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llvm/lib/CodeGen/MachineBasicBlock.cpp
Quentin Colombet 49128636b6 [MachineDominatorTree] Provide a method to inform a MachineDominatorTree that a 
critical edge has been split. The MachineDominatorTree will when lazy update the
underlying dominance properties when require.

** Context **

This is a follow-up of r215410.
Each time a critical edge is split this invalidates the dominator tree
information. Thus, subsequent queries of that interface will be slow until the
underlying information is actually recomputed (costly).

** Problem **

Prior to this patch, splitting a critical edge needed to query the dominator
tree to update the dominator information.
Therefore, splitting a bunch of critical edges will likely produce poor
performance as each query to the dominator tree will use the slow query path.
This happens a lot in passes like MachineSink and PHIElimination.

** Proposed Solution **

Splitting a critical edge is a local modification of the CFG. Moreover, as soon
as a critical edge is split, it is not critical anymore and thus cannot be a
candidate for critical edge splitting anymore. In other words, the predecessor
and successor of a basic block inserted on a critical edge cannot be inserted by
critical edge splitting.

Using these observations, we can pile up the splitting of critical edge and
apply then at once before updating the DT information.

The core of this patch moves the update of the MachineDominatorTree information
from MachineBasicBlock::SplitCriticalEdge to a lazy MachineDominatorTree.

** Performance **

Thanks to this patch, the motivating example compiles in 4- minutes instead of
6+ minutes. No test case added as the motivating example as nothing special but
being huge!

The binaries are strictly identical for all the llvm test-suite + SPECs with and
without this patch for both Os and O3.

Regarding compile time, I observed only noise, although on average I saw a
small improvement.

<rdar://problem/17894619>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215576 91177308-0d34-0410-b5e6-96231b3b80d8
2014-08-13 21:00:07 +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/ADT/SmallString.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/LeakDetector.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.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 *bb)
: BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
AddressTaken(false), CachedMCSymbol(nullptr) {
Insts.Parent = this;
}
MachineBasicBlock::~MachineBasicBlock() {
LeakDetector::removeGarbageObject(this);
}
/// getSymbol - Return the MCSymbol for this basic block.
///
MCSymbol *MachineBasicBlock::getSymbol() const {
if (!CachedMCSymbol) {
const MachineFunction *MF = getParent();
MCContext &Ctx = MF->getContext();
const TargetMachine &TM = MF->getTarget();
const char *Prefix =
TM.getSubtargetImpl()->getDataLayout()->getPrivateGlobalPrefix();
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;
}
/// 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::instr_iterator
I = N->instr_begin(), E = N->instr_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() && "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() && "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);
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,
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::const_iterator
MachineBasicBlock::getFirstTerminator() const {
const_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::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();
}
MachineBasicBlock::const_iterator
MachineBasicBlock::getLastNonDebugInstr() const {
// Skip over end-of-block dbg_value instructions.
const_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();
}
const MachineBasicBlock *MachineBasicBlock::getLandingPadSuccessor() const {
// A block with a landing pad successor only has one other successor.
if (succ_size() > 2)
return nullptr;
for (const_succ_iterator I = succ_begin(), E = succ_end(); I != E; ++I)
if ((*I)->isLandingPad())
return *I;
return nullptr;
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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 += (Twine("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;
}
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);
Comma = ", ";
}
if (isLandingPad()) { 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 (livein_iterator I = livein_begin(),E = livein_end(); I != E; ++I)
OS << ' ' << PrintReg(*I, TRI);
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 (const_instr_iterator I = instr_begin(); I != instr_end(); ++I) {
if (Indexes) {
if (Indexes->hasIndex(I))
OS << Indexes->getInstructionIndex(I);
OS << '\t';
}
OS << '\t';
if (I->isInsideBundle())
OS << " * ";
I->print(OS, &getParent()->getTarget());
}
// 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 (!Weights.empty())
OS << '(' << *getWeightIterator(SI) << ')';
}
OS << '\n';
}
}
void MachineBasicBlock::printAsOperand(raw_ostream &OS, bool /*PrintType*/) const {
OS << "BB#" << getNumber();
}
void MachineBasicBlock::removeLiveIn(unsigned Reg) {
std::vector<unsigned>::iterator I =
std::find(LiveIns.begin(), LiveIns.end(), Reg);
if (I != LiveIns.end())
LiveIns.erase(I);
}
bool MachineBasicBlock::isLiveIn(unsigned Reg) const {
livein_iterator I = std::find(livein_begin(), livein_end(), Reg);
return I != livein_end();
}
unsigned
MachineBasicBlock::addLiveIn(unsigned 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((isLandingPad() || 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, this);
}
void MachineBasicBlock::moveAfter(MachineBasicBlock *NewBefore) {
MachineFunction::iterator BBI = NewBefore;
getParent()->splice(++BBI, this);
}
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)->isLandingPad())
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)->isLandingPad() || *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::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
// If we see non-zero value for the first time it means we actually use Weight
// list, so we fill all Weights with 0's.
if (weight != 0 && Weights.empty())
Weights.resize(Successors.size());
if (weight != 0 || !Weights.empty())
Weights.push_back(weight);
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!");
// If Weight list is empty it means we don't use it (disabled optimization).
if (!Weights.empty()) {
weight_iterator WI = getWeightIterator(I);
Weights.erase(WI);
}
Successors.erase(I);
}
MachineBasicBlock::succ_iterator
MachineBasicBlock::removeSuccessor(succ_iterator I) {
assert(I != Successors.end() && "Not a current successor!");
// If Weight list is empty it means we don't use it (disabled optimization).
if (!Weights.empty()) {
weight_iterator WI = getWeightIterator(I);
Weights.erase(WI);
}
(*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");
Old->removePredecessor(this);
// If New isn't already a successor, let it take Old's place.
if (NewI == E) {
New->addPredecessor(this);
*OldI = New;
return;
}
// New is already a successor.
// Update its weight instead of adding a duplicate edge.
if (!Weights.empty()) {
weight_iterator OldWI = getWeightIterator(OldI);
*getWeightIterator(NewI) += *OldWI;
Weights.erase(OldWI);
}
Successors.erase(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();
uint32_t Weight = 0;
// If Weight list is empty it means we don't use it (disabled optimization).
if (!fromMBB->Weights.empty())
Weight = *fromMBB->Weights.begin();
addSuccessor(Succ, Weight);
fromMBB->removeSuccessor(Succ);
}
}
void
MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *fromMBB) {
if (this == fromMBB)
return;
while (!fromMBB->succ_empty()) {
MachineBasicBlock *Succ = *fromMBB->succ_begin();
uint32_t Weight = 0;
if (!fromMBB->Weights.empty())
Weight = *fromMBB->Weights.begin();
addSuccessor(Succ, Weight);
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);
}
}
}
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 = 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 = 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) {
// Splitting the critical edge to a landing pad block is non-trivial. Don't do
// it in this generic function.
if (Succ->isLandingPad())
return nullptr;
MachineFunction *MF = getParent();
DebugLoc dl; // FIXME: this is nowhere
// 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 nullptr;
// 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;
if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
return nullptr;
// 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 nullptr;
}
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)) {
Cond.clear();
MF->getSubtarget().getInstrInfo()->InsertBranch(*NMBB, Succ, nullptr, Cond,
dl);
if (Indexes) {
for (instr_iterator I = NMBB->instr_begin(), E = NMBB->instr_end();
I != E; ++I) {
// Some instructions may have been moved to NMBB by updateTerminator(),
// so we first remove any instruction that already has an index.
if (Indexes->hasIndex(I))
Indexes->removeMachineInstrFromMaps(I);
Indexes->insertMachineInstrInMaps(I);
}
}
}
// 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 (MachineBasicBlock::livein_iterator I = Succ->livein_begin(),
E = Succ->livein_end(); I != E; ++I)
NMBB->addLiveIn(*I);
// 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;
}
/// 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);
}
/// 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::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);
}
/// 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 =
std::next(MachineFunction::iterator(this));
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) ||
(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(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;
}
/// getSuccWeight - Return weight of the edge from this block to MBB.
///
uint32_t MachineBasicBlock::getSuccWeight(const_succ_iterator Succ) const {
if (Weights.empty())
return 0;
return *getWeightIterator(Succ);
}
/// Set successor weight of a given iterator.
void MachineBasicBlock::setSuccWeight(succ_iterator I, uint32_t weight) {
if (Weights.empty())
return;
*getWeightIterator(I) = weight;
}
/// getWeightIterator - Return wight iterator corresonding to the I successor
/// iterator
MachineBasicBlock::weight_iterator MachineBasicBlock::
getWeightIterator(MachineBasicBlock::succ_iterator I) {
assert(Weights.size() == Successors.size() && "Async weight list!");
size_t index = std::distance(Successors.begin(), I);
assert(index < Weights.size() && "Not a current successor!");
return Weights.begin() + index;
}
/// getWeightIterator - Return wight iterator corresonding to the I successor
/// iterator
MachineBasicBlock::const_weight_iterator MachineBasicBlock::
getWeightIterator(MachineBasicBlock::const_succ_iterator I) const {
assert(Weights.size() == Successors.size() && "Async weight list!");
const size_t index = std::distance(Successors.begin(), I);
assert(index < Weights.size() && "Not a current successor!");
return Weights.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, MachineInstr *MI,
unsigned Neighborhood) {
unsigned N = Neighborhood;
MachineBasicBlock *MBB = MI->getParent();
// Start by searching backwards from MI, looking for kills, reads or defs.
MachineBasicBlock::iterator I(MI);
// If this is the first insn in the block, don't search backwards.
if (I != MBB->begin()) {
do {
--I;
MachineOperandIteratorBase::PhysRegInfo Analysis =
MIOperands(I).analyzePhysReg(Reg, TRI);
if (Analysis.Defines)
// Outputs happen after inputs so they take precedence if both are
// present.
return Analysis.DefinesDead ? LQR_Dead : LQR_Live;
if (Analysis.Kills || Analysis.Clobbers)
// Register killed, so isn't live.
return LQR_Dead;
else if (Analysis.ReadsOverlap)
// Defined or read without a previous kill - live.
return Analysis.Reads ? LQR_Live : LQR_OverlappingLive;
} while (I != MBB->begin() && --N > 0);
}
// Did we get to the start of the block?
if (I == MBB->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 (MBB->isLiveIn(*RAI))
return (*RAI == Reg) ? LQR_Live : LQR_OverlappingLive;
}
return LQR_Dead;
}
N = Neighborhood;
// Try searching forwards from MI, looking for reads or defs.
I = MachineBasicBlock::iterator(MI);
// If this is the last insn in the block, don't search forwards.
if (I != MBB->end()) {
for (++I; I != MBB->end() && N > 0; ++I, --N) {
MachineOperandIteratorBase::PhysRegInfo Analysis =
MIOperands(I).analyzePhysReg(Reg, TRI);
if (Analysis.ReadsOverlap)
// Used, therefore must have been live.
return (Analysis.Reads) ?
LQR_Live : LQR_OverlappingLive;
else if (Analysis.Clobbers || Analysis.Defines)
// Defined (but not read) therefore cannot have been live.
return LQR_Dead;
}
}
// At this point we have no idea of the liveness of the register.
return LQR_Unknown;
}
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