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llvm/lib/CodeGen/MachineBasicBlock.cpp
Quentin Colombet 1b369e43d3 [MachineBasicBlock] Take advantage of the partially dead information. 
Thanks to that information we wouldn't lie on a register being live whereas it
is not.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267622 91177308-0d34-0410-b5e6-96231b3b80d8
2016-04-26 23:14:29 +00:00

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//===-- llvm/CodeGen/MachineBasicBlock.cpp ----------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Collect the sequence of machine instructions for a basic block.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/ModuleSlotTracker.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <algorithm>
using namespace llvm;
#define DEBUG_TYPE "codegen"
MachineBasicBlock::MachineBasicBlock(MachineFunction &MF, const BasicBlock *B)
: BB(B), Number(-1), xParent(&MF) {
Insts.Parent = this;
}
MachineBasicBlock::~MachineBasicBlock() {
}
/// Return the MCSymbol for this basic block.
MCSymbol *MachineBasicBlock::getSymbol() const {
if (!CachedMCSymbol) {
const MachineFunction *MF = getParent();
MCContext &Ctx = MF->getContext();
const char *Prefix = Ctx.getAsmInfo()->getPrivateLabelPrefix();
assert(getNumber() >= 0 && "cannot get label for unreachable MBB");
CachedMCSymbol = Ctx.getOrCreateSymbol(Twine(Prefix) + "BB" +
Twine(MF->getFunctionNumber()) +
"_" + Twine(getNumber()));
}
return CachedMCSymbol;
}
raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
MBB.print(OS);
return OS;
}
/// When an MBB is added to an MF, we need to update the parent pointer of the
/// MBB, the MBB numbering, and any instructions in the MBB to be on the right
/// operand list for registers.
///
/// MBBs start out as #-1. When a MBB is added to a MachineFunction, it
/// gets the next available unique MBB number. If it is removed from a
/// MachineFunction, it goes back to being #-1.
void ilist_traits<MachineBasicBlock>::addNodeToList(MachineBasicBlock *N) {
MachineFunction &MF = *N->getParent();
N->Number = MF.addToMBBNumbering(N);
// Make sure the instructions have their operands in the reginfo lists.
MachineRegisterInfo &RegInfo = MF.getRegInfo();
for (MachineBasicBlock::instr_iterator
I = N->instr_begin(), E = N->instr_end(); I != E; ++I)
I->AddRegOperandsToUseLists(RegInfo);
}
void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
N->getParent()->removeFromMBBNumbering(N->Number);
N->Number = -1;
}
/// When we add an instruction to a basic block list, we update its parent
/// pointer and add its operands from reg use/def lists if appropriate.
void ilist_traits<MachineInstr>::addNodeToList(MachineInstr *N) {
assert(!N->getParent() && "machine instruction already in a basic block");
N->setParent(Parent);
// Add the instruction's register operands to their corresponding
// use/def lists.
MachineFunction *MF = Parent->getParent();
N->AddRegOperandsToUseLists(MF->getRegInfo());
}
/// When we remove an instruction from a basic block list, we update its parent
/// pointer and remove its operands from reg use/def lists if appropriate.
void ilist_traits<MachineInstr>::removeNodeFromList(MachineInstr *N) {
assert(N->getParent() && "machine instruction not in a basic block");
// Remove from the use/def lists.
if (MachineFunction *MF = N->getParent()->getParent())
N->RemoveRegOperandsFromUseLists(MF->getRegInfo());
N->setParent(nullptr);
}
/// When moving a range of instructions from one MBB list to another, we need to
/// update the parent pointers and the use/def lists.
void ilist_traits<MachineInstr>::
transferNodesFromList(ilist_traits<MachineInstr> &FromList,
ilist_iterator<MachineInstr> First,
ilist_iterator<MachineInstr> Last) {
assert(Parent->getParent() == FromList.Parent->getParent() &&
"MachineInstr parent mismatch!");
// Splice within the same MBB -> no change.
if (Parent == FromList.Parent) return;
// If splicing between two blocks within the same function, just update the
// parent pointers.
for (; First != Last; ++First)
First->setParent(Parent);
}
void ilist_traits<MachineInstr>::deleteNode(MachineInstr* MI) {
assert(!MI->getParent() && "MI is still in a block!");
Parent->getParent()->DeleteMachineInstr(MI);
}
MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
instr_iterator I = instr_begin(), E = instr_end();
while (I != E && I->isPHI())
++I;
assert((I == E || !I->isInsideBundle()) &&
"First non-phi MI cannot be inside a bundle!");
return I;
}
MachineBasicBlock::iterator
MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
iterator E = end();
while (I != E && (I->isPHI() || I->isPosition() || I->isDebugValue()))
++I;
// FIXME: This needs to change if we wish to bundle labels / dbg_values
// inside the bundle.
assert((I == E || !I->isInsideBundle()) &&
"First non-phi / non-label instruction is inside a bundle!");
return I;
}
MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
iterator B = begin(), E = end(), I = E;
while (I != B && ((--I)->isTerminator() || I->isDebugValue()))
; /*noop */
while (I != E && !I->isTerminator())
++I;
return I;
}
MachineBasicBlock::instr_iterator MachineBasicBlock::getFirstInstrTerminator() {
instr_iterator B = instr_begin(), E = instr_end(), I = E;
while (I != B && ((--I)->isTerminator() || I->isDebugValue()))
; /*noop */
while (I != E && !I->isTerminator())
++I;
return I;
}
MachineBasicBlock::iterator MachineBasicBlock::getFirstNonDebugInstr() {
// Skip over begin-of-block dbg_value instructions.
iterator I = begin(), E = end();
while (I != E && I->isDebugValue())
++I;
return I;
}
MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {
// Skip over end-of-block dbg_value instructions.
instr_iterator B = instr_begin(), I = instr_end();
while (I != B) {
--I;
// Return instruction that starts a bundle.
if (I->isDebugValue() || I->isInsideBundle())
continue;
return I;
}
// The block is all debug values.
return end();
}
bool MachineBasicBlock::hasEHPadSuccessor() const {
for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I)
if ((*I)->isEHPad())
return true;
return false;
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void MachineBasicBlock::dump() const {
print(dbgs());
}
#endif
StringRef MachineBasicBlock::getName() const {
if (const BasicBlock *LBB = getBasicBlock())
return LBB->getName();
else
return "(null)";
}
/// Return a hopefully unique identifier for this block.
std::string MachineBasicBlock::getFullName() const {
std::string Name;
if (getParent())
Name = (getParent()->getName() + ":").str();
if (getBasicBlock())
Name += getBasicBlock()->getName();
else
Name += ("BB" + Twine(getNumber())).str();
return Name;
}
void MachineBasicBlock::print(raw_ostream &OS, SlotIndexes *Indexes) const {
const MachineFunction *MF = getParent();
if (!MF) {
OS << "Can't print out MachineBasicBlock because parent MachineFunction"
<< " is null\n";
return;
}
const Function *F = MF->getFunction();
const Module *M = F ? F->getParent() : nullptr;
ModuleSlotTracker MST(M);
print(OS, MST, Indexes);
}
void MachineBasicBlock::print(raw_ostream &OS, ModuleSlotTracker &MST,
SlotIndexes *Indexes) const {
const MachineFunction *MF = getParent();
if (!MF) {
OS << "Can't print out MachineBasicBlock because parent MachineFunction"
<< " is null\n";
return;
}
if (Indexes)
OS << Indexes->getMBBStartIdx(this) << '\t';
OS << "BB#" << getNumber() << ": ";
const char *Comma = "";
if (const BasicBlock *LBB = getBasicBlock()) {
OS << Comma << "derived from LLVM BB ";
LBB->printAsOperand(OS, /*PrintType=*/false, MST);
Comma = ", ";
}
if (isEHPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
if (Alignment)
OS << Comma << "Align " << Alignment << " (" << (1u << Alignment)
<< " bytes)";
OS << '\n';
const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
if (!livein_empty()) {
if (Indexes) OS << '\t';
OS << " Live Ins:";
for (const auto &LI : make_range(livein_begin(), livein_end())) {
OS << ' ' << PrintReg(LI.PhysReg, TRI);
if (LI.LaneMask != ~0u)
OS << ':' << PrintLaneMask(LI.LaneMask);
}
OS << '\n';
}
// Print the preds of this block according to the CFG.
if (!pred_empty()) {
if (Indexes) OS << '\t';
OS << " Predecessors according to CFG:";
for (const_pred_iterator PI = pred_begin(), E = pred_end(); PI != E; ++PI)
OS << " BB#" << (*PI)->getNumber();
OS << '\n';
}
for (auto &I : instrs()) {
if (Indexes) {
if (Indexes->hasIndex(I))
OS << Indexes->getInstructionIndex(I);
OS << '\t';
}
OS << '\t';
if (I.isInsideBundle())
OS << " * ";
I.print(OS, MST);
}
// Print the successors of this block according to the CFG.
if (!succ_empty()) {
if (Indexes) OS << '\t';
OS << " Successors according to CFG:";
for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI) {
OS << " BB#" << (*SI)->getNumber();
if (!Probs.empty())
OS << '(' << *getProbabilityIterator(SI) << ')';
}
OS << '\n';
}
}
void MachineBasicBlock::printAsOperand(raw_ostream &OS,
bool /*PrintType*/) const {
OS << "BB#" << getNumber();
}
void MachineBasicBlock::removeLiveIn(MCPhysReg Reg, LaneBitmask LaneMask) {
LiveInVector::iterator I = std::find_if(
LiveIns.begin(), LiveIns.end(),
[Reg] (const RegisterMaskPair &LI) { return LI.PhysReg == Reg; });
if (I == LiveIns.end())
return;
I->LaneMask &= ~LaneMask;
if (I->LaneMask == 0)
LiveIns.erase(I);
}
bool MachineBasicBlock::isLiveIn(MCPhysReg Reg, LaneBitmask LaneMask) const {
livein_iterator I = std::find_if(
LiveIns.begin(), LiveIns.end(),
[Reg] (const RegisterMaskPair &LI) { return LI.PhysReg == Reg; });
return I != livein_end() && (I->LaneMask & LaneMask) != 0;
}
void MachineBasicBlock::sortUniqueLiveIns() {
std::sort(LiveIns.begin(), LiveIns.end(),
[](const RegisterMaskPair &LI0, const RegisterMaskPair &LI1) {
return LI0.PhysReg < LI1.PhysReg;
});
// Liveins are sorted by physreg now we can merge their lanemasks.
LiveInVector::const_iterator I = LiveIns.begin();
LiveInVector::const_iterator J;
LiveInVector::iterator Out = LiveIns.begin();
for (; I != LiveIns.end(); ++Out, I = J) {
unsigned PhysReg = I->PhysReg;
LaneBitmask LaneMask = I->LaneMask;
for (J = std::next(I); J != LiveIns.end() && J->PhysReg == PhysReg; ++J)
LaneMask |= J->LaneMask;
Out->PhysReg = PhysReg;
Out->LaneMask = LaneMask;
}
LiveIns.erase(Out, LiveIns.end());
}
unsigned
MachineBasicBlock::addLiveIn(MCPhysReg PhysReg, const TargetRegisterClass *RC) {
assert(getParent() && "MBB must be inserted in function");
assert(TargetRegisterInfo::isPhysicalRegister(PhysReg) && "Expected physreg");
assert(RC && "Register class is required");
assert((isEHPad() || this == &getParent()->front()) &&
"Only the entry block and landing pads can have physreg live ins");
bool LiveIn = isLiveIn(PhysReg);
iterator I = SkipPHIsAndLabels(begin()), E = end();
MachineRegisterInfo &MRI = getParent()->getRegInfo();
const TargetInstrInfo &TII = *getParent()->getSubtarget().getInstrInfo();
// Look for an existing copy.
if (LiveIn)
for (;I != E && I->isCopy(); ++I)
if (I->getOperand(1).getReg() == PhysReg) {
unsigned VirtReg = I->getOperand(0).getReg();
if (!MRI.constrainRegClass(VirtReg, RC))
llvm_unreachable("Incompatible live-in register class.");
return VirtReg;
}
// No luck, create a virtual register.
unsigned VirtReg = MRI.createVirtualRegister(RC);
BuildMI(*this, I, DebugLoc(), TII.get(TargetOpcode::COPY), VirtReg)
.addReg(PhysReg, RegState::Kill);
if (!LiveIn)
addLiveIn(PhysReg);
return VirtReg;
}
void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
getParent()->splice(NewAfter->getIterator(), getIterator());
}
void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
getParent()->splice(++NewBefore->getIterator(), getIterator());
}
void MachineBasicBlock::updateTerminator() {
const TargetInstrInfo *TII = getParent()->getSubtarget().getInstrInfo();
// A block with no successors has no concerns with fall-through edges.
if (this->succ_empty()) return;
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
DebugLoc DL; // FIXME: this is nowhere
bool B = TII->AnalyzeBranch(*this, TBB, FBB, Cond);
(void) B;
assert(!B && "UpdateTerminators requires analyzable predecessors!");
if (Cond.empty()) {
if (TBB) {
// The block has an unconditional branch. If its successor is now
// its layout successor, delete the branch.
if (isLayoutSuccessor(TBB))
TII->RemoveBranch(*this);
} else {
// The block has an unconditional fallthrough. If its successor is not
// its layout successor, insert a branch. First we have to locate the
// only non-landing-pad successor, as that is the fallthrough block.
for (succ_iterator SI = succ_begin(), SE = succ_end(); SI != SE; ++SI) {
if ((*SI)->isEHPad())
continue;
assert(!TBB && "Found more than one non-landing-pad successor!");
TBB = *SI;
}
// If there is no non-landing-pad successor, the block has no
// fall-through edges to be concerned with.
if (!TBB)
return;
// Finally update the unconditional successor to be reached via a branch
// if it would not be reached by fallthrough.
if (!isLayoutSuccessor(TBB))
TII->InsertBranch(*this, TBB, nullptr, Cond, DL);
}
} else {
if (FBB) {
// The block has a non-fallthrough conditional branch. If one of its
// successors is its layout successor, rewrite it to a fallthrough
// conditional branch.
if (isLayoutSuccessor(TBB)) {
if (TII->ReverseBranchCondition(Cond))
return;
TII->RemoveBranch(*this);
TII->InsertBranch(*this, FBB, nullptr, Cond, DL);
} else if (isLayoutSuccessor(FBB)) {
TII->RemoveBranch(*this);
TII->InsertBranch(*this, TBB, nullptr, Cond, DL);
}
} else {
// Walk through the successors and find the successor which is not
// a landing pad and is not the conditional branch destination (in TBB)
// as the fallthrough successor.
MachineBasicBlock *FallthroughBB = nullptr;
for (succ_iterator SI = succ_begin(), SE = succ_end(); SI != SE; ++SI) {
if ((*SI)->isEHPad() || *SI == TBB)
continue;
assert(!FallthroughBB && "Found more than one fallthrough successor.");
FallthroughBB = *SI;
}
if (!FallthroughBB && canFallThrough()) {
// We fallthrough to the same basic block as the conditional jump
// targets. Remove the conditional jump, leaving unconditional
// fallthrough.
// FIXME: This does not seem like a reasonable pattern to support, but
// it has been seen in the wild coming out of degenerate ARM test cases.
TII->RemoveBranch(*this);
// Finally update the unconditional successor to be reached via a branch
// if it would not be reached by fallthrough.
if (!isLayoutSuccessor(TBB))
TII->InsertBranch(*this, TBB, nullptr, Cond, DL);
return;
}
// The block has a fallthrough conditional branch.
if (isLayoutSuccessor(TBB)) {
if (TII->ReverseBranchCondition(Cond)) {
// We can't reverse the condition, add an unconditional branch.
Cond.clear();
TII->InsertBranch(*this, FallthroughBB, nullptr, Cond, DL);
return;
}
TII->RemoveBranch(*this);
TII->InsertBranch(*this, FallthroughBB, nullptr, Cond, DL);
} else if (!isLayoutSuccessor(FallthroughBB)) {
TII->RemoveBranch(*this);
TII->InsertBranch(*this, TBB, FallthroughBB, Cond, DL);
}
}
}
}
void MachineBasicBlock::validateSuccProbs() const {
#ifndef NDEBUG
int64_t Sum = 0;
for (auto Prob : Probs)
Sum += Prob.getNumerator();
// Due to precision issue, we assume that the sum of probabilities is one if
// the difference between the sum of their numerators and the denominator is
// no greater than the number of successors.
assert((uint64_t)std::abs(Sum - BranchProbability::getDenominator()) <=
Probs.size() &&
"The sum of successors's probabilities exceeds one.");
#endif // NDEBUG
}
void MachineBasicBlock::addSuccessor(MachineBasicBlock *Succ,
BranchProbability Prob) {
// Probability list is either empty (if successor list isn't empty, this means
// disabled optimization) or has the same size as successor list.
if (!(Probs.empty() && !Successors.empty()))
Probs.push_back(Prob);
Successors.push_back(Succ);
Succ->addPredecessor(this);
}
void MachineBasicBlock::addSuccessorWithoutProb(MachineBasicBlock *Succ) {
// We need to make sure probability list is either empty or has the same size
// of successor list. When this function is called, we can safely delete all
// probability in the list.
Probs.clear();
Successors.push_back(Succ);
Succ->addPredecessor(this);
}
void MachineBasicBlock::removeSuccessor(MachineBasicBlock *Succ,
bool NormalizeSuccProbs) {
succ_iterator I = std::find(Successors.begin(), Successors.end(), Succ);
removeSuccessor(I, NormalizeSuccProbs);
}
MachineBasicBlock::succ_iterator
MachineBasicBlock::removeSuccessor(succ_iterator I, bool NormalizeSuccProbs) {
assert(I != Successors.end() && "Not a current successor!");
// If probability list is empty it means we don't use it (disabled
// optimization).
if (!Probs.empty()) {
probability_iterator WI = getProbabilityIterator(I);
Probs.erase(WI);
if (NormalizeSuccProbs)
normalizeSuccProbs();
}
(*I)->removePredecessor(this);
return Successors.erase(I);
}
void MachineBasicBlock::replaceSuccessor(MachineBasicBlock *Old,
MachineBasicBlock *New) {
if (Old == New)
return;
succ_iterator E = succ_end();
succ_iterator NewI = E;
succ_iterator OldI = E;
for (succ_iterator I = succ_begin(); I != E; ++I) {
if (*I == Old) {
OldI = I;
if (NewI != E)
break;
}
if (*I == New) {
NewI = I;
if (OldI != E)
break;
}
}
assert(OldI != E && "Old is not a successor of this block");
// If New isn't already a successor, let it take Old's place.
if (NewI == E) {
Old->removePredecessor(this);
New->addPredecessor(this);
*OldI = New;
return;
}
// New is already a successor.
// Update its probability instead of adding a duplicate edge.
if (!Probs.empty()) {
auto ProbIter = getProbabilityIterator(NewI);
if (!ProbIter->isUnknown())
*ProbIter += *getProbabilityIterator(OldI);
}
removeSuccessor(OldI);
}
void MachineBasicBlock::addPredecessor(MachineBasicBlock *Pred) {
Predecessors.push_back(Pred);
}
void MachineBasicBlock::removePredecessor(MachineBasicBlock *Pred) {
pred_iterator I = std::find(Predecessors.begin(), Predecessors.end(), Pred);
assert(I != Predecessors.end() && "Pred is not a predecessor of this block!");
Predecessors.erase(I);
}
void MachineBasicBlock::transferSuccessors(MachineBasicBlock *FromMBB) {
if (this == FromMBB)
return;
while (!FromMBB->succ_empty()) {
MachineBasicBlock *Succ = *FromMBB->succ_begin();
// If probability list is empty it means we don't use it (disabled optimization).
if (!FromMBB->Probs.empty()) {
auto Prob = *FromMBB->Probs.begin();
addSuccessor(Succ, Prob);
} else
addSuccessorWithoutProb(Succ);
FromMBB->removeSuccessor(Succ);
}
}
void
MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *FromMBB) {
if (this == FromMBB)
return;
while (!FromMBB->succ_empty()) {
MachineBasicBlock *Succ = *FromMBB->succ_begin();
if (!FromMBB->Probs.empty()) {
auto Prob = *FromMBB->Probs.begin();
addSuccessor(Succ, Prob);
} else
addSuccessorWithoutProb(Succ);
FromMBB->removeSuccessor(Succ);
// Fix up any PHI nodes in the successor.
for (MachineBasicBlock::instr_iterator MI = Succ->instr_begin(),
ME = Succ->instr_end(); MI != ME && MI->isPHI(); ++MI)
for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
MachineOperand &MO = MI->getOperand(i);
if (MO.getMBB() == FromMBB)
MO.setMBB(this);
}
}
normalizeSuccProbs();
}
bool MachineBasicBlock::isPredecessor(const MachineBasicBlock *MBB) const {
return std::find(pred_begin(), pred_end(), MBB) != pred_end();
}
bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
return std::find(succ_begin(), succ_end(), MBB) != succ_end();
}
bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
MachineFunction::const_iterator I(this);
return std::next(I) == MachineFunction::const_iterator(MBB);
}
bool MachineBasicBlock::canFallThrough() {
MachineFunction::iterator Fallthrough = getIterator();
++Fallthrough;
// If FallthroughBlock is off the end of the function, it can't fall through.
if (Fallthrough == getParent()->end())
return false;
// If FallthroughBlock isn't a successor, no fallthrough is possible.
if (!isSuccessor(&*Fallthrough))
return false;
// Analyze the branches, if any, at the end of the block.
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
const TargetInstrInfo *TII = getParent()->getSubtarget().getInstrInfo();
if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) {
// If we couldn't analyze the branch, examine the last instruction.
// If the block doesn't end in a known control barrier, assume fallthrough
// is possible. The isPredicated check is needed because this code can be
// called during IfConversion, where an instruction which is normally a
// Barrier is predicated and thus no longer an actual control barrier.
return empty() || !back().isBarrier() || TII->isPredicated(back());
}
// If there is no branch, control always falls through.
if (!TBB) return true;
// If there is some explicit branch to the fallthrough block, it can obviously
// reach, even though the branch should get folded to fall through implicitly.
if (MachineFunction::iterator(TBB) == Fallthrough ||
MachineFunction::iterator(FBB) == Fallthrough)
return true;
// If it's an unconditional branch to some block not the fall through, it
// doesn't fall through.
if (Cond.empty()) return false;
// Otherwise, if it is conditional and has no explicit false block, it falls
// through.
return FBB == nullptr;
}
MachineBasicBlock *MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ,
Pass &P) {
if (!canSplitCriticalEdge(Succ))
return nullptr;
MachineFunction *MF = getParent();
DebugLoc DL; // FIXME: this is nowhere
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
MF->insert(std::next(MachineFunction::iterator(this)), NMBB);
DEBUG(dbgs() << "Splitting critical edge:"
" BB#" << getNumber()
<< " -- BB#" << NMBB->getNumber()
<< " -- BB#" << Succ->getNumber() << '\n');
LiveIntervals *LIS = P.getAnalysisIfAvailable<LiveIntervals>();
SlotIndexes *Indexes = P.getAnalysisIfAvailable<SlotIndexes>();
if (LIS)
LIS->insertMBBInMaps(NMBB);
else if (Indexes)
Indexes->insertMBBInMaps(NMBB);
// On some targets like Mips, branches may kill virtual registers. Make sure
// that LiveVariables is properly updated after updateTerminator replaces the
// terminators.
LiveVariables *LV = P.getAnalysisIfAvailable<LiveVariables>();
// Collect a list of virtual registers killed by the terminators.
SmallVector<unsigned, 4> KilledRegs;
if (LV)
for (instr_iterator I = getFirstInstrTerminator(), E = instr_end();
I != E; ++I) {
MachineInstr *MI = &*I;
for (MachineInstr::mop_iterator OI = MI->operands_begin(),
OE = MI->operands_end(); OI != OE; ++OI) {
if (!OI->isReg() || OI->getReg() == 0 ||
!OI->isUse() || !OI->isKill() || OI->isUndef())
continue;
unsigned Reg = OI->getReg();
if (TargetRegisterInfo::isPhysicalRegister(Reg) ||
LV->getVarInfo(Reg).removeKill(MI)) {
KilledRegs.push_back(Reg);
DEBUG(dbgs() << "Removing terminator kill: " << *MI);
OI->setIsKill(false);
}
}
}
SmallVector<unsigned, 4> UsedRegs;
if (LIS) {
for (instr_iterator I = getFirstInstrTerminator(), E = instr_end();
I != E; ++I) {
MachineInstr *MI = &*I;
for (MachineInstr::mop_iterator OI = MI->operands_begin(),
OE = MI->operands_end(); OI != OE; ++OI) {
if (!OI->isReg() || OI->getReg() == 0)
continue;
unsigned Reg = OI->getReg();
if (std::find(UsedRegs.begin(), UsedRegs.end(), Reg) == UsedRegs.end())
UsedRegs.push_back(Reg);
}
}
}
ReplaceUsesOfBlockWith(Succ, NMBB);
// If updateTerminator() removes instructions, we need to remove them from
// SlotIndexes.
SmallVector<MachineInstr*, 4> Terminators;
if (Indexes) {
for (instr_iterator I = getFirstInstrTerminator(), E = instr_end();
I != E; ++I)
Terminators.push_back(&*I);
}
updateTerminator();
if (Indexes) {
SmallVector<MachineInstr*, 4> NewTerminators;
for (instr_iterator I = getFirstInstrTerminator(), E = instr_end();
I != E; ++I)
NewTerminators.push_back(&*I);
for (SmallVectorImpl<MachineInstr*>::iterator I = Terminators.begin(),
E = Terminators.end(); I != E; ++I) {
if (std::find(NewTerminators.begin(), NewTerminators.end(), *I) ==
NewTerminators.end())
Indexes->removeMachineInstrFromMaps(**I);
}
}
// Insert unconditional "jump Succ" instruction in NMBB if necessary.
NMBB->addSuccessor(Succ);
if (!NMBB->isLayoutSuccessor(Succ)) {
SmallVector<MachineOperand, 4> Cond;
const TargetInstrInfo *TII = getParent()->getSubtarget().getInstrInfo();
TII->InsertBranch(*NMBB, Succ, nullptr, Cond, DL);
if (Indexes) {
for (MachineInstr &MI : NMBB->instrs()) {
// Some instructions may have been moved to NMBB by updateTerminator(),
// so we first remove any instruction that already has an index.
if (Indexes->hasIndex(MI))
Indexes->removeMachineInstrFromMaps(MI);
Indexes->insertMachineInstrInMaps(MI);
}
}
}
// Fix PHI nodes in Succ so they refer to NMBB instead of this
for (MachineBasicBlock::instr_iterator
i = Succ->instr_begin(),e = Succ->instr_end();
i != e && i->isPHI(); ++i)
for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
if (i->getOperand(ni+1).getMBB() == this)
i->getOperand(ni+1).setMBB(NMBB);
// Inherit live-ins from the successor
for (const auto &LI : Succ->liveins())
NMBB->addLiveIn(LI);
// Update LiveVariables.
const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
if (LV) {
// Restore kills of virtual registers that were killed by the terminators.
while (!KilledRegs.empty()) {
unsigned Reg = KilledRegs.pop_back_val();
for (instr_iterator I = instr_end(), E = instr_begin(); I != E;) {
if (!(--I)->addRegisterKilled(Reg, TRI, /* addIfNotFound= */ false))
continue;
if (TargetRegisterInfo::isVirtualRegister(Reg))
LV->getVarInfo(Reg).Kills.push_back(&*I);
DEBUG(dbgs() << "Restored terminator kill: " << *I);
break;
}
}
// Update relevant live-through information.
LV->addNewBlock(NMBB, this, Succ);
}
if (LIS) {
// After splitting the edge and updating SlotIndexes, live intervals may be
// in one of two situations, depending on whether this block was the last in
// the function. If the original block was the last in the function, all
// live intervals will end prior to the beginning of the new split block. If
// the original block was not at the end of the function, all live intervals
// will extend to the end of the new split block.
bool isLastMBB =
std::next(MachineFunction::iterator(NMBB)) == getParent()->end();
SlotIndex StartIndex = Indexes->getMBBEndIdx(this);
SlotIndex PrevIndex = StartIndex.getPrevSlot();
SlotIndex EndIndex = Indexes->getMBBEndIdx(NMBB);
// Find the registers used from NMBB in PHIs in Succ.
SmallSet<unsigned, 8> PHISrcRegs;
for (MachineBasicBlock::instr_iterator
I = Succ->instr_begin(), E = Succ->instr_end();
I != E && I->isPHI(); ++I) {
for (unsigned ni = 1, ne = I->getNumOperands(); ni != ne; ni += 2) {
if (I->getOperand(ni+1).getMBB() == NMBB) {
MachineOperand &MO = I->getOperand(ni);
unsigned Reg = MO.getReg();
PHISrcRegs.insert(Reg);
if (MO.isUndef())
continue;
LiveInterval &LI = LIS->getInterval(Reg);
VNInfo *VNI = LI.getVNInfoAt(PrevIndex);
assert(VNI &&
"PHI sources should be live out of their predecessors.");
LI.addSegment(LiveInterval::Segment(StartIndex, EndIndex, VNI));
}
}
}
MachineRegisterInfo *MRI = &getParent()->getRegInfo();
for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
if (PHISrcRegs.count(Reg) || !LIS->hasInterval(Reg))
continue;
LiveInterval &LI = LIS->getInterval(Reg);
if (!LI.liveAt(PrevIndex))
continue;
bool isLiveOut = LI.liveAt(LIS->getMBBStartIdx(Succ));
if (isLiveOut && isLastMBB) {
VNInfo *VNI = LI.getVNInfoAt(PrevIndex);
assert(VNI && "LiveInterval should have VNInfo where it is live.");
LI.addSegment(LiveInterval::Segment(StartIndex, EndIndex, VNI));
} else if (!isLiveOut && !isLastMBB) {
LI.removeSegment(StartIndex, EndIndex);
}
}
// Update all intervals for registers whose uses may have been modified by
// updateTerminator().
LIS->repairIntervalsInRange(this, getFirstTerminator(), end(), UsedRegs);
}
if (MachineDominatorTree *MDT =
P.getAnalysisIfAvailable<MachineDominatorTree>())
MDT->recordSplitCriticalEdge(this, Succ, NMBB);
if (MachineLoopInfo *MLI = P.getAnalysisIfAvailable<MachineLoopInfo>())
if (MachineLoop *TIL = MLI->getLoopFor(this)) {
// If one or the other blocks were not in a loop, the new block is not
// either, and thus LI doesn't need to be updated.
if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
if (TIL == DestLoop) {
// Both in the same loop, the NMBB joins loop.
DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
} else if (TIL->contains(DestLoop)) {
// Edge from an outer loop to an inner loop. Add to the outer loop.
TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
} else if (DestLoop->contains(TIL)) {
// Edge from an inner loop to an outer loop. Add to the outer loop.
DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
} else {
// Edge from two loops with no containment relation. Because these
// are natural loops, we know that the destination block must be the
// header of its loop (adding a branch into a loop elsewhere would
// create an irreducible loop).
assert(DestLoop->getHeader() == Succ &&
"Should not create irreducible loops!");
if (MachineLoop *P = DestLoop->getParentLoop())
P->addBasicBlockToLoop(NMBB, MLI->getBase());
}
}
}
return NMBB;
}
bool MachineBasicBlock::canSplitCriticalEdge(
const MachineBasicBlock *Succ) const {
// Splitting the critical edge to a landing pad block is non-trivial. Don't do
// it in this generic function.
if (Succ->isEHPad())
return false;
const MachineFunction *MF = getParent();
// Performance might be harmed on HW that implements branching using exec mask
// where both sides of the branches are always executed.
if (MF->getTarget().requiresStructuredCFG())
return false;
// We may need to update this's terminator, but we can't do that if
// AnalyzeBranch fails. If this uses a jump table, we won't touch it.
const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
// AnalyzeBanch should modify this, since we did not allow modification.
if (TII->AnalyzeBranch(*const_cast<MachineBasicBlock *>(this), TBB, FBB, Cond,
/*AllowModify*/ false))
return false;
// Avoid bugpoint weirdness: A block may end with a conditional branch but
// jumps to the same MBB is either case. We have duplicate CFG edges in that
// case that we can't handle. Since this never happens in properly optimized
// code, just skip those edges.
if (TBB && TBB == FBB) {
DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
<< getNumber() << '\n');
return false;
}
return true;
}
/// Prepare MI to be removed from its bundle. This fixes bundle flags on MI's
/// neighboring instructions so the bundle won't be broken by removing MI.
static void unbundleSingleMI(MachineInstr *MI) {
// Removing the first instruction in a bundle.
if (MI->isBundledWithSucc() && !MI->isBundledWithPred())
MI->unbundleFromSucc();
// Removing the last instruction in a bundle.
if (MI->isBundledWithPred() && !MI->isBundledWithSucc())
MI->unbundleFromPred();
// If MI is not bundled, or if it is internal to a bundle, the neighbor flags
// are already fine.
}
MachineBasicBlock::instr_iterator
MachineBasicBlock::erase(MachineBasicBlock::instr_iterator I) {
unbundleSingleMI(&*I);
return Insts.erase(I);
}
MachineInstr *MachineBasicBlock::remove_instr(MachineInstr *MI) {
unbundleSingleMI(MI);
MI->clearFlag(MachineInstr::BundledPred);
MI->clearFlag(MachineInstr::BundledSucc);
return Insts.remove(MI);
}
MachineBasicBlock::instr_iterator
MachineBasicBlock::insert(instr_iterator I, MachineInstr *MI) {
assert(!MI->isBundledWithPred() && !MI->isBundledWithSucc() &&
"Cannot insert instruction with bundle flags");
// Set the bundle flags when inserting inside a bundle.
if (I != instr_end() && I->isBundledWithPred()) {
MI->setFlag(MachineInstr::BundledPred);
MI->setFlag(MachineInstr::BundledSucc);
}
return Insts.insert(I, MI);
}
/// This method unlinks 'this' from the containing function, and returns it, but
/// does not delete it.
MachineBasicBlock *MachineBasicBlock::removeFromParent() {
assert(getParent() && "Not embedded in a function!");
getParent()->remove(this);
return this;
}
/// This method unlinks 'this' from the containing function, and deletes it.
void MachineBasicBlock::eraseFromParent() {
assert(getParent() && "Not embedded in a function!");
getParent()->erase(this);
}
/// Given a machine basic block that branched to 'Old', change the code and CFG
/// so that it branches to 'New' instead.
void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
MachineBasicBlock *New) {
assert(Old != New && "Cannot replace self with self!");
MachineBasicBlock::instr_iterator I = instr_end();
while (I != instr_begin()) {
--I;
if (!I->isTerminator()) break;
// Scan the operands of this machine instruction, replacing any uses of Old
// with New.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (I->getOperand(i).isMBB() &&
I->getOperand(i).getMBB() == Old)
I->getOperand(i).setMBB(New);
}
// Update the successor information.
replaceSuccessor(Old, New);
}
/// Various pieces of code can cause excess edges in the CFG to be inserted. If
/// we have proven that MBB can only branch to DestA and DestB, remove any other
/// MBB successors from the CFG. DestA and DestB can be null.
///
/// Besides DestA and DestB, retain other edges leading to LandingPads
/// (currently there can be only one; we don't check or require that here).
/// Note it is possible that DestA and/or DestB are LandingPads.
bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
MachineBasicBlock *DestB,
bool IsCond) {
// The values of DestA and DestB frequently come from a call to the
// 'TargetInstrInfo::AnalyzeBranch' method. We take our meaning of the initial
// values from there.
//
// 1. If both DestA and DestB are null, then the block ends with no branches
// (it falls through to its successor).
// 2. If DestA is set, DestB is null, and IsCond is false, then the block ends
// with only an unconditional branch.
// 3. If DestA is set, DestB is null, and IsCond is true, then the block ends
// with a conditional branch that falls through to a successor (DestB).
// 4. If DestA and DestB is set and IsCond is true, then the block ends with a
// conditional branch followed by an unconditional branch. DestA is the
// 'true' destination and DestB is the 'false' destination.
bool Changed = false;
MachineFunction::iterator FallThru = std::next(getIterator());
if (!DestA && !DestB) {
// Block falls through to successor.
DestA = &*FallThru;
DestB = &*FallThru;
} else if (DestA && !DestB) {
if (IsCond)
// Block ends in conditional jump that falls through to successor.
DestB = &*FallThru;
} else {
assert(DestA && DestB && IsCond &&
"CFG in a bad state. Cannot correct CFG edges");
}
// Remove superfluous edges. I.e., those which aren't destinations of this
// basic block, duplicate edges, or landing pads.
SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
MachineBasicBlock::succ_iterator SI = succ_begin();
while (SI != succ_end()) {
const MachineBasicBlock *MBB = *SI;
if (!SeenMBBs.insert(MBB).second ||
(MBB != DestA && MBB != DestB && !MBB->isEHPad())) {
// This is a superfluous edge, remove it.
SI = removeSuccessor(SI);
Changed = true;
} else {
++SI;
}
}
if (Changed)
normalizeSuccProbs();
return Changed;
}
/// Find the next valid DebugLoc starting at MBBI, skipping any DBG_VALUE
/// instructions. Return UnknownLoc if there is none.
DebugLoc
MachineBasicBlock::findDebugLoc(instr_iterator MBBI) {
DebugLoc DL;
instr_iterator E = instr_end();
if (MBBI == E)
return DL;
// Skip debug declarations, we don't want a DebugLoc from them.
while (MBBI != E && MBBI->isDebugValue())
MBBI++;
if (MBBI != E)
DL = MBBI->getDebugLoc();
return DL;
}
/// Return probability of the edge from this block to MBB.
BranchProbability
MachineBasicBlock::getSuccProbability(const_succ_iterator Succ) const {
if (Probs.empty())
return BranchProbability(1, succ_size());
const auto &Prob = *getProbabilityIterator(Succ);
if (Prob.isUnknown()) {
// For unknown probabilities, collect the sum of all known ones, and evenly
// ditribute the complemental of the sum to each unknown probability.
unsigned KnownProbNum = 0;
auto Sum = BranchProbability::getZero();
for (auto &P : Probs) {
if (!P.isUnknown()) {
Sum += P;
KnownProbNum++;
}
}
return Sum.getCompl() / (Probs.size() - KnownProbNum);
} else
return Prob;
}
/// Set successor probability of a given iterator.
void MachineBasicBlock::setSuccProbability(succ_iterator I,
BranchProbability Prob) {
assert(!Prob.isUnknown());
if (Probs.empty())
return;
*getProbabilityIterator(I) = Prob;
}
/// Return probability iterator corresonding to the I successor iterator
MachineBasicBlock::const_probability_iterator
MachineBasicBlock::getProbabilityIterator(
MachineBasicBlock::const_succ_iterator I) const {
assert(Probs.size() == Successors.size() && "Async probability list!");
const size_t index = std::distance(Successors.begin(), I);
assert(index < Probs.size() && "Not a current successor!");
return Probs.begin() + index;
}
/// Return probability iterator corresonding to the I successor iterator.
MachineBasicBlock::probability_iterator
MachineBasicBlock::getProbabilityIterator(MachineBasicBlock::succ_iterator I) {
assert(Probs.size() == Successors.size() && "Async probability list!");
const size_t index = std::distance(Successors.begin(), I);
assert(index < Probs.size() && "Not a current successor!");
return Probs.begin() + index;
}
/// Return whether (physical) register "Reg" has been <def>ined and not <kill>ed
/// as of just before "MI".
///
/// Search is localised to a neighborhood of
/// Neighborhood instructions before (searching for defs or kills) and N
/// instructions after (searching just for defs) MI.
MachineBasicBlock::LivenessQueryResult
MachineBasicBlock::computeRegisterLiveness(const TargetRegisterInfo *TRI,
unsigned Reg, const_iterator Before,
unsigned Neighborhood) const {
unsigned N = Neighborhood;
// Start by searching backwards from Before, looking for kills, reads or defs.
const_iterator I(Before);
// If this is the first insn in the block, don't search backwards.
if (I != begin()) {
do {
--I;
MachineOperandIteratorBase::PhysRegInfo Info =
ConstMIOperands(*I).analyzePhysReg(Reg, TRI);
// Defs happen after uses so they take precedence if both are present.
// Register is dead after a dead def of the full register.
if (Info.DeadDef)
return LQR_Dead;
// Register is (at least partially) live after a def.
if (Info.Defined) {
if (!Info.PartialDeadDef)
return LQR_Live;
// As soon as we saw a partial definition (dead or not),
// we cannot tell if the value is partial live without
// tracking the lanemasks. We are not going to do this,
// so fall back on the remaining of the analysis.
break;
}
// Register is dead after a full kill or clobber and no def.
if (Info.Killed || Info.Clobbered)
return LQR_Dead;
// Register must be live if we read it.
if (Info.Read)
return LQR_Live;
} while (I != begin() && --N > 0);
}
// Did we get to the start of the block?
if (I == begin()) {
// If so, the register's state is definitely defined by the live-in state.
for (MCRegAliasIterator RAI(Reg, TRI, /*IncludeSelf=*/true); RAI.isValid();
++RAI)
if (isLiveIn(*RAI))
return LQR_Live;
return LQR_Dead;
}
N = Neighborhood;
// Try searching forwards from Before, looking for reads or defs.
I = const_iterator(Before);
// If this is the last insn in the block, don't search forwards.
if (I != end()) {
for (++I; I != end() && N > 0; ++I, --N) {
MachineOperandIteratorBase::PhysRegInfo Info =
ConstMIOperands(*I).analyzePhysReg(Reg, TRI);
// Register is live when we read it here.
if (Info.Read)
return LQR_Live;
// Register is dead if we can fully overwrite or clobber it here.
if (Info.FullyDefined || Info.Clobbered)
return LQR_Dead;
}
}
// At this point we have no idea of the liveness of the register.
return LQR_Unknown;
}
const uint32_t *
MachineBasicBlock::getBeginClobberMask(const TargetRegisterInfo *TRI) const {
// EH funclet entry does not preserve any registers.
return isEHFuncletEntry() ? TRI->getNoPreservedMask() : nullptr;
}
const uint32_t *
MachineBasicBlock::getEndClobberMask(const TargetRegisterInfo *TRI) const {
// If we see a return block with successors, this must be a funclet return,
// which does not preserve any registers. If there are no successors, we don't
// care what kind of return it is, putting a mask after it is a no-op.
return isReturnBlock() && !succ_empty() ? TRI->getNoPreservedMask() : nullptr;
}
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