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llvm-mirror/lib/CodeGen/ModuloSchedule.cpp
Hendrik Greving 36b5d3f1af [ModuloSchedule] Pass loop block explicitly to kernel rewriter. 
This change is NFC upstream. We pass in the loop's block to the kernel
rewriter explicitly, instead of assuming it's the loop's top block. This
change is made for downstream targets where this assumption doesn't hold.

Differential Revision: https://reviews.llvm.org/D104811
2021-06-25 09:51:22 -07:00

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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/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 (unsigned i = 0, e = MI->getNumOperands(); i < e; ++i) {
MachineOperand &Op = MI->getOperand(i);
if (!Op.isReg() || !Op.isDef())
continue;
Register Reg = Op.getReg();
unsigned MaxDiff = 0;
bool PhiIsSwapped = false;
for (MachineRegisterInfo::use_iterator UI = MRI.use_begin(Reg),
EI = MRI.use_end();
UI != EI; ++UI) {
MachineOperand &UseOp = *UI;
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 (MachineBasicBlock::iterator I = BB->getFirstTerminator(),
E = BB->instr_end();
I != E; ++I) {
MachineInstr *NewMI = MF.CloneMachineInstr(&*I);
updateInstruction(NewMI, false, MaxStageCount, 0, VRMap);
KernelBB->push_back(NewMI);
InstrMap[NewMI] = &*I;
}
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 (MachineRegisterInfo::use_iterator I = MRI.use_begin(FromReg),
E = MRI.use_end();
I != E;) {
MachineOperand &O = *I;
++I;
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 (MachineRegisterInfo::use_iterator I = MRI.use_begin(Reg),
E = MRI.use_end();
I != E; ++I)
if (I->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 (MBBVectorTy::reverse_iterator MBB = EpilogBBs.rbegin(),
MBE = EpilogBBs.rend();
MBB != MBE; ++MBB)
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 (MachineInstr::mop_iterator MOI = MI->operands_begin(),
MOE = MI->operands_end();
MOI != MOE; ++MOI) {
if (!MOI->isReg() || !MOI->isDef())
continue;
Register reg = MOI->getReg();
// Assume physical registers are used, unless they are marked dead.
if (Register::isPhysicalRegister(reg)) {
used = !MOI->isDead();
if (used)
break;
continue;
}
unsigned realUses = 0;
for (MachineRegisterInfo::use_iterator UI = MRI.use_begin(reg),
EI = MRI.use_end();
UI != EI; ++UI) {
// Check if there are any uses that occur only in the original
// loop. If so, that's not a real use.
if (UI->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 (MachineBasicBlock::iterator BBI = KernelBB->instr_begin(),
BBE = KernelBB->getFirstNonPHI();
BBI != BBE;) {
MachineInstr *MI = &*BBI;
++BBI;
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 (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = NewMI->getOperand(i);
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 (MachineRegisterInfo::use_iterator UI = MRI.use_begin(OldReg),
EI = MRI.use_end();
UI != EI;) {
MachineOperand &UseOp = *UI;
MachineInstr *UseMI = UseOp.getParent();
++UI;
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 (auto I = MBB->begin(); I != MBB->getFirstNonPHI();) {
MachineInstr &MI = *I++;
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 (auto I = SourceBB->getFirstNonPHI(); I != SourceBB->end();) {
MachineInstr *MI = &*I++;
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] = 1;
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 (auto Phi = B->begin(), IE = B->getFirstNonPHI(); Phi != IE; ++Phi)
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] = 1;
}
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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