][LoopVal];
}
// Adjust the number of Phis needed depending on the number of prologs left,
// and the distance from where the Phi is first scheduled. The number of
// Phis cannot exceed the number of prolog stages. Each stage can
// potentially define two values.
unsigned MaxPhis = PrologStage + 2;
if (!InKernel && (int)PrologStage <= LoopValStage)
MaxPhis = std::max((int)MaxPhis - (int)LoopValStage, 1);
unsigned NumPhis = std::min(NumStages, MaxPhis);
unsigned NewReg = 0;
unsigned AccessStage = (LoopValStage != -1) ? LoopValStage : StageScheduled;
// In the epilog, we may need to look back one stage to get the correct
// Phi name, because the epilog and prolog blocks execute the same stage.
// The correct name is from the previous block only when the Phi has
// been completely scheduled prior to the epilog, and Phi value is not
// needed in multiple stages.
int StageDiff = 0;
if (!InKernel && StageScheduled >= LoopValStage && AccessStage == 0 &&
NumPhis == 1)
StageDiff = 1;
// Adjust the computations below when the phi and the loop definition
// are scheduled in different stages.
if (InKernel && LoopValStage != -1 && StageScheduled > LoopValStage)
StageDiff = StageScheduled - LoopValStage;
for (unsigned np = 0; np < NumPhis; ++np) {
// If the Phi hasn't been scheduled, then use the initial Phi operand
// value. Otherwise, use the scheduled version of the instruction. This
// is a little complicated when a Phi references another Phi.
if (np > PrologStage || StageScheduled >= (int)LastStageNum)
PhiOp1 = InitVal;
// Check if the Phi has already been scheduled in a prolog stage.
else if (PrologStage >= AccessStage + StageDiff + np &&
VRMap[PrologStage - StageDiff - np].count(LoopVal) != 0)
PhiOp1 = VRMap[PrologStage - StageDiff - np][LoopVal];
// Check if the Phi has already been scheduled, but the loop instruction
// is either another Phi, or doesn't occur in the loop.
else if (PrologStage >= AccessStage + StageDiff + np) {
// If the Phi references another Phi, we need to examine the other
// Phi to get the correct value.
PhiOp1 = LoopVal;
MachineInstr *InstOp1 = MRI.getVRegDef(PhiOp1);
int Indirects = 1;
while (InstOp1 && InstOp1->isPHI() && InstOp1->getParent() == BB) {
int PhiStage = Schedule.getStage(InstOp1);
if ((int)(PrologStage - StageDiff - np) < PhiStage + Indirects)
PhiOp1 = getInitPhiReg(*InstOp1, BB);
else
PhiOp1 = getLoopPhiReg(*InstOp1, BB);
InstOp1 = MRI.getVRegDef(PhiOp1);
int PhiOpStage = Schedule.getStage(InstOp1);
int StageAdj = (PhiOpStage != -1 ? PhiStage - PhiOpStage : 0);
if (PhiOpStage != -1 && PrologStage - StageAdj >= Indirects + np &&
VRMap[PrologStage - StageAdj - Indirects - np].count(PhiOp1)) {
PhiOp1 = VRMap[PrologStage - StageAdj - Indirects - np][PhiOp1];
break;
}
++Indirects;
}
} else
PhiOp1 = InitVal;
// If this references a generated Phi in the kernel, get the Phi operand
// from the incoming block.
if (MachineInstr *InstOp1 = MRI.getVRegDef(PhiOp1))
if (InstOp1->isPHI() && InstOp1->getParent() == KernelBB)
PhiOp1 = getInitPhiReg(*InstOp1, KernelBB);
MachineInstr *PhiInst = MRI.getVRegDef(LoopVal);
bool LoopDefIsPhi = PhiInst && PhiInst->isPHI();
// In the epilog, a map lookup is needed to get the value from the kernel,
// or previous epilog block. How is does this depends on if the
// instruction is scheduled in the previous block.
if (!InKernel) {
int StageDiffAdj = 0;
if (LoopValStage != -1 && StageScheduled > LoopValStage)
StageDiffAdj = StageScheduled - LoopValStage;
// Use the loop value defined in the kernel, unless the kernel
// contains the last definition of the Phi.
if (np == 0 && PrevStage == LastStageNum &&
(StageScheduled != 0 || LoopValStage != 0) &&
VRMap[PrevStage - StageDiffAdj].count(LoopVal))
PhiOp2 = VRMap[PrevStage - StageDiffAdj][LoopVal];
// Use the value defined by the Phi. We add one because we switch
// from looking at the loop value to the Phi definition.
else if (np > 0 && PrevStage == LastStageNum &&
VRMap[PrevStage - np + 1].count(Def))
PhiOp2 = VRMap[PrevStage - np + 1][Def];
// Use the loop value defined in the kernel.
else if (static_cast<unsigned>(LoopValStage) > PrologStage + 1 &&
VRMap[PrevStage - StageDiffAdj - np].count(LoopVal))
PhiOp2 = VRMap[PrevStage - StageDiffAdj - np][LoopVal];
// Use the value defined by the Phi, unless we're generating the first
// epilog and the Phi refers to a Phi in a different stage.
else if (VRMap[PrevStage - np].count(Def) &&
(!LoopDefIsPhi || (PrevStage != LastStageNum) ||
(LoopValStage == StageScheduled)))
PhiOp2 = VRMap[PrevStage - np][Def];
}
// Check if we can reuse an existing Phi. This occurs when a Phi
// references another Phi, and the other Phi is scheduled in an
// earlier stage. We can try to reuse an existing Phi up until the last
// stage of the current Phi.
if (LoopDefIsPhi) {
if (static_cast<int>(PrologStage - np) >= StageScheduled) {
int LVNumStages = getStagesForPhi(LoopVal);
int StageDiff = (StageScheduled - LoopValStage);
LVNumStages -= StageDiff;
// Make sure the loop value Phi has been processed already.
if (LVNumStages > (int)np && VRMap[CurStageNum].count(LoopVal)) {
NewReg = PhiOp2;
unsigned ReuseStage = CurStageNum;
if (isLoopCarried(*PhiInst))
ReuseStage -= LVNumStages;
// Check if the Phi to reuse has been generated yet. If not, then
// there is nothing to reuse.
if (VRMap[ReuseStage - np].count(LoopVal)) {
NewReg = VRMap[ReuseStage - np][LoopVal];
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, np, &*BBI,
Def, NewReg);
// Update the map with the new Phi name.
VRMap[CurStageNum - np][Def] = NewReg;
PhiOp2 = NewReg;
if (VRMap[LastStageNum - np - 1].count(LoopVal))
PhiOp2 = VRMap[LastStageNum - np - 1][LoopVal];
if (IsLast && np == NumPhis - 1)
replaceRegUsesAfterLoop(Def, NewReg, BB, MRI, LIS);
continue;
}
}
}
if (InKernel && StageDiff > 0 &&
VRMap[CurStageNum - StageDiff - np].count(LoopVal))
PhiOp2 = VRMap[CurStageNum - StageDiff - np][LoopVal];
}
const TargetRegisterClass *RC = MRI.getRegClass(Def);
NewReg = MRI.createVirtualRegister(RC);
MachineInstrBuilder NewPhi =
BuildMI(*NewBB, NewBB->getFirstNonPHI(), DebugLoc(),
TII->get(TargetOpcode::PHI), NewReg);
NewPhi.addReg(PhiOp1).addMBB(BB1);
NewPhi.addReg(PhiOp2).addMBB(BB2);
if (np == 0)
InstrMap[NewPhi] = &*BBI;
// We define the Phis after creating the new pipelined code, so
// we need to rename the Phi values in scheduled instructions.
unsigned PrevReg = 0;
if (InKernel && VRMap[PrevStage - np].count(LoopVal))
PrevReg = VRMap[PrevStage - np][LoopVal];
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, np, &*BBI, Def,
NewReg, PrevReg);
// If the Phi has been scheduled, use the new name for rewriting.
if (VRMap[CurStageNum - np].count(Def)) {
unsigned R = VRMap[CurStageNum - np][Def];
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, np, &*BBI, R,
NewReg);
}
// Check if we need to rename any uses that occurs after the loop. The
// register to replace depends on whether the Phi is scheduled in the
// epilog.
if (IsLast && np == NumPhis - 1)
replaceRegUsesAfterLoop(Def, NewReg, BB, MRI, LIS);
// In the kernel, a dependent Phi uses the value from this Phi.
if (InKernel)
PhiOp2 = NewReg;
// Update the map with the new Phi name.
VRMap[CurStageNum - np][Def] = NewReg;
}
while (NumPhis++ < NumStages) {
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, NumPhis, &*BBI, Def,
NewReg, 0);
}
// Check if we need to rename a Phi that has been eliminated due to
// scheduling.
if (NumStages == 0 && IsLast && VRMap[CurStageNum].count(LoopVal))
replaceRegUsesAfterLoop(Def, VRMap[CurStageNum][LoopVal], BB, MRI, LIS);
}
}
/// Generate Phis for the specified block in the generated pipelined code.
/// These are new Phis needed because the definition is scheduled after the
/// use in the pipelined sequence.
void ModuloScheduleExpander::generatePhis(
MachineBasicBlock *NewBB, MachineBasicBlock *BB1, MachineBasicBlock *BB2,
MachineBasicBlock *KernelBB, ValueMapTy *VRMap, InstrMapTy &InstrMap,
unsigned LastStageNum, unsigned CurStageNum, bool IsLast) {
// Compute the stage number that contains the initial Phi value, and
// the Phi from the previous stage.
unsigned PrologStage = 0;
unsigned PrevStage = 0;
unsigned StageDiff = CurStageNum - LastStageNum;
bool InKernel = (StageDiff == 0);
if (InKernel) {
PrologStage = LastStageNum - 1;
PrevStage = CurStageNum;
} else {
PrologStage = LastStageNum - StageDiff;
PrevStage = LastStageNum + StageDiff - 1;
}
for (MachineBasicBlock::iterator BBI = BB->getFirstNonPHI(),
BBE = BB->instr_end();
BBI != BBE; ++BBI) {
for (unsigned i = 0, e = BBI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = BBI->getOperand(i);
if (!MO.isReg() || !MO.isDef() ||
!Register::isVirtualRegister(MO.getReg()))
continue;
int StageScheduled = Schedule.getStage(&*BBI);
assert(StageScheduled != -1 && "Expecting scheduled instruction.");
Register Def = MO.getReg();
unsigned NumPhis = getStagesForReg(Def, CurStageNum);
// An instruction scheduled in stage 0 and is used after the loop
// requires a phi in the epilog for the last definition from either
// the kernel or prolog.
if (!InKernel && NumPhis == 0 && StageScheduled == 0 &&
hasUseAfterLoop(Def, BB, MRI))
NumPhis = 1;
if (!InKernel && (unsigned)StageScheduled > PrologStage)
continue;
unsigned PhiOp2 = VRMap[PrevStage][Def];
if (MachineInstr *InstOp2 = MRI.getVRegDef(PhiOp2))
if (InstOp2->isPHI() && InstOp2->getParent() == NewBB)
PhiOp2 = getLoopPhiReg(*InstOp2, BB2);
// The number of Phis can't exceed the number of prolog stages. The
// prolog stage number is zero based.
if (NumPhis > PrologStage + 1 - StageScheduled)
NumPhis = PrologStage + 1 - StageScheduled;
for (unsigned np = 0; np < NumPhis; ++np) {
unsigned PhiOp1 = VRMap[PrologStage][Def];
if (np <= PrologStage)
PhiOp1 = VRMap[PrologStage - np][Def];
if (MachineInstr *InstOp1 = MRI.getVRegDef(PhiOp1)) {
if (InstOp1->isPHI() && InstOp1->getParent() == KernelBB)
PhiOp1 = getInitPhiReg(*InstOp1, KernelBB);
if (InstOp1->isPHI() && InstOp1->getParent() == NewBB)
PhiOp1 = getInitPhiReg(*InstOp1, NewBB);
}
if (!InKernel)
PhiOp2 = VRMap[PrevStage - np][Def];
const TargetRegisterClass *RC = MRI.getRegClass(Def);
Register NewReg = MRI.createVirtualRegister(RC);
MachineInstrBuilder NewPhi =
BuildMI(*NewBB, NewBB->getFirstNonPHI(), DebugLoc(),
TII->get(TargetOpcode::PHI), NewReg);
NewPhi.addReg(PhiOp1).addMBB(BB1);
NewPhi.addReg(PhiOp2).addMBB(BB2);
if (np == 0)
InstrMap[NewPhi] = &*BBI;
// Rewrite uses and update the map. The actions depend upon whether
// we generating code for the kernel or epilog blocks.
if (InKernel) {
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, np, &*BBI, PhiOp1,
NewReg);
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, np, &*BBI, PhiOp2,
NewReg);
PhiOp2 = NewReg;
VRMap[PrevStage - np - 1][Def] = NewReg;
} else {
VRMap[CurStageNum - np][Def] = NewReg;
if (np == NumPhis - 1)
rewriteScheduledInstr(NewBB, InstrMap, CurStageNum, np, &*BBI, Def,
NewReg);
}
if (IsLast && np == NumPhis - 1)
replaceRegUsesAfterLoop(Def, NewReg, BB, MRI, LIS);
}
}
}
}
/// Remove instructions that generate values with no uses.
/// Typically, these are induction variable operations that generate values
/// used in the loop itself. A dead instruction has a definition with
/// no uses, or uses that occur in the original loop only.
void ModuloScheduleExpander::removeDeadInstructions(MachineBasicBlock *KernelBB,
MBBVectorTy &EpilogBBs) {
// For each epilog block, check that the value defined by each instruction
// is used. If not, delete it.
for (MachineBasicBlock *MBB : llvm::reverse(EpilogBBs))
for (MachineBasicBlock::reverse_instr_iterator MI = MBB->instr_rbegin(),
ME = MBB->instr_rend();
MI != ME;) {
// From DeadMachineInstructionElem. Don't delete inline assembly.
if (MI->isInlineAsm()) {
++MI;
continue;
}
bool SawStore = false;
// Check if it's safe to remove the instruction due to side effects.
// We can, and want to, remove Phis here.
if (!MI->isSafeToMove(nullptr, SawStore) && !MI->isPHI()) {
++MI;
continue;
}
bool used = true;
for (const MachineOperand &MO : MI->operands()) {
if (!MO.isReg() || !MO.isDef())
continue;
Register reg = MO.getReg();
// Assume physical registers are used, unless they are marked dead.
if (Register::isPhysicalRegister(reg)) {
used = !MO.isDead();
if (used)
break;
continue;
}
unsigned realUses = 0;
for (const MachineOperand &U : MRI.use_operands(reg)) {
// Check if there are any uses that occur only in the original
// loop. If so, that's not a real use.
if (U.getParent()->getParent() != BB) {
realUses++;
used = true;
break;
}
}
if (realUses > 0)
break;
used = false;
}
if (!used) {
LIS.RemoveMachineInstrFromMaps(*MI);
MI++->eraseFromParent();
continue;
}
++MI;
}
// In the kernel block, check if we can remove a Phi that generates a value
// used in an instruction removed in the epilog block.
for (MachineInstr &MI : llvm::make_early_inc_range(KernelBB->phis())) {
Register reg = MI.getOperand(0).getReg();
if (MRI.use_begin(reg) == MRI.use_end()) {
LIS.RemoveMachineInstrFromMaps(MI);
MI.eraseFromParent();
}
}
}
/// For loop carried definitions, we split the lifetime of a virtual register
/// that has uses past the definition in the next iteration. A copy with a new
/// virtual register is inserted before the definition, which helps with
/// generating a better register assignment.
///
/// v1 = phi(a, v2) v1 = phi(a, v2)
/// v2 = phi(b, v3) v2 = phi(b, v3)
/// v3 = .. v4 = copy v1
/// .. = V1 v3 = ..
/// .. = v4
void ModuloScheduleExpander::splitLifetimes(MachineBasicBlock *KernelBB,
MBBVectorTy &EpilogBBs) {
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
for (auto &PHI : KernelBB->phis()) {
Register Def = PHI.getOperand(0).getReg();
// Check for any Phi definition that used as an operand of another Phi
// in the same block.
for (MachineRegisterInfo::use_instr_iterator I = MRI.use_instr_begin(Def),
E = MRI.use_instr_end();
I != E; ++I) {
if (I->isPHI() && I->getParent() == KernelBB) {
// Get the loop carried definition.
unsigned LCDef = getLoopPhiReg(PHI, KernelBB);
if (!LCDef)
continue;
MachineInstr *MI = MRI.getVRegDef(LCDef);
if (!MI || MI->getParent() != KernelBB || MI->isPHI())
continue;
// Search through the rest of the block looking for uses of the Phi
// definition. If one occurs, then split the lifetime.
unsigned SplitReg = 0;
for (auto &BBJ : make_range(MachineBasicBlock::instr_iterator(MI),
KernelBB->instr_end()))
if (BBJ.readsRegister(Def)) {
// We split the lifetime when we find the first use.
if (SplitReg == 0) {
SplitReg = MRI.createVirtualRegister(MRI.getRegClass(Def));
BuildMI(*KernelBB, MI, MI->getDebugLoc(),
TII->get(TargetOpcode::COPY), SplitReg)
.addReg(Def);
}
BBJ.substituteRegister(Def, SplitReg, 0, *TRI);
}
if (!SplitReg)
continue;
// Search through each of the epilog blocks for any uses to be renamed.
for (auto &Epilog : EpilogBBs)
for (auto &I : *Epilog)
if (I.readsRegister(Def))
I.substituteRegister(Def, SplitReg, 0, *TRI);
break;
}
}
}
}
/// Remove the incoming block from the Phis in a basic block.
static void removePhis(MachineBasicBlock *BB, MachineBasicBlock *Incoming) {
for (MachineInstr &MI : *BB) {
if (!MI.isPHI())
break;
for (unsigned i = 1, e = MI.getNumOperands(); i != e; i += 2)
if (MI.getOperand(i + 1).getMBB() == Incoming) {
MI.removeOperand(i + 1);
MI.removeOperand(i);
break;
}
}
}
/// Create branches from each prolog basic block to the appropriate epilog
/// block. These edges are needed if the loop ends before reaching the
/// kernel.
void ModuloScheduleExpander::addBranches(MachineBasicBlock &PreheaderBB,
MBBVectorTy &PrologBBs,
MachineBasicBlock *KernelBB,
MBBVectorTy &EpilogBBs,
ValueMapTy *VRMap) {
assert(PrologBBs.size() == EpilogBBs.size() && "Prolog/Epilog mismatch");
MachineBasicBlock *LastPro = KernelBB;
MachineBasicBlock *LastEpi = KernelBB;
// Start from the blocks connected to the kernel and work "out"
// to the first prolog and the last epilog blocks.
SmallVector<MachineInstr *, 4> PrevInsts;
unsigned MaxIter = PrologBBs.size() - 1;
for (unsigned i = 0, j = MaxIter; i <= MaxIter; ++i, --j) {
// Add branches to the prolog that go to the corresponding
// epilog, and the fall-thru prolog/kernel block.
MachineBasicBlock *Prolog = PrologBBs[j];
MachineBasicBlock *Epilog = EpilogBBs[i];
SmallVector<MachineOperand, 4> Cond;
Optional<bool> StaticallyGreater =
LoopInfo->createTripCountGreaterCondition(j + 1, *Prolog, Cond);
unsigned numAdded = 0;
if (!StaticallyGreater.hasValue()) {
Prolog->addSuccessor(Epilog);
numAdded = TII->insertBranch(*Prolog, Epilog, LastPro, Cond, DebugLoc());
} else if (*StaticallyGreater == false) {
Prolog->addSuccessor(Epilog);
Prolog->removeSuccessor(LastPro);
LastEpi->removeSuccessor(Epilog);
numAdded = TII->insertBranch(*Prolog, Epilog, nullptr, Cond, DebugLoc());
removePhis(Epilog, LastEpi);
// Remove the blocks that are no longer referenced.
if (LastPro != LastEpi) {
LastEpi->clear();
LastEpi->eraseFromParent();
}
if (LastPro == KernelBB) {
LoopInfo->disposed();
NewKernel = nullptr;
}
LastPro->clear();
LastPro->eraseFromParent();
} else {
numAdded = TII->insertBranch(*Prolog, LastPro, nullptr, Cond, DebugLoc());
removePhis(Epilog, Prolog);
}
LastPro = Prolog;
LastEpi = Epilog;
for (MachineBasicBlock::reverse_instr_iterator I = Prolog->instr_rbegin(),
E = Prolog->instr_rend();
I != E && numAdded > 0; ++I, --numAdded)
updateInstruction(&*I, false, j, 0, VRMap);
}
if (NewKernel) {
LoopInfo->setPreheader(PrologBBs[MaxIter]);
LoopInfo->adjustTripCount(-(MaxIter + 1));
}
}
/// Return true if we can compute the amount the instruction changes
/// during each iteration. Set Delta to the amount of the change.
bool ModuloScheduleExpander::computeDelta(MachineInstr &MI, unsigned &Delta) {
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
const MachineOperand *BaseOp;
int64_t Offset;
bool OffsetIsScalable;
if (!TII->getMemOperandWithOffset(MI, BaseOp, Offset, OffsetIsScalable, TRI))
return false;
// FIXME: This algorithm assumes instructions have fixed-size offsets.
if (OffsetIsScalable)
return false;
if (!BaseOp->isReg())
return false;
Register BaseReg = BaseOp->getReg();
MachineRegisterInfo &MRI = MF.getRegInfo();
// Check if there is a Phi. If so, get the definition in the loop.
MachineInstr *BaseDef = MRI.getVRegDef(BaseReg);
if (BaseDef && BaseDef->isPHI()) {
BaseReg = getLoopPhiReg(*BaseDef, MI.getParent());
BaseDef = MRI.getVRegDef(BaseReg);
}
if (!BaseDef)
return false;
int D = 0;
if (!TII->getIncrementValue(*BaseDef, D) && D >= 0)
return false;
Delta = D;
return true;
}
/// Update the memory operand with a new offset when the pipeliner
/// generates a new copy of the instruction that refers to a
/// different memory location.
void ModuloScheduleExpander::updateMemOperands(MachineInstr &NewMI,
MachineInstr &OldMI,
unsigned Num) {
if (Num == 0)
return;
// If the instruction has memory operands, then adjust the offset
// when the instruction appears in different stages.
if (NewMI.memoperands_empty())
return;
SmallVector<MachineMemOperand *, 2> NewMMOs;
for (MachineMemOperand *MMO : NewMI.memoperands()) {
// TODO: Figure out whether isAtomic is really necessary (see D57601).
if (MMO->isVolatile() || MMO->isAtomic() ||
(MMO->isInvariant() && MMO->isDereferenceable()) ||
(!MMO->getValue())) {
NewMMOs.push_back(MMO);
continue;
}
unsigned Delta;
if (Num != UINT_MAX && computeDelta(OldMI, Delta)) {
int64_t AdjOffset = Delta * Num;
NewMMOs.push_back(
MF.getMachineMemOperand(MMO, AdjOffset, MMO->getSize()));
} else {
NewMMOs.push_back(
MF.getMachineMemOperand(MMO, 0, MemoryLocation::UnknownSize));
}
}
NewMI.setMemRefs(MF, NewMMOs);
}
/// Clone the instruction for the new pipelined loop and update the
/// memory operands, if needed.
MachineInstr *ModuloScheduleExpander::cloneInstr(MachineInstr *OldMI,
unsigned CurStageNum,
unsigned InstStageNum) {
MachineInstr *NewMI = MF.CloneMachineInstr(OldMI);
// Check for tied operands in inline asm instructions. This should be handled
// elsewhere, but I'm not sure of the best solution.
if (OldMI->isInlineAsm())
for (unsigned i = 0, e = OldMI->getNumOperands(); i != e; ++i) {
const auto &MO = OldMI->getOperand(i);
if (MO.isReg() && MO.isUse())
break;
unsigned UseIdx;
if (OldMI->isRegTiedToUseOperand(i, &UseIdx))
NewMI->tieOperands(i, UseIdx);
}
updateMemOperands(*NewMI, *OldMI, CurStageNum - InstStageNum);
return NewMI;
}
/// Clone the instruction for the new pipelined loop. If needed, this
/// function updates the instruction using the values saved in the
/// InstrChanges structure.
MachineInstr *ModuloScheduleExpander::cloneAndChangeInstr(
MachineInstr *OldMI, unsigned CurStageNum, unsigned InstStageNum) {
MachineInstr *NewMI = MF.CloneMachineInstr(OldMI);
auto It = InstrChanges.find(OldMI);
if (It != InstrChanges.end()) {
std::pair<unsigned, int64_t> RegAndOffset = It->second;
unsigned BasePos, OffsetPos;
if (!TII->getBaseAndOffsetPosition(*OldMI, BasePos, OffsetPos))
return nullptr;
int64_t NewOffset = OldMI->getOperand(OffsetPos).getImm();
MachineInstr *LoopDef = findDefInLoop(RegAndOffset.first);
if (Schedule.getStage(LoopDef) > (signed)InstStageNum)
NewOffset += RegAndOffset.second * (CurStageNum - InstStageNum);
NewMI->getOperand(OffsetPos).setImm(NewOffset);
}
updateMemOperands(*NewMI, *OldMI, CurStageNum - InstStageNum);
return NewMI;
}
/// Update the machine instruction with new virtual registers. This
/// function may change the defintions and/or uses.
void ModuloScheduleExpander::updateInstruction(MachineInstr *NewMI,
bool LastDef,
unsigned CurStageNum,
unsigned InstrStageNum,
ValueMapTy *VRMap) {
for (MachineOperand &MO : NewMI->operands()) {
if (!MO.isReg() || !Register::isVirtualRegister(MO.getReg()))
continue;
Register reg = MO.getReg();
if (MO.isDef()) {
// Create a new virtual register for the definition.
const TargetRegisterClass *RC = MRI.getRegClass(reg);
Register NewReg = MRI.createVirtualRegister(RC);
MO.setReg(NewReg);
VRMap[CurStageNum][reg] = NewReg;
if (LastDef)
replaceRegUsesAfterLoop(reg, NewReg, BB, MRI, LIS);
} else if (MO.isUse()) {
MachineInstr *Def = MRI.getVRegDef(reg);
// Compute the stage that contains the last definition for instruction.
int DefStageNum = Schedule.getStage(Def);
unsigned StageNum = CurStageNum;
if (DefStageNum != -1 && (int)InstrStageNum > DefStageNum) {
// Compute the difference in stages between the defintion and the use.
unsigned StageDiff = (InstrStageNum - DefStageNum);
// Make an adjustment to get the last definition.
StageNum -= StageDiff;
}
if (VRMap[StageNum].count(reg))
MO.setReg(VRMap[StageNum][reg]);
}
}
}
/// Return the instruction in the loop that defines the register.
/// If the definition is a Phi, then follow the Phi operand to
/// the instruction in the loop.
MachineInstr *ModuloScheduleExpander::findDefInLoop(unsigned Reg) {
SmallPtrSet<MachineInstr *, 8> Visited;
MachineInstr *Def = MRI.getVRegDef(Reg);
while (Def->isPHI()) {
if (!Visited.insert(Def).second)
break;
for (unsigned i = 1, e = Def->getNumOperands(); i < e; i += 2)
if (Def->getOperand(i + 1).getMBB() == BB) {
Def = MRI.getVRegDef(Def->getOperand(i).getReg());
break;
}
}
return Def;
}
/// Return the new name for the value from the previous stage.
unsigned ModuloScheduleExpander::getPrevMapVal(
unsigned StageNum, unsigned PhiStage, unsigned LoopVal, unsigned LoopStage,
ValueMapTy *VRMap, MachineBasicBlock *BB) {
unsigned PrevVal = 0;
if (StageNum > PhiStage) {
MachineInstr *LoopInst = MRI.getVRegDef(LoopVal);
if (PhiStage == LoopStage && VRMap[StageNum - 1].count(LoopVal))
// The name is defined in the previous stage.
PrevVal = VRMap[StageNum - 1][LoopVal];
else if (VRMap[StageNum].count(LoopVal))
// The previous name is defined in the current stage when the instruction
// order is swapped.
PrevVal = VRMap[StageNum][LoopVal];
else if (!LoopInst->isPHI() || LoopInst->getParent() != BB)
// The loop value hasn't yet been scheduled.
PrevVal = LoopVal;
else if (StageNum == PhiStage + 1)
// The loop value is another phi, which has not been scheduled.
PrevVal = getInitPhiReg(*LoopInst, BB);
else if (StageNum > PhiStage + 1 && LoopInst->getParent() == BB)
// The loop value is another phi, which has been scheduled.
PrevVal =
getPrevMapVal(StageNum - 1, PhiStage, getLoopPhiReg(*LoopInst, BB),
LoopStage, VRMap, BB);
}
return PrevVal;
}
/// Rewrite the Phi values in the specified block to use the mappings
/// from the initial operand. Once the Phi is scheduled, we switch
/// to using the loop value instead of the Phi value, so those names
/// do not need to be rewritten.
void ModuloScheduleExpander::rewritePhiValues(MachineBasicBlock *NewBB,
unsigned StageNum,
ValueMapTy *VRMap,
InstrMapTy &InstrMap) {
for (auto &PHI : BB->phis()) {
unsigned InitVal = 0;
unsigned LoopVal = 0;
getPhiRegs(PHI, BB, InitVal, LoopVal);
Register PhiDef = PHI.getOperand(0).getReg();
unsigned PhiStage = (unsigned)Schedule.getStage(MRI.getVRegDef(PhiDef));
unsigned LoopStage = (unsigned)Schedule.getStage(MRI.getVRegDef(LoopVal));
unsigned NumPhis = getStagesForPhi(PhiDef);
if (NumPhis > StageNum)
NumPhis = StageNum;
for (unsigned np = 0; np <= NumPhis; ++np) {
unsigned NewVal =
getPrevMapVal(StageNum - np, PhiStage, LoopVal, LoopStage, VRMap, BB);
if (!NewVal)
NewVal = InitVal;
rewriteScheduledInstr(NewBB, InstrMap, StageNum - np, np, &PHI, PhiDef,
NewVal);
}
}
}
/// Rewrite a previously scheduled instruction to use the register value
/// from the new instruction. Make sure the instruction occurs in the
/// basic block, and we don't change the uses in the new instruction.
void ModuloScheduleExpander::rewriteScheduledInstr(
MachineBasicBlock *BB, InstrMapTy &InstrMap, unsigned CurStageNum,
unsigned PhiNum, MachineInstr *Phi, unsigned OldReg, unsigned NewReg,
unsigned PrevReg) {
bool InProlog = (CurStageNum < (unsigned)Schedule.getNumStages() - 1);
int StagePhi = Schedule.getStage(Phi) + PhiNum;
// Rewrite uses that have been scheduled already to use the new
// Phi register.
for (MachineOperand &UseOp :
llvm::make_early_inc_range(MRI.use_operands(OldReg))) {
MachineInstr *UseMI = UseOp.getParent();
if (UseMI->getParent() != BB)
continue;
if (UseMI->isPHI()) {
if (!Phi->isPHI() && UseMI->getOperand(0).getReg() == NewReg)
continue;
if (getLoopPhiReg(*UseMI, BB) != OldReg)
continue;
}
InstrMapTy::iterator OrigInstr = InstrMap.find(UseMI);
assert(OrigInstr != InstrMap.end() && "Instruction not scheduled.");
MachineInstr *OrigMI = OrigInstr->second;
int StageSched = Schedule.getStage(OrigMI);
int CycleSched = Schedule.getCycle(OrigMI);
unsigned ReplaceReg = 0;
// This is the stage for the scheduled instruction.
if (StagePhi == StageSched && Phi->isPHI()) {
int CyclePhi = Schedule.getCycle(Phi);
if (PrevReg && InProlog)
ReplaceReg = PrevReg;
else if (PrevReg && !isLoopCarried(*Phi) &&
(CyclePhi <= CycleSched || OrigMI->isPHI()))
ReplaceReg = PrevReg;
else
ReplaceReg = NewReg;
}
// The scheduled instruction occurs before the scheduled Phi, and the
// Phi is not loop carried.
if (!InProlog && StagePhi + 1 == StageSched && !isLoopCarried(*Phi))
ReplaceReg = NewReg;
if (StagePhi > StageSched && Phi->isPHI())
ReplaceReg = NewReg;
if (!InProlog && !Phi->isPHI() && StagePhi < StageSched)
ReplaceReg = NewReg;
if (ReplaceReg) {
MRI.constrainRegClass(ReplaceReg, MRI.getRegClass(OldReg));
UseOp.setReg(ReplaceReg);
}
}
}
bool ModuloScheduleExpander::isLoopCarried(MachineInstr &Phi) {
if (!Phi.isPHI())
return false;
int DefCycle = Schedule.getCycle(&Phi);
int DefStage = Schedule.getStage(&Phi);
unsigned InitVal = 0;
unsigned LoopVal = 0;
getPhiRegs(Phi, Phi.getParent(), InitVal, LoopVal);
MachineInstr *Use = MRI.getVRegDef(LoopVal);
if (!Use || Use->isPHI())
return true;
int LoopCycle = Schedule.getCycle(Use);
int LoopStage = Schedule.getStage(Use);
return (LoopCycle > DefCycle) || (LoopStage <= DefStage);
}
//===----------------------------------------------------------------------===//
// PeelingModuloScheduleExpander implementation
//===----------------------------------------------------------------------===//
// This is a reimplementation of ModuloScheduleExpander that works by creating
// a fully correct steady-state kernel and peeling off the prolog and epilogs.
//===----------------------------------------------------------------------===//
namespace {
// Remove any dead phis in MBB. Dead phis either have only one block as input
// (in which case they are the identity) or have no uses.
void EliminateDeadPhis(MachineBasicBlock *MBB, MachineRegisterInfo &MRI,
LiveIntervals *LIS, bool KeepSingleSrcPhi = false) {
bool Changed = true;
while (Changed) {
Changed = false;
for (MachineInstr &MI : llvm::make_early_inc_range(MBB->phis())) {
assert(MI.isPHI());
if (MRI.use_empty(MI.getOperand(0).getReg())) {
if (LIS)
LIS->RemoveMachineInstrFromMaps(MI);
MI.eraseFromParent();
Changed = true;
} else if (!KeepSingleSrcPhi && MI.getNumExplicitOperands() == 3) {
MRI.constrainRegClass(MI.getOperand(1).getReg(),
MRI.getRegClass(MI.getOperand(0).getReg()));
MRI.replaceRegWith(MI.getOperand(0).getReg(),
MI.getOperand(1).getReg());
if (LIS)
LIS->RemoveMachineInstrFromMaps(MI);
MI.eraseFromParent();
Changed = true;
}
}
}
}
/// Rewrites the kernel block in-place to adhere to the given schedule.
/// KernelRewriter holds all of the state required to perform the rewriting.
class KernelRewriter {
ModuloSchedule &S;
MachineBasicBlock *BB;
MachineBasicBlock *PreheaderBB, *ExitBB;
MachineRegisterInfo &MRI;
const TargetInstrInfo *TII;
LiveIntervals *LIS;
// Map from register class to canonical undef register for that class.
DenseMap<const TargetRegisterClass *, Register> Undefs;
// Map from <LoopReg, InitReg> to phi register for all created phis. Note that
// this map is only used when InitReg is non-undef.
DenseMap<std::pair<unsigned, unsigned>, Register> Phis;
// Map from LoopReg to phi register where the InitReg is undef.
DenseMap<Register, Register> UndefPhis;
// Reg is used by MI. Return the new register MI should use to adhere to the
// schedule. Insert phis as necessary.
Register remapUse(Register Reg, MachineInstr &MI);
// Insert a phi that carries LoopReg from the loop body and InitReg otherwise.
// If InitReg is not given it is chosen arbitrarily. It will either be undef
// or will be chosen so as to share another phi.
Register phi(Register LoopReg, Optional<Register> InitReg = {},
const TargetRegisterClass *RC = nullptr);
// Create an undef register of the given register class.
Register undef(const TargetRegisterClass *RC);
public:
KernelRewriter(MachineLoop &L, ModuloSchedule &S, MachineBasicBlock *LoopBB,
LiveIntervals *LIS = nullptr);
void rewrite();
};
} // namespace
KernelRewriter::KernelRewriter(MachineLoop &L, ModuloSchedule &S,
MachineBasicBlock *LoopBB, LiveIntervals *LIS)
: S(S), BB(LoopBB), PreheaderBB(L.getLoopPreheader()),
ExitBB(L.getExitBlock()), MRI(BB->getParent()->getRegInfo()),
TII(BB->getParent()->getSubtarget().getInstrInfo()), LIS(LIS) {
PreheaderBB = *BB->pred_begin();
if (PreheaderBB == BB)
PreheaderBB = *std::next(BB->pred_begin());
}
void KernelRewriter::rewrite() {
// Rearrange the loop to be in schedule order. Note that the schedule may
// contain instructions that are not owned by the loop block (InstrChanges and
// friends), so we gracefully handle unowned instructions and delete any
// instructions that weren't in the schedule.
auto InsertPt = BB->getFirstTerminator();
MachineInstr *FirstMI = nullptr;
for (MachineInstr *MI : S.getInstructions()) {
if (MI->isPHI())
continue;
if (MI->getParent())
MI->removeFromParent();
BB->insert(InsertPt, MI);
if (!FirstMI)
FirstMI = MI;
}
assert(FirstMI && "Failed to find first MI in schedule");
// At this point all of the scheduled instructions are between FirstMI
// and the end of the block. Kill from the first non-phi to FirstMI.
for (auto I = BB->getFirstNonPHI(); I != FirstMI->getIterator();) {
if (LIS)
LIS->RemoveMachineInstrFromMaps(*I);
(I++)->eraseFromParent();
}
// Now remap every instruction in the loop.
for (MachineInstr &MI : *BB) {
if (MI.isPHI() || MI.isTerminator())
continue;
for (MachineOperand &MO : MI.uses()) {
if (!MO.isReg() || MO.getReg().isPhysical() || MO.isImplicit())
continue;
Register Reg = remapUse(MO.getReg(), MI);
MO.setReg(Reg);
}
}
EliminateDeadPhis(BB, MRI, LIS);
// Ensure a phi exists for all instructions that are either referenced by
// an illegal phi or by an instruction outside the loop. This allows us to
// treat remaps of these values the same as "normal" values that come from
// loop-carried phis.
for (auto MI = BB->getFirstNonPHI(); MI != BB->end(); ++MI) {
if (MI->isPHI()) {
Register R = MI->getOperand(0).getReg();
phi(R);
continue;
}
for (MachineOperand &Def : MI->defs()) {
for (MachineInstr &MI : MRI.use_instructions(Def.getReg())) {
if (MI.getParent() != BB) {
phi(Def.getReg());
break;
}
}
}
}
}
Register KernelRewriter::remapUse(Register Reg, MachineInstr &MI) {
MachineInstr *Producer = MRI.getUniqueVRegDef(Reg);
if (!Producer)
return Reg;
int ConsumerStage = S.getStage(&MI);
if (!Producer->isPHI()) {
// Non-phi producers are simple to remap. Insert as many phis as the
// difference between the consumer and producer stages.
if (Producer->getParent() != BB)
// Producer was not inside the loop. Use the register as-is.
return Reg;
int ProducerStage = S.getStage(Producer);
assert(ConsumerStage != -1 &&
"In-loop consumer should always be scheduled!");
assert(ConsumerStage >= ProducerStage);
unsigned StageDiff = ConsumerStage - ProducerStage;
for (unsigned I = 0; I < StageDiff; ++I)
Reg = phi(Reg);
return Reg;
}
// First, dive through the phi chain to find the defaults for the generated
// phis.
SmallVector<Optional<Register>, 4> Defaults;
Register LoopReg = Reg;
auto LoopProducer = Producer;
while (LoopProducer->isPHI() && LoopProducer->getParent() == BB) {
LoopReg = getLoopPhiReg(*LoopProducer, BB);
Defaults.emplace_back(getInitPhiReg(*LoopProducer, BB));
LoopProducer = MRI.getUniqueVRegDef(LoopReg);
assert(LoopProducer);
}
int LoopProducerStage = S.getStage(LoopProducer);
Optional<Register> IllegalPhiDefault;
if (LoopProducerStage == -1) {
// Do nothing.
} else if (LoopProducerStage > ConsumerStage) {
// This schedule is only representable if ProducerStage == ConsumerStage+1.
// In addition, Consumer's cycle must be scheduled after Producer in the
// rescheduled loop. This is enforced by the pipeliner's ASAP and ALAP
// functions.
#ifndef NDEBUG // Silence unused variables in non-asserts mode.
int LoopProducerCycle = S.getCycle(LoopProducer);
int ConsumerCycle = S.getCycle(&MI);
#endif
assert(LoopProducerCycle <= ConsumerCycle);
assert(LoopProducerStage == ConsumerStage + 1);
// Peel off the first phi from Defaults and insert a phi between producer
// and consumer. This phi will not be at the front of the block so we
// consider it illegal. It will only exist during the rewrite process; it
// needs to exist while we peel off prologs because these could take the
// default value. After that we can replace all uses with the loop producer
// value.
IllegalPhiDefault = Defaults.front();
Defaults.erase(Defaults.begin());
} else {
assert(ConsumerStage >= LoopProducerStage);
int StageDiff = ConsumerStage - LoopProducerStage;
if (StageDiff > 0) {
LLVM_DEBUG(dbgs() << " -- padding defaults array from " << Defaults.size()
<< " to " << (Defaults.size() + StageDiff) << "\n");
// If we need more phis than we have defaults for, pad out with undefs for
// the earliest phis, which are at the end of the defaults chain (the
// chain is in reverse order).
Defaults.resize(Defaults.size() + StageDiff, Defaults.empty()
? Optional<Register>()
: Defaults.back());
}
}
// Now we know the number of stages to jump back, insert the phi chain.
auto DefaultI = Defaults.rbegin();
while (DefaultI != Defaults.rend())
LoopReg = phi(LoopReg, *DefaultI++, MRI.getRegClass(Reg));
if (IllegalPhiDefault.hasValue()) {
// The consumer optionally consumes LoopProducer in the same iteration
// (because the producer is scheduled at an earlier cycle than the consumer)
// or the initial value. To facilitate this we create an illegal block here
// by embedding a phi in the middle of the block. We will fix this up
// immediately prior to pruning.
auto RC = MRI.getRegClass(Reg);
Register R = MRI.createVirtualRegister(RC);
MachineInstr *IllegalPhi =
BuildMI(*BB, MI, DebugLoc(), TII->get(TargetOpcode::PHI), R)
.addReg(IllegalPhiDefault.getValue())
.addMBB(PreheaderBB) // Block choice is arbitrary and has no effect.
.addReg(LoopReg)
.addMBB(BB); // Block choice is arbitrary and has no effect.
// Illegal phi should belong to the producer stage so that it can be
// filtered correctly during peeling.
S.setStage(IllegalPhi, LoopProducerStage);
return R;
}
return LoopReg;
}
Register KernelRewriter::phi(Register LoopReg, Optional<Register> InitReg,
const TargetRegisterClass *RC) {
// If the init register is not undef, try and find an existing phi.
if (InitReg.hasValue()) {
auto I = Phis.find({LoopReg, InitReg.getValue()});
if (I != Phis.end())
return I->second;
} else {
for (auto &KV : Phis) {
if (KV.first.first == LoopReg)
return KV.second;
}
}
// InitReg is either undef or no existing phi takes InitReg as input. Try and
// find a phi that takes undef as input.
auto I = UndefPhis.find(LoopReg);
if (I != UndefPhis.end()) {
Register R = I->second;
if (!InitReg.hasValue())
// Found a phi taking undef as input, and this input is undef so return
// without any more changes.
return R;
// Found a phi taking undef as input, so rewrite it to take InitReg.
MachineInstr *MI = MRI.getVRegDef(R);
MI->getOperand(1).setReg(InitReg.getValue());
Phis.insert({{LoopReg, InitReg.getValue()}, R});
MRI.constrainRegClass(R, MRI.getRegClass(InitReg.getValue()));
UndefPhis.erase(I);
return R;
}
// Failed to find any existing phi to reuse, so create a new one.
if (!RC)
RC = MRI.getRegClass(LoopReg);
Register R = MRI.createVirtualRegister(RC);
if (InitReg.hasValue())
MRI.constrainRegClass(R, MRI.getRegClass(*InitReg));
BuildMI(*BB, BB->getFirstNonPHI(), DebugLoc(), TII->get(TargetOpcode::PHI), R)
.addReg(InitReg.hasValue() ? *InitReg : undef(RC))
.addMBB(PreheaderBB)
.addReg(LoopReg)
.addMBB(BB);
if (!InitReg.hasValue())
UndefPhis[LoopReg] = R;
else
Phis[{LoopReg, *InitReg}] = R;
return R;
}
Register KernelRewriter::undef(const TargetRegisterClass *RC) {
Register &R = Undefs[RC];
if (R == 0) {
// Create an IMPLICIT_DEF that defines this register if we need it.
// All uses of this should be removed by the time we have finished unrolling
// prologs and epilogs.
R = MRI.createVirtualRegister(RC);
auto *InsertBB = &PreheaderBB->getParent()->front();
BuildMI(*InsertBB, InsertBB->getFirstTerminator(), DebugLoc(),
TII->get(TargetOpcode::IMPLICIT_DEF), R);
}
return R;
}
namespace {
/// Describes an operand in the kernel of a pipelined loop. Characteristics of
/// the operand are discovered, such as how many in-loop PHIs it has to jump
/// through and defaults for these phis.
class KernelOperandInfo {
MachineBasicBlock *BB;
MachineRegisterInfo &MRI;
SmallVector<Register, 4> PhiDefaults;
MachineOperand *Source;
MachineOperand *Target;
public:
KernelOperandInfo(MachineOperand *MO, MachineRegisterInfo &MRI,
const SmallPtrSetImpl<MachineInstr *> &IllegalPhis)
: MRI(MRI) {
Source = MO;
BB = MO->getParent()->getParent();
while (isRegInLoop(MO)) {
MachineInstr *MI = MRI.getVRegDef(MO->getReg());
if (MI->isFullCopy()) {
MO = &MI->getOperand(1);
continue;
}
if (!MI->isPHI())
break;
// If this is an illegal phi, don't count it in distance.
if (IllegalPhis.count(MI)) {
MO = &MI->getOperand(3);
continue;
}
Register Default = getInitPhiReg(*MI, BB);
MO = MI->getOperand(2).getMBB() == BB ? &MI->getOperand(1)
: &MI->getOperand(3);
PhiDefaults.push_back(Default);
}
Target = MO;
}
bool operator==(const KernelOperandInfo &Other) const {
return PhiDefaults.size() == Other.PhiDefaults.size();
}
void print(raw_ostream &OS) const {
OS << "use of " << *Source << ": distance(" << PhiDefaults.size() << ") in "
<< *Source->getParent();
}
private:
bool isRegInLoop(MachineOperand *MO) {
return MO->isReg() && MO->getReg().isVirtual() &&
MRI.getVRegDef(MO->getReg())->getParent() == BB;
}
};
} // namespace
MachineBasicBlock *
PeelingModuloScheduleExpander::peelKernel(LoopPeelDirection LPD) {
MachineBasicBlock *NewBB = PeelSingleBlockLoop(LPD, BB, MRI, TII);
if (LPD == LPD_Front)
PeeledFront.push_back(NewBB);
else
PeeledBack.push_front(NewBB);
for (auto I = BB->begin(), NI = NewBB->begin(); !I->isTerminator();
++I, ++NI) {
CanonicalMIs[&*I] = &*I;
CanonicalMIs[&*NI] = &*I;
BlockMIs[{NewBB, &*I}] = &*NI;
BlockMIs[{BB, &*I}] = &*I;
}
return NewBB;
}
void PeelingModuloScheduleExpander::filterInstructions(MachineBasicBlock *MB,
int MinStage) {
for (auto I = MB->getFirstInstrTerminator()->getReverseIterator();
I != std::next(MB->getFirstNonPHI()->getReverseIterator());) {
MachineInstr *MI = &*I++;
int Stage = getStage(MI);
if (Stage == -1 || Stage >= MinStage)
continue;
for (MachineOperand &DefMO : MI->defs()) {
SmallVector<std::pair<MachineInstr *, Register>, 4> Subs;
for (MachineInstr &UseMI : MRI.use_instructions(DefMO.getReg())) {
// Only PHIs can use values from this block by construction.
// Match with the equivalent PHI in B.
assert(UseMI.isPHI());
Register Reg = getEquivalentRegisterIn(UseMI.getOperand(0).getReg(),
MI->getParent());
Subs.emplace_back(&UseMI, Reg);
}
for (auto &Sub : Subs)
Sub.first->substituteRegister(DefMO.getReg(), Sub.second, /*SubIdx=*/0,
*MRI.getTargetRegisterInfo());
}
if (LIS)
LIS->RemoveMachineInstrFromMaps(*MI);
MI->eraseFromParent();
}
}
void PeelingModuloScheduleExpander::moveStageBetweenBlocks(
MachineBasicBlock *DestBB, MachineBasicBlock *SourceBB, unsigned Stage) {
auto InsertPt = DestBB->getFirstNonPHI();
DenseMap<Register, Register> Remaps;
for (MachineInstr &MI : llvm::make_early_inc_range(
llvm::make_range(SourceBB->getFirstNonPHI(), SourceBB->end()))) {
if (MI.isPHI()) {
// This is an illegal PHI. If we move any instructions using an illegal
// PHI, we need to create a legal Phi.
if (getStage(&MI) != Stage) {
// The legal Phi is not necessary if the illegal phi's stage
// is being moved.
Register PhiR = MI.getOperand(0).getReg();
auto RC = MRI.getRegClass(PhiR);
Register NR = MRI.createVirtualRegister(RC);
MachineInstr *NI = BuildMI(*DestBB, DestBB->getFirstNonPHI(),
DebugLoc(), TII->get(TargetOpcode::PHI), NR)
.addReg(PhiR)
.addMBB(SourceBB);
BlockMIs[{DestBB, CanonicalMIs[&MI]}] = NI;
CanonicalMIs[NI] = CanonicalMIs[&MI];
Remaps[PhiR] = NR;
}
}
if (getStage(&MI) != Stage)
continue;
MI.removeFromParent();
DestBB->insert(InsertPt, &MI);
auto *KernelMI = CanonicalMIs[&MI];
BlockMIs[{DestBB, KernelMI}] = &MI;
BlockMIs.erase({SourceBB, KernelMI});
}
SmallVector<MachineInstr *, 4> PhiToDelete;
for (MachineInstr &MI : DestBB->phis()) {
assert(MI.getNumOperands() == 3);
MachineInstr *Def = MRI.getVRegDef(MI.getOperand(1).getReg());
// If the instruction referenced by the phi is moved inside the block
// we don't need the phi anymore.
if (getStage(Def) == Stage) {
Register PhiReg = MI.getOperand(0).getReg();
assert(Def->findRegisterDefOperandIdx(MI.getOperand(1).getReg()) != -1);
MRI.replaceRegWith(MI.getOperand(0).getReg(), MI.getOperand(1).getReg());
MI.getOperand(0).setReg(PhiReg);
PhiToDelete.push_back(&MI);
}
}
for (auto *P : PhiToDelete)
P->eraseFromParent();
InsertPt = DestBB->getFirstNonPHI();
// Helper to clone Phi instructions into the destination block. We clone Phi
// greedily to avoid combinatorial explosion of Phi instructions.
auto clonePhi = [&](MachineInstr *Phi) {
MachineInstr *NewMI = MF.CloneMachineInstr(Phi);
DestBB->insert(InsertPt, NewMI);
Register OrigR = Phi->getOperand(0).getReg();
Register R = MRI.createVirtualRegister(MRI.getRegClass(OrigR));
NewMI->getOperand(0).setReg(R);
NewMI->getOperand(1).setReg(OrigR);
NewMI->getOperand(2).setMBB(*DestBB->pred_begin());
Remaps[OrigR] = R;
CanonicalMIs[NewMI] = CanonicalMIs[Phi];
BlockMIs[{DestBB, CanonicalMIs[Phi]}] = NewMI;
PhiNodeLoopIteration[NewMI] = PhiNodeLoopIteration[Phi];
return R;
};
for (auto I = DestBB->getFirstNonPHI(); I != DestBB->end(); ++I) {
for (MachineOperand &MO : I->uses()) {
if (!MO.isReg())
continue;
if (Remaps.count(MO.getReg()))
MO.setReg(Remaps[MO.getReg()]);
else {
// If we are using a phi from the source block we need to add a new phi
// pointing to the old one.
MachineInstr *Use = MRI.getUniqueVRegDef(MO.getReg());
if (Use && Use->isPHI() && Use->getParent() == SourceBB) {
Register R = clonePhi(Use);
MO.setReg(R);
}
}
}
}
}
Register
PeelingModuloScheduleExpander::getPhiCanonicalReg(MachineInstr *CanonicalPhi,
MachineInstr *Phi) {
unsigned distance = PhiNodeLoopIteration[Phi];
MachineInstr *CanonicalUse = CanonicalPhi;
Register CanonicalUseReg = CanonicalUse->getOperand(0).getReg();
for (unsigned I = 0; I < distance; ++I) {
assert(CanonicalUse->isPHI());
assert(CanonicalUse->getNumOperands() == 5);
unsigned LoopRegIdx = 3, InitRegIdx = 1;
if (CanonicalUse->getOperand(2).getMBB() == CanonicalUse->getParent())
std::swap(LoopRegIdx, InitRegIdx);
CanonicalUseReg = CanonicalUse->getOperand(LoopRegIdx).getReg();
CanonicalUse = MRI.getVRegDef(CanonicalUseReg);
}
return CanonicalUseReg;
}
void PeelingModuloScheduleExpander::peelPrologAndEpilogs() {
BitVector LS(Schedule.getNumStages(), true);
BitVector AS(Schedule.getNumStages(), true);
LiveStages[BB] = LS;
AvailableStages[BB] = AS;
// Peel out the prologs.
LS.reset();
for (int I = 0; I < Schedule.getNumStages() - 1; ++I) {
LS[I] = true;
Prologs.push_back(peelKernel(LPD_Front));
LiveStages[Prologs.back()] = LS;
AvailableStages[Prologs.back()] = LS;
}
// Create a block that will end up as the new loop exiting block (dominated by
// all prologs and epilogs). It will only contain PHIs, in the same order as
// BB's PHIs. This gives us a poor-man's LCSSA with the inductive property
// that the exiting block is a (sub) clone of BB. This in turn gives us the
// property that any value deffed in BB but used outside of BB is used by a
// PHI in the exiting block.
MachineBasicBlock *ExitingBB = CreateLCSSAExitingBlock();
EliminateDeadPhis(ExitingBB, MRI, LIS, /*KeepSingleSrcPhi=*/true);
// Push out the epilogs, again in reverse order.
// We can't assume anything about the minumum loop trip count at this point,
// so emit a fairly complex epilog.
// We first peel number of stages minus one epilogue. Then we remove dead
// stages and reorder instructions based on their stage. If we have 3 stages
// we generate first:
// E0[3, 2, 1]
// E1[3', 2']
// E2[3'']
// And then we move instructions based on their stages to have:
// E0[3]
// E1[2, 3']
// E2[1, 2', 3'']
// The transformation is legal because we only move instructions past
// instructions of a previous loop iteration.
for (int I = 1; I <= Schedule.getNumStages() - 1; ++I) {
Epilogs.push_back(peelKernel(LPD_Back));
MachineBasicBlock *B = Epilogs.back();
filterInstructions(B, Schedule.getNumStages() - I);
// Keep track at which iteration each phi belongs to. We need it to know
// what version of the variable to use during prologue/epilogue stitching.
EliminateDeadPhis(B, MRI, LIS, /*KeepSingleSrcPhi=*/true);
for (MachineInstr &Phi : B->phis())
PhiNodeLoopIteration[&Phi] = Schedule.getNumStages() - I;
}
for (size_t I = 0; I < Epilogs.size(); I++) {
LS.reset();
for (size_t J = I; J < Epilogs.size(); J++) {
int Iteration = J;
unsigned Stage = Schedule.getNumStages() - 1 + I - J;
// Move stage one block at a time so that Phi nodes are updated correctly.
for (size_t K = Iteration; K > I; K--)
moveStageBetweenBlocks(Epilogs[K - 1], Epilogs[K], Stage);
LS[Stage] = true;
}
LiveStages[Epilogs[I]] = LS;
AvailableStages[Epilogs[I]] = AS;
}
// Now we've defined all the prolog and epilog blocks as a fallthrough
// sequence, add the edges that will be followed if the loop trip count is
// lower than the number of stages (connecting prologs directly with epilogs).
auto PI = Prologs.begin();
auto EI = Epilogs.begin();
assert(Prologs.size() == Epilogs.size());
for (; PI != Prologs.end(); ++PI, ++EI) {
MachineBasicBlock *Pred = *(*EI)->pred_begin();
(*PI)->addSuccessor(*EI);
for (MachineInstr &MI : (*EI)->phis()) {
Register Reg = MI.getOperand(1).getReg();
MachineInstr *Use = MRI.getUniqueVRegDef(Reg);
if (Use && Use->getParent() == Pred) {
MachineInstr *CanonicalUse = CanonicalMIs[Use];
if (CanonicalUse->isPHI()) {
// If the use comes from a phi we need to skip as many phi as the
// distance between the epilogue and the kernel. Trace through the phi
// chain to find the right value.
Reg = getPhiCanonicalReg(CanonicalUse, Use);
}
Reg = getEquivalentRegisterIn(Reg, *PI);
}
MI.addOperand(MachineOperand::CreateReg(Reg, /*isDef=*/false));
MI.addOperand(MachineOperand::CreateMBB(*PI));
}
}
// Create a list of all blocks in order.
SmallVector<MachineBasicBlock *, 8> Blocks;
llvm::copy(PeeledFront, std::back_inserter(Blocks));
Blocks.push_back(BB);
llvm::copy(PeeledBack, std::back_inserter(Blocks));
// Iterate in reverse order over all instructions, remapping as we go.
for (MachineBasicBlock *B : reverse(Blocks)) {
for (auto I = B->getFirstInstrTerminator()->getReverseIterator();
I != std::next(B->getFirstNonPHI()->getReverseIterator());) {
MachineInstr *MI = &*I++;
rewriteUsesOf(MI);
}
}
for (auto *MI : IllegalPhisToDelete) {
if (LIS)
LIS->RemoveMachineInstrFromMaps(*MI);
MI->eraseFromParent();
}
IllegalPhisToDelete.clear();
// Now all remapping has been done, we're free to optimize the generated code.
for (MachineBasicBlock *B : reverse(Blocks))
EliminateDeadPhis(B, MRI, LIS);
EliminateDeadPhis(ExitingBB, MRI, LIS);
}
MachineBasicBlock *PeelingModuloScheduleExpander::CreateLCSSAExitingBlock() {
MachineFunction &MF = *BB->getParent();
MachineBasicBlock *Exit = *BB->succ_begin();
if (Exit == BB)
Exit = *std::next(BB->succ_begin());
MachineBasicBlock *NewBB = MF.CreateMachineBasicBlock(BB->getBasicBlock());
MF.insert(std::next(BB->getIterator()), NewBB);
// Clone all phis in BB into NewBB and rewrite.
for (MachineInstr &MI : BB->phis()) {
auto RC = MRI.getRegClass(MI.getOperand(0).getReg());
Register OldR = MI.getOperand(3).getReg();
Register R = MRI.createVirtualRegister(RC);
SmallVector<MachineInstr *, 4> Uses;
for (MachineInstr &Use : MRI.use_instructions(OldR))
if (Use.getParent() != BB)
Uses.push_back(&Use);
for (MachineInstr *Use : Uses)
Use->substituteRegister(OldR, R, /*SubIdx=*/0,
*MRI.getTargetRegisterInfo());
MachineInstr *NI = BuildMI(NewBB, DebugLoc(), TII->get(TargetOpcode::PHI), R)
.addReg(OldR)
.addMBB(BB);
BlockMIs[{NewBB, &MI}] = NI;
CanonicalMIs[NI] = &MI;
}
BB->replaceSuccessor(Exit, NewBB);
Exit->replacePhiUsesWith(BB, NewBB);
NewBB->addSuccessor(Exit);
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
bool CanAnalyzeBr = !TII->analyzeBranch(*BB, TBB, FBB, Cond);
(void)CanAnalyzeBr;
assert(CanAnalyzeBr && "Must be able to analyze the loop branch!");
TII->removeBranch(*BB);
TII->insertBranch(*BB, TBB == Exit ? NewBB : TBB, FBB == Exit ? NewBB : FBB,
Cond, DebugLoc());
TII->insertUnconditionalBranch(*NewBB, Exit, DebugLoc());
return NewBB;
}
Register
PeelingModuloScheduleExpander::getEquivalentRegisterIn(Register Reg,
MachineBasicBlock *BB) {
MachineInstr *MI = MRI.getUniqueVRegDef(Reg);
unsigned OpIdx = MI->findRegisterDefOperandIdx(Reg);
return BlockMIs[{BB, CanonicalMIs[MI]}]->getOperand(OpIdx).getReg();
}
void PeelingModuloScheduleExpander::rewriteUsesOf(MachineInstr *MI) {
if (MI->isPHI()) {
// This is an illegal PHI. The loop-carried (desired) value is operand 3,
// and it is produced by this block.
Register PhiR = MI->getOperand(0).getReg();
Register R = MI->getOperand(3).getReg();
int RMIStage = getStage(MRI.getUniqueVRegDef(R));
if (RMIStage != -1 && !AvailableStages[MI->getParent()].test(RMIStage))
R = MI->getOperand(1).getReg();
MRI.setRegClass(R, MRI.getRegClass(PhiR));
MRI.replaceRegWith(PhiR, R);
// Postpone deleting the Phi as it may be referenced by BlockMIs and used
// later to figure out how to remap registers.
MI->getOperand(0).setReg(PhiR);
IllegalPhisToDelete.push_back(MI);
return;
}
int Stage = getStage(MI);
if (Stage == -1 || LiveStages.count(MI->getParent()) == 0 ||
LiveStages[MI->getParent()].test(Stage))
// Instruction is live, no rewriting to do.
return;
for (MachineOperand &DefMO : MI->defs()) {
SmallVector<std::pair<MachineInstr *, Register>, 4> Subs;
for (MachineInstr &UseMI : MRI.use_instructions(DefMO.getReg())) {
// Only PHIs can use values from this block by construction.
// Match with the equivalent PHI in B.
assert(UseMI.isPHI());
Register Reg = getEquivalentRegisterIn(UseMI.getOperand(0).getReg(),
MI->getParent());
Subs.emplace_back(&UseMI, Reg);
}
for (auto &Sub : Subs)
Sub.first->substituteRegister(DefMO.getReg(), Sub.second, /*SubIdx=*/0,
*MRI.getTargetRegisterInfo());
}
if (LIS)
LIS->RemoveMachineInstrFromMaps(*MI);
MI->eraseFromParent();
}
void PeelingModuloScheduleExpander::fixupBranches() {
// Work outwards from the kernel.
bool KernelDisposed = false;
int TC = Schedule.getNumStages() - 1;
for (auto PI = Prologs.rbegin(), EI = Epilogs.rbegin(); PI != Prologs.rend();
++PI, ++EI, --TC) {
MachineBasicBlock *Prolog = *PI;
MachineBasicBlock *Fallthrough = *Prolog->succ_begin();
MachineBasicBlock *Epilog = *EI;
SmallVector<MachineOperand, 4> Cond;
TII->removeBranch(*Prolog);
Optional<bool> StaticallyGreater =
LoopInfo->createTripCountGreaterCondition(TC, *Prolog, Cond);
if (!StaticallyGreater.hasValue()) {
LLVM_DEBUG(dbgs() << "Dynamic: TC > " << TC << "\n");
// Dynamically branch based on Cond.
TII->insertBranch(*Prolog, Epilog, Fallthrough, Cond, DebugLoc());
} else if (*StaticallyGreater == false) {
LLVM_DEBUG(dbgs() << "Static-false: TC > " << TC << "\n");
// Prolog never falls through; branch to epilog and orphan interior
// blocks. Leave it to unreachable-block-elim to clean up.
Prolog->removeSuccessor(Fallthrough);
for (MachineInstr &P : Fallthrough->phis()) {
P.removeOperand(2);
P.removeOperand(1);
}
TII->insertUnconditionalBranch(*Prolog, Epilog, DebugLoc());
KernelDisposed = true;
} else {
LLVM_DEBUG(dbgs() << "Static-true: TC > " << TC << "\n");
// Prolog always falls through; remove incoming values in epilog.
Prolog->removeSuccessor(Epilog);
for (MachineInstr &P : Epilog->phis()) {
P.removeOperand(4);
P.removeOperand(3);
}
}
}
if (!KernelDisposed) {
LoopInfo->adjustTripCount(-(Schedule.getNumStages() - 1));
LoopInfo->setPreheader(Prologs.back());
} else {
LoopInfo->disposed();
}
}
void PeelingModuloScheduleExpander::rewriteKernel() {
KernelRewriter KR(*Schedule.getLoop(), Schedule, BB);
KR.rewrite();
}
void PeelingModuloScheduleExpander::expand() {
BB = Schedule.getLoop()->getTopBlock();
Preheader = Schedule.getLoop()->getLoopPreheader();
LLVM_DEBUG(Schedule.dump());
LoopInfo = TII->analyzeLoopForPipelining(BB);
assert(LoopInfo);
rewriteKernel();
peelPrologAndEpilogs();
fixupBranches();
}
void PeelingModuloScheduleExpander::validateAgainstModuloScheduleExpander() {
BB = Schedule.getLoop()->getTopBlock();
Preheader = Schedule.getLoop()->getLoopPreheader();
// Dump the schedule before we invalidate and remap all its instructions.
// Stash it in a string so we can print it if we found an error.
std::string ScheduleDump;
raw_string_ostream OS(ScheduleDump);
Schedule.print(OS);
OS.flush();
// First, run the normal ModuleScheduleExpander. We don't support any
// InstrChanges.
assert(LIS && "Requires LiveIntervals!");
ModuloScheduleExpander MSE(MF, Schedule, *LIS,
ModuloScheduleExpander::InstrChangesTy());
MSE.expand();
MachineBasicBlock *ExpandedKernel = MSE.getRewrittenKernel();
if (!ExpandedKernel) {
// The expander optimized away the kernel. We can't do any useful checking.
MSE.cleanup();
return;
}
// Before running the KernelRewriter, re-add BB into the CFG.
Preheader->addSuccessor(BB);
// Now run the new expansion algorithm.
KernelRewriter KR(*Schedule.getLoop(), Schedule, BB);
KR.rewrite();
peelPrologAndEpilogs();
// Collect all illegal phis that the new algorithm created. We'll give these
// to KernelOperandInfo.
SmallPtrSet<MachineInstr *, 4> IllegalPhis;
for (auto NI = BB->getFirstNonPHI(); NI != BB->end(); ++NI) {
if (NI->isPHI())
IllegalPhis.insert(&*NI);
}
// Co-iterate across both kernels. We expect them to be identical apart from
// phis and full COPYs (we look through both).
SmallVector<std::pair<KernelOperandInfo, KernelOperandInfo>, 8> KOIs;
auto OI = ExpandedKernel->begin();
auto NI = BB->begin();
for (; !OI->isTerminator() && !NI->isTerminator(); ++OI, ++NI) {
while (OI->isPHI() || OI->isFullCopy())
++OI;
while (NI->isPHI() || NI->isFullCopy())
++NI;
assert(OI->getOpcode() == NI->getOpcode() && "Opcodes don't match?!");
// Analyze every operand separately.
for (auto OOpI = OI->operands_begin(), NOpI = NI->operands_begin();
OOpI != OI->operands_end(); ++OOpI, ++NOpI)
KOIs.emplace_back(KernelOperandInfo(&*OOpI, MRI, IllegalPhis),
KernelOperandInfo(&*NOpI, MRI, IllegalPhis));
}
bool Failed = false;
for (auto &OldAndNew : KOIs) {
if (OldAndNew.first == OldAndNew.second)
continue;
Failed = true;
errs() << "Modulo kernel validation error: [\n";
errs() << " [golden] ";
OldAndNew.first.print(errs());
errs() << " ";
OldAndNew.second.print(errs());
errs() << "]\n";
}
if (Failed) {
errs() << "Golden reference kernel:\n";
ExpandedKernel->print(errs());
errs() << "New kernel:\n";
BB->print(errs());
errs() << ScheduleDump;
report_fatal_error(
"Modulo kernel validation (-pipeliner-experimental-cg) failed");
}
// Cleanup by removing BB from the CFG again as the original
// ModuloScheduleExpander intended.
Preheader->removeSuccessor(BB);
MSE.cleanup();
}
//===----------------------------------------------------------------------===//
// ModuloScheduleTestPass implementation
//===----------------------------------------------------------------------===//
// This pass constructs a ModuloSchedule from its module and runs
// ModuloScheduleExpander.
//
// The module is expected to contain a single-block analyzable loop.
// The total order of instructions is taken from the loop as-is.
// Instructions are expected to be annotated with a PostInstrSymbol.
// This PostInstrSymbol must have the following format:
// "Stage=%d Cycle=%d".
//===----------------------------------------------------------------------===//
namespace {
class ModuloScheduleTest : public MachineFunctionPass {
public:
static char ID;
ModuloScheduleTest() : MachineFunctionPass(ID) {
initializeModuloScheduleTestPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
void runOnLoop(MachineFunction &MF, MachineLoop &L);
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineLoopInfo>();
AU.addRequired<LiveIntervals>();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // namespace
char ModuloScheduleTest::ID = 0;
INITIALIZE_PASS_BEGIN(ModuloScheduleTest, "modulo-schedule-test",
"Modulo Schedule test pass", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(ModuloScheduleTest, "modulo-schedule-test",
"Modulo Schedule test pass", false, false)
bool ModuloScheduleTest::runOnMachineFunction(MachineFunction &MF) {
MachineLoopInfo &MLI = getAnalysis<MachineLoopInfo>();
for (auto *L : MLI) {
if (L->getTopBlock() != L->getBottomBlock())
continue;
runOnLoop(MF, *L);
return false;
}
return false;
}
static void parseSymbolString(StringRef S, int &Cycle, int &Stage) {
std::pair<StringRef, StringRef> StageAndCycle = getToken(S, "_");
std::pair<StringRef, StringRef> StageTokenAndValue =
getToken(StageAndCycle.first, "-");
std::pair<StringRef, StringRef> CycleTokenAndValue =
getToken(StageAndCycle.second, "-");
if (StageTokenAndValue.first != "Stage" ||
CycleTokenAndValue.first != "_Cycle") {
llvm_unreachable(
"Bad post-instr symbol syntax: see comment in ModuloScheduleTest");
return;
}
StageTokenAndValue.second.drop_front().getAsInteger(10, Stage);
CycleTokenAndValue.second.drop_front().getAsInteger(10, Cycle);
dbgs() << " Stage=" << Stage << ", Cycle=" << Cycle << "\n";
}
void ModuloScheduleTest::runOnLoop(MachineFunction &MF, MachineLoop &L) {
LiveIntervals &LIS = getAnalysis<LiveIntervals>();
MachineBasicBlock *BB = L.getTopBlock();
dbgs() << "--- ModuloScheduleTest running on BB#" << BB->getNumber() << "\n";
DenseMap<MachineInstr *, int> Cycle, Stage;
std::vector<MachineInstr *> Instrs;
for (MachineInstr &MI : *BB) {
if (MI.isTerminator())
continue;
Instrs.push_back(&MI);
if (MCSymbol *Sym = MI.getPostInstrSymbol()) {
dbgs() << "Parsing post-instr symbol for " << MI;
parseSymbolString(Sym->getName(), Cycle[&MI], Stage[&MI]);
}
}
ModuloSchedule MS(MF, &L, std::move(Instrs), std::move(Cycle),
std::move(Stage));
ModuloScheduleExpander MSE(
MF, MS, LIS, /*InstrChanges=*/ModuloScheduleExpander::InstrChangesTy());
MSE.expand();
MSE.cleanup();
}
//===----------------------------------------------------------------------===//
// ModuloScheduleTestAnnotater implementation
//===----------------------------------------------------------------------===//
void ModuloScheduleTestAnnotater::annotate() {
for (MachineInstr *MI : S.getInstructions()) {
SmallVector<char, 16> SV;
raw_svector_ostream OS(SV);
OS << "Stage-" << S.getStage(MI) << "_Cycle-" << S.getCycle(MI);
MCSymbol *Sym = MF.getContext().getOrCreateSymbol(OS.str());
MI->setPostInstrSymbol(MF, Sym);
}
}
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