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

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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/BasicBlock.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetInstrDesc.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/LeakDetector.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
: BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
AddressTaken(false) {
Insts.Parent = this;
}
MachineBasicBlock::~MachineBasicBlock() {
LeakDetector::removeGarbageObject(this);
}
/// getSymbol - Return the MCSymbol for this basic block.
///
MCSymbol *MachineBasicBlock::getSymbol() const {
const MachineFunction *MF = getParent();
MCContext &Ctx = MF->getContext();
const char *Prefix = Ctx.getAsmInfo().getPrivateGlobalPrefix();
return Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
Twine(MF->getFunctionNumber()) + "_" +
Twine(getNumber()));
}
raw_ostream &llvm::operator<<(raw_ostream &OS, const MachineBasicBlock &MBB) {
MBB.print(OS);
return OS;
}
/// addNodeToList (MBB) - 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::iterator I = N->begin(), E = N->end(); I != E; ++I)
I->AddRegOperandsToUseLists(RegInfo);
LeakDetector::removeGarbageObject(N);
}
void ilist_traits<MachineBasicBlock>::removeNodeFromList(MachineBasicBlock *N) {
N->getParent()->removeFromMBBNumbering(N->Number);
N->Number = -1;
LeakDetector::addGarbageObject(N);
}
/// addNodeToList (MI) - 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() == 0 && "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());
LeakDetector::removeGarbageObject(N);
}
/// removeNodeFromList (MI) - 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() != 0 && "machine instruction not in a basic block");
// Remove from the use/def lists.
N->RemoveRegOperandsFromUseLists();
N->setParent(0);
LeakDetector::addGarbageObject(N);
}
/// transferNodesFromList (MI) - 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,
MachineBasicBlock::iterator first,
MachineBasicBlock::iterator 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() {
iterator I = begin();
while (I != end() && I->isPHI())
++I;
return I;
}
MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
iterator I = end();
while (I != begin() && (--I)->getDesc().isTerminator())
; /*noop */
if (I != end() && !I->getDesc().isTerminator()) ++I;
return I;
}
void MachineBasicBlock::dump() const {
print(dbgs());
}
static inline void OutputReg(raw_ostream &os, unsigned RegNo,
const TargetRegisterInfo *TRI = 0) {
if (RegNo != 0 && TargetRegisterInfo::isPhysicalRegister(RegNo)) {
if (TRI)
os << " %" << TRI->get(RegNo).Name;
else
os << " %physreg" << RegNo;
} else
os << " %reg" << RegNo;
}
StringRef MachineBasicBlock::getName() const {
if (const BasicBlock *LBB = getBasicBlock())
return LBB->getName();
else
return "(null)";
}
void MachineBasicBlock::print(raw_ostream &OS) const {
const MachineFunction *MF = getParent();
if (!MF) {
OS << "Can't print out MachineBasicBlock because parent MachineFunction"
<< " is null\n";
return;
}
if (Alignment) { OS << "Alignment " << Alignment << "\n"; }
OS << "BB#" << getNumber() << ": ";
const char *Comma = "";
if (const BasicBlock *LBB = getBasicBlock()) {
OS << Comma << "derived from LLVM BB ";
WriteAsOperand(OS, LBB, /*PrintType=*/false);
Comma = ", ";
}
if (isLandingPad()) { OS << Comma << "EH LANDING PAD"; Comma = ", "; }
if (hasAddressTaken()) { OS << Comma << "ADDRESS TAKEN"; Comma = ", "; }
OS << '\n';
const TargetRegisterInfo *TRI = MF->getTarget().getRegisterInfo();
if (!livein_empty()) {
OS << " Live Ins:";
for (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
OutputReg(OS, *I, TRI);
OS << '\n';
}
// Print the preds of this block according to the CFG.
if (!pred_empty()) {
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 (const_iterator I = begin(); I != end(); ++I) {
OS << '\t';
I->print(OS, &getParent()->getTarget());
}
// Print the successors of this block according to the CFG.
if (!succ_empty()) {
OS << " Successors according to CFG:";
for (const_succ_iterator SI = succ_begin(), E = succ_end(); SI != E; ++SI)
OS << " BB#" << (*SI)->getNumber();
OS << '\n';
}
}
void MachineBasicBlock::removeLiveIn(unsigned Reg) {
std::vector<unsigned>::iterator I =
std::find(LiveIns.begin(), LiveIns.end(), Reg);
assert(I != LiveIns.end() && "Not a live in!");
LiveIns.erase(I);
}
bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
return I != livein_end();
}
void MachineBasicBlock::moveBefore(MachineBasicBlock *NewAfter) {
getParent()->splice(NewAfter, this);
}
void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
MachineFunction::iterator BBI = NewBefore;
getParent()->splice(++BBI, this);
}
void MachineBasicBlock::updateTerminator() {
const TargetInstrInfo *TII = getParent()->getTarget().getInstrInfo();
// A block with no successors has no concerns with fall-through edges.
if (this->succ_empty()) return;
MachineBasicBlock *TBB = 0, *FBB = 0;
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.
TBB = *succ_begin();
if (!isLayoutSuccessor(TBB))
TII->InsertBranch(*this, TBB, 0, 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, 0, Cond, dl);
} else if (isLayoutSuccessor(FBB)) {
TII->RemoveBranch(*this);
TII->InsertBranch(*this, TBB, 0, Cond, dl);
}
} else {
// The block has a fallthrough conditional branch.
MachineBasicBlock *MBBA = *succ_begin();
MachineBasicBlock *MBBB = *llvm::next(succ_begin());
if (MBBA == TBB) std::swap(MBBB, MBBA);
if (isLayoutSuccessor(TBB)) {
if (TII->ReverseBranchCondition(Cond)) {
// We can't reverse the condition, add an unconditional branch.
Cond.clear();
TII->InsertBranch(*this, MBBA, 0, Cond, dl);
return;
}
TII->RemoveBranch(*this);
TII->InsertBranch(*this, MBBA, 0, Cond, dl);
} else if (!isLayoutSuccessor(MBBA)) {
TII->RemoveBranch(*this);
TII->InsertBranch(*this, TBB, MBBA, Cond, dl);
}
}
}
}
void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ) {
Successors.push_back(succ);
succ->addPredecessor(this);
}
void MachineBasicBlock::removeSuccessor(MachineBasicBlock *succ) {
succ->removePredecessor(this);
succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
assert(I != Successors.end() && "Not a current successor!");
Successors.erase(I);
}
MachineBasicBlock::succ_iterator
MachineBasicBlock::removeSuccessor(succ_iterator I) {
assert(I != Successors.end() && "Not a current successor!");
(*I)->removePredecessor(this);
return Successors.erase(I);
}
void MachineBasicBlock::addPredecessor(MachineBasicBlock *pred) {
Predecessors.push_back(pred);
}
void MachineBasicBlock::removePredecessor(MachineBasicBlock *pred) {
std::vector<MachineBasicBlock *>::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();
addSuccessor(Succ);
fromMBB->removeSuccessor(Succ);
}
}
void
MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
if (this == fromMBB)
return;
while (!fromMBB->succ_empty()) {
MachineBasicBlock *Succ = *fromMBB->succ_begin();
addSuccessor(Succ);
fromMBB->removeSuccessor(Succ);
// Fix up any PHI nodes in the successor.
for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->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);
}
}
}
bool MachineBasicBlock::isSuccessor(const MachineBasicBlock *MBB) const {
std::vector<MachineBasicBlock *>::const_iterator I =
std::find(Successors.begin(), Successors.end(), MBB);
return I != Successors.end();
}
bool MachineBasicBlock::isLayoutSuccessor(const MachineBasicBlock *MBB) const {
MachineFunction::const_iterator I(this);
return llvm::next(I) == MachineFunction::const_iterator(MBB);
}
bool MachineBasicBlock::canFallThrough() {
MachineFunction::iterator Fallthrough = this;
++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 = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
const TargetInstrInfo *TII = getParent()->getTarget().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 isPredicable 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. This
// is over-conservative though, because if an instruction isn't actually
// predicated we could still treat it like a barrier.
return empty() || !back().getDesc().isBarrier() ||
back().getDesc().isPredicable();
}
// If there is no branch, control always falls through.
if (TBB == 0) 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 == 0;
}
MachineBasicBlock *
MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
MachineFunction *MF = getParent();
DebugLoc dl; // FIXME: this is nowhere
// 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->getTarget().getInstrInfo();
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
return NULL;
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
DEBUG(dbgs() << "PHIElimination splitting critical edge:"
" BB#" << getNumber()
<< " -- BB#" << NMBB->getNumber()
<< " -- BB#" << Succ->getNumber() << '\n');
ReplaceUsesOfBlockWith(Succ, NMBB);
updateTerminator();
// Insert unconditional "jump Succ" instruction in NMBB if necessary.
NMBB->addSuccessor(Succ);
if (!NMBB->isLayoutSuccessor(Succ)) {
Cond.clear();
MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
}
// Fix PHI nodes in Succ so they refer to NMBB instead of this
for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->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);
if (LiveVariables *LV =
P->getAnalysisIfAvailable<LiveVariables>())
LV->addNewBlock(NMBB, this, Succ);
if (MachineDominatorTree *MDT =
P->getAnalysisIfAvailable<MachineDominatorTree>())
MDT->addNewBlock(NMBB, this);
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;
}
/// removeFromParent - 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;
}
/// eraseFromParent - This method unlinks 'this' from the containing function,
/// and deletes it.
void MachineBasicBlock::eraseFromParent() {
assert(getParent() && "Not embedded in a function!");
getParent()->erase(this);
}
/// ReplaceUsesOfBlockWith - 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::iterator I = end();
while (I != begin()) {
--I;
if (!I->getDesc().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.
removeSuccessor(Old);
addSuccessor(New);
}
/// CorrectExtraCFGEdges - 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 =
llvm::next(MachineFunction::iterator(this));
if (DestA == 0 && DestB == 0) {
// Block falls through to successor.
DestA = FallThru;
DestB = FallThru;
} else if (DestA != 0 && DestB == 0) {
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) ||
(MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
// This is a superfluous edge, remove it.
SI = removeSuccessor(SI);
Changed = true;
} else {
++SI;
}
}
return Changed;
}
/// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping
/// any DBG_VALUE instructions. Return UnknownLoc if there is none.
DebugLoc
MachineBasicBlock::findDebugLoc(MachineBasicBlock::iterator &MBBI) {
DebugLoc DL;
MachineBasicBlock::iterator E = end();
if (MBBI != E) {
// Skip debug declarations, we don't want a DebugLoc from them.
MachineBasicBlock::iterator MBBI2 = MBBI;
while (MBBI2 != E && MBBI2->isDebugValue())
MBBI2++;
if (MBBI2 != E)
DL = MBBI2->getDebugLoc();
}
return DL;
}
void llvm::WriteAsOperand(raw_ostream &OS, const MachineBasicBlock *MBB,
bool t) {
OS << "BB#" << MBB->getNumber();
}
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