//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "tailduplication"
-#include "llvm/Function.h"
#include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/MachineSSAUpdater.h"
-#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/IR/Function.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
-#include "llvm/ADT/SmallSet.h"
-#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/Statistic.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
+#define DEBUG_TYPE "tailduplication"
+
STATISTIC(NumTails , "Number of tails duplicated");
STATISTIC(NumTailDups , "Number of tail duplicated blocks");
STATISTIC(NumInstrDups , "Additional instructions due to tail duplication");
STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
+STATISTIC(NumAddedPHIs , "Number of phis added");
// Heuristic for tail duplication.
static cl::opt<unsigned>
typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy;
namespace {
- /// TailDuplicatePass - Perform tail duplication.
+ /// Perform tail duplication.
class TailDuplicatePass : public MachineFunctionPass {
- bool PreRegAlloc;
const TargetInstrInfo *TII;
+ const TargetRegisterInfo *TRI;
+ const MachineBranchProbabilityInfo *MBPI;
MachineModuleInfo *MMI;
MachineRegisterInfo *MRI;
+ std::unique_ptr<RegScavenger> RS;
+ bool PreRegAlloc;
- // SSAUpdateVRs - A list of virtual registers for which to update SSA form.
+ // A list of virtual registers for which to update SSA form.
SmallVector<unsigned, 16> SSAUpdateVRs;
- // SSAUpdateVals - For each virtual register in SSAUpdateVals keep a list of
- // source virtual registers.
+ // For each virtual register in SSAUpdateVals keep a list of source virtual
+ // registers.
DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;
public:
static char ID;
- explicit TailDuplicatePass(bool PreRA) :
- MachineFunctionPass(ID), PreRegAlloc(PreRA) {}
+ explicit TailDuplicatePass() :
+ MachineFunctionPass(ID), PreRegAlloc(false) {}
+
+ bool runOnMachineFunction(MachineFunction &MF) override;
- virtual bool runOnMachineFunction(MachineFunction &MF);
- virtual const char *getPassName() const { return "Tail Duplication"; }
+ void getAnalysisUsage(AnalysisUsage &AU) const override;
private:
void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
MachineBasicBlock *PredBB,
DenseMap<unsigned, unsigned> &LocalVRMap,
- SmallVector<std::pair<unsigned,unsigned>, 4> &Copies);
+ SmallVectorImpl<std::pair<unsigned,unsigned> > &Copies,
+ const DenseSet<unsigned> &UsedByPhi,
+ bool Remove);
void DuplicateInstruction(MachineInstr *MI,
MachineBasicBlock *TailBB,
MachineBasicBlock *PredBB,
MachineFunction &MF,
- DenseMap<unsigned, unsigned> &LocalVRMap);
+ DenseMap<unsigned, unsigned> &LocalVRMap,
+ const DenseSet<unsigned> &UsedByPhi);
void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
- SmallVector<MachineBasicBlock*, 8> &TDBBs,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
SmallSetVector<MachineBasicBlock*, 8> &Succs);
bool TailDuplicateBlocks(MachineFunction &MF);
- bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
- SmallVector<MachineBasicBlock*, 8> &TDBBs,
- SmallVector<MachineInstr*, 16> &Copies);
+ bool shouldTailDuplicate(const MachineFunction &MF,
+ bool IsSimple, MachineBasicBlock &TailBB);
+ bool isSimpleBB(MachineBasicBlock *TailBB);
+ bool canCompletelyDuplicateBB(MachineBasicBlock &BB);
+ bool duplicateSimpleBB(MachineBasicBlock *TailBB,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+ const DenseSet<unsigned> &RegsUsedByPhi,
+ SmallVectorImpl<MachineInstr *> &Copies);
+ bool TailDuplicate(MachineBasicBlock *TailBB,
+ bool IsSimple,
+ MachineFunction &MF,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+ SmallVectorImpl<MachineInstr *> &Copies);
+ bool TailDuplicateAndUpdate(MachineBasicBlock *MBB,
+ bool IsSimple,
+ MachineFunction &MF);
+
void RemoveDeadBlock(MachineBasicBlock *MBB);
};
char TailDuplicatePass::ID = 0;
}
-FunctionPass *llvm::createTailDuplicatePass(bool PreRegAlloc) {
- return new TailDuplicatePass(PreRegAlloc);
-}
+char &llvm::TailDuplicateID = TailDuplicatePass::ID;
+
+INITIALIZE_PASS(TailDuplicatePass, "tailduplication", "Tail Duplication",
+ false, false)
bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
- TII = MF.getTarget().getInstrInfo();
+ if (skipOptnoneFunction(*MF.getFunction()))
+ return false;
+
+ TII = MF.getSubtarget().getInstrInfo();
+ TRI = MF.getSubtarget().getRegisterInfo();
MRI = &MF.getRegInfo();
MMI = getAnalysisIfAvailable<MachineModuleInfo>();
+ MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
+
+ PreRegAlloc = MRI->isSSA();
+ RS.reset();
+ if (MRI->tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF))
+ RS.reset(new RegScavenger());
bool MadeChange = false;
while (TailDuplicateBlocks(MF))
return MadeChange;
}
+void TailDuplicatePass::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<MachineBranchProbabilityInfo>();
+ MachineFunctionPass::getAnalysisUsage(AU);
+}
+
static void VerifyPHIs(MachineFunction &MF, bool CheckExtra) {
for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ++I) {
- MachineBasicBlock *MBB = I;
+ MachineBasicBlock *MBB = &*I;
SmallSetVector<MachineBasicBlock*, 8> Preds(MBB->pred_begin(),
MBB->pred_end());
MachineBasicBlock::iterator MI = MBB->begin();
dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
dbgs() << " missing input from predecessor BB#"
<< PredBB->getNumber() << '\n';
- llvm_unreachable(0);
+ llvm_unreachable(nullptr);
}
}
for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
if (CheckExtra && !Preds.count(PHIBB)) {
- // This is not a hard error.
dbgs() << "Warning: malformed PHI in BB#" << MBB->getNumber()
<< ": " << *MI;
dbgs() << " extra input from predecessor BB#"
<< PHIBB->getNumber() << '\n';
+ llvm_unreachable(nullptr);
}
if (PHIBB->getNumber() < 0) {
dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
dbgs() << " non-existing BB#" << PHIBB->getNumber() << '\n';
- llvm_unreachable(0);
+ llvm_unreachable(nullptr);
}
}
++MI;
}
}
-/// TailDuplicateBlocks - Look for small blocks that are unconditionally
-/// branched to and do not fall through. Tail-duplicate their instructions
-/// into their predecessors to eliminate (dynamic) branches.
-bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
- bool MadeChange = false;
+/// Tail duplicate the block and cleanup.
+bool
+TailDuplicatePass::TailDuplicateAndUpdate(MachineBasicBlock *MBB,
+ bool IsSimple,
+ MachineFunction &MF) {
+ // Save the successors list.
+ SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
+ MBB->succ_end());
+
+ SmallVector<MachineBasicBlock*, 8> TDBBs;
+ SmallVector<MachineInstr*, 16> Copies;
+ if (!TailDuplicate(MBB, IsSimple, MF, TDBBs, Copies))
+ return false;
- if (PreRegAlloc && TailDupVerify) {
- DEBUG(dbgs() << "\n*** Before tail-duplicating\n");
- VerifyPHIs(MF, true);
- }
+ ++NumTails;
SmallVector<MachineInstr*, 8> NewPHIs;
MachineSSAUpdater SSAUpdate(MF, &NewPHIs);
- for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
- MachineBasicBlock *MBB = I++;
+ // TailBB's immediate successors are now successors of those predecessors
+ // which duplicated TailBB. Add the predecessors as sources to the PHI
+ // instructions.
+ bool isDead = MBB->pred_empty() && !MBB->hasAddressTaken();
+ if (PreRegAlloc)
+ UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
+
+ // If it is dead, remove it.
+ if (isDead) {
+ NumInstrDups -= MBB->size();
+ RemoveDeadBlock(MBB);
+ ++NumDeadBlocks;
+ }
- if (NumTails == TailDupLimit)
- break;
+ // Update SSA form.
+ if (!SSAUpdateVRs.empty()) {
+ for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
+ unsigned VReg = SSAUpdateVRs[i];
+ SSAUpdate.Initialize(VReg);
+
+ // If the original definition is still around, add it as an available
+ // value.
+ MachineInstr *DefMI = MRI->getVRegDef(VReg);
+ MachineBasicBlock *DefBB = nullptr;
+ if (DefMI) {
+ DefBB = DefMI->getParent();
+ SSAUpdate.AddAvailableValue(DefBB, VReg);
+ }
- // Only duplicate blocks that end with unconditional branches.
- if (MBB->canFallThrough())
- continue;
+ // Add the new vregs as available values.
+ DenseMap<unsigned, AvailableValsTy>::iterator LI =
+ SSAUpdateVals.find(VReg);
+ for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
+ MachineBasicBlock *SrcBB = LI->second[j].first;
+ unsigned SrcReg = LI->second[j].second;
+ SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
+ }
- // Save the successors list.
- SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
- MBB->succ_end());
+ // Rewrite uses that are outside of the original def's block.
+ MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
+ while (UI != MRI->use_end()) {
+ MachineOperand &UseMO = *UI;
+ MachineInstr *UseMI = UseMO.getParent();
+ ++UI;
+ if (UseMI->isDebugValue()) {
+ // SSAUpdate can replace the use with an undef. That creates
+ // a debug instruction that is a kill.
+ // FIXME: Should it SSAUpdate job to delete debug instructions
+ // instead of replacing the use with undef?
+ UseMI->eraseFromParent();
+ continue;
+ }
+ if (UseMI->getParent() == DefBB && !UseMI->isPHI())
+ continue;
+ SSAUpdate.RewriteUse(UseMO);
+ }
+ }
- SmallVector<MachineBasicBlock*, 8> TDBBs;
- SmallVector<MachineInstr*, 16> Copies;
- if (TailDuplicate(MBB, MF, TDBBs, Copies)) {
- ++NumTails;
+ SSAUpdateVRs.clear();
+ SSAUpdateVals.clear();
+ }
- // TailBB's immediate successors are now successors of those predecessors
- // which duplicated TailBB. Add the predecessors as sources to the PHI
- // instructions.
- bool isDead = MBB->pred_empty();
- if (PreRegAlloc)
- UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
+ // Eliminate some of the copies inserted by tail duplication to maintain
+ // SSA form.
+ for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
+ MachineInstr *Copy = Copies[i];
+ if (!Copy->isCopy())
+ continue;
+ unsigned Dst = Copy->getOperand(0).getReg();
+ unsigned Src = Copy->getOperand(1).getReg();
+ if (MRI->hasOneNonDBGUse(Src) &&
+ MRI->constrainRegClass(Src, MRI->getRegClass(Dst))) {
+ // Copy is the only use. Do trivial copy propagation here.
+ MRI->replaceRegWith(Dst, Src);
+ Copy->eraseFromParent();
+ }
+ }
- // If it is dead, remove it.
- if (isDead) {
- NumInstrDups -= MBB->size();
- RemoveDeadBlock(MBB);
- ++NumDeadBlocks;
- }
+ if (NewPHIs.size())
+ NumAddedPHIs += NewPHIs.size();
- // Update SSA form.
- if (!SSAUpdateVRs.empty()) {
- for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
- unsigned VReg = SSAUpdateVRs[i];
- SSAUpdate.Initialize(VReg);
-
- // If the original definition is still around, add it as an available
- // value.
- MachineInstr *DefMI = MRI->getVRegDef(VReg);
- MachineBasicBlock *DefBB = 0;
- if (DefMI) {
- DefBB = DefMI->getParent();
- SSAUpdate.AddAvailableValue(DefBB, VReg);
- }
+ return true;
+}
- // Add the new vregs as available values.
- DenseMap<unsigned, AvailableValsTy>::iterator LI =
- SSAUpdateVals.find(VReg);
- for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
- MachineBasicBlock *SrcBB = LI->second[j].first;
- unsigned SrcReg = LI->second[j].second;
- SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
- }
+/// Look for small blocks that are unconditionally branched to and do not fall
+/// through. Tail-duplicate their instructions into their predecessors to
+/// eliminate (dynamic) branches.
+bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
+ bool MadeChange = false;
- // Rewrite uses that are outside of the original def's block.
- MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
- while (UI != MRI->use_end()) {
- MachineOperand &UseMO = UI.getOperand();
- MachineInstr *UseMI = &*UI;
- ++UI;
- if (UseMI->getParent() == DefBB)
- continue;
- SSAUpdate.RewriteUse(UseMO);
- }
- }
+ if (PreRegAlloc && TailDupVerify) {
+ DEBUG(dbgs() << "\n*** Before tail-duplicating\n");
+ VerifyPHIs(MF, true);
+ }
- SSAUpdateVRs.clear();
- SSAUpdateVals.clear();
- }
+ for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
+ MachineBasicBlock *MBB = &*I++;
- // Eliminate some of the copies inserted by tail duplication to maintain
- // SSA form.
- for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
- MachineInstr *Copy = Copies[i];
- if (!Copy->isCopy())
- continue;
- unsigned Dst = Copy->getOperand(0).getReg();
- unsigned Src = Copy->getOperand(1).getReg();
- MachineRegisterInfo::use_iterator UI = MRI->use_begin(Src);
- if (++UI == MRI->use_end()) {
- // Copy is the only use. Do trivial copy propagation here.
- MRI->replaceRegWith(Dst, Src);
- Copy->eraseFromParent();
- }
- }
+ if (NumTails == TailDupLimit)
+ break;
- if (PreRegAlloc && TailDupVerify)
- VerifyPHIs(MF, false);
- MadeChange = true;
- }
+ bool IsSimple = isSimpleBB(MBB);
+
+ if (!shouldTailDuplicate(MF, IsSimple, *MBB))
+ continue;
+
+ MadeChange |= TailDuplicateAndUpdate(MBB, IsSimple, MF);
}
+ if (PreRegAlloc && TailDupVerify)
+ VerifyPHIs(MF, false);
+
return MadeChange;
}
static bool isDefLiveOut(unsigned Reg, MachineBasicBlock *BB,
const MachineRegisterInfo *MRI) {
- for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
- UE = MRI->use_end(); UI != UE; ++UI) {
- MachineInstr *UseMI = &*UI;
- if (UseMI->getParent() != BB)
+ for (MachineInstr &UseMI : MRI->use_instructions(Reg)) {
+ if (UseMI.isDebugValue())
+ continue;
+ if (UseMI.getParent() != BB)
return true;
}
return false;
return 0;
}
-/// AddSSAUpdateEntry - Add a definition and source virtual registers pair for
-/// SSA update.
+
+// Remember which registers are used by phis in this block. This is
+// used to determine which registers are liveout while modifying the
+// block (which is why we need to copy the information).
+static void getRegsUsedByPHIs(const MachineBasicBlock &BB,
+ DenseSet<unsigned> *UsedByPhi) {
+ for (const auto &MI : BB) {
+ if (!MI.isPHI())
+ break;
+ for (unsigned i = 1, e = MI.getNumOperands(); i != e; i += 2) {
+ unsigned SrcReg = MI.getOperand(i).getReg();
+ UsedByPhi->insert(SrcReg);
+ }
+ }
+}
+
+/// Add a definition and source virtual registers pair for SSA update.
void TailDuplicatePass::AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
MachineBasicBlock *BB) {
DenseMap<unsigned, AvailableValsTy>::iterator LI= SSAUpdateVals.find(OrigReg);
}
}
-/// ProcessPHI - Process PHI node in TailBB by turning it into a copy in PredBB.
-/// Remember the source register that's contributed by PredBB and update SSA
-/// update map.
-void TailDuplicatePass::ProcessPHI(MachineInstr *MI,
- MachineBasicBlock *TailBB,
- MachineBasicBlock *PredBB,
- DenseMap<unsigned, unsigned> &LocalVRMap,
- SmallVector<std::pair<unsigned,unsigned>, 4> &Copies) {
+/// Process PHI node in TailBB by turning it into a copy in PredBB. Remember the
+/// source register that's contributed by PredBB and update SSA update map.
+void TailDuplicatePass::ProcessPHI(
+ MachineInstr *MI, MachineBasicBlock *TailBB, MachineBasicBlock *PredBB,
+ DenseMap<unsigned, unsigned> &LocalVRMap,
+ SmallVectorImpl<std::pair<unsigned, unsigned> > &Copies,
+ const DenseSet<unsigned> &RegsUsedByPhi, bool Remove) {
unsigned DefReg = MI->getOperand(0).getReg();
unsigned SrcOpIdx = getPHISrcRegOpIdx(MI, PredBB);
assert(SrcOpIdx && "Unable to find matching PHI source?");
// available value liveout of the block.
unsigned NewDef = MRI->createVirtualRegister(RC);
Copies.push_back(std::make_pair(NewDef, SrcReg));
- if (isDefLiveOut(DefReg, TailBB, MRI))
+ if (isDefLiveOut(DefReg, TailBB, MRI) || RegsUsedByPhi.count(DefReg))
AddSSAUpdateEntry(DefReg, NewDef, PredBB);
+ if (!Remove)
+ return;
+
// Remove PredBB from the PHI node.
MI->RemoveOperand(SrcOpIdx+1);
MI->RemoveOperand(SrcOpIdx);
MI->eraseFromParent();
}
-/// DuplicateInstruction - Duplicate a TailBB instruction to PredBB and update
+/// Duplicate a TailBB instruction to PredBB and update
/// the source operands due to earlier PHI translation.
void TailDuplicatePass::DuplicateInstruction(MachineInstr *MI,
MachineBasicBlock *TailBB,
MachineBasicBlock *PredBB,
MachineFunction &MF,
- DenseMap<unsigned, unsigned> &LocalVRMap) {
+ DenseMap<unsigned, unsigned> &LocalVRMap,
+ const DenseSet<unsigned> &UsedByPhi) {
MachineInstr *NewMI = TII->duplicate(MI, MF);
for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = NewMI->getOperand(i);
unsigned NewReg = MRI->createVirtualRegister(RC);
MO.setReg(NewReg);
LocalVRMap.insert(std::make_pair(Reg, NewReg));
- if (isDefLiveOut(Reg, TailBB, MRI))
+ if (isDefLiveOut(Reg, TailBB, MRI) || UsedByPhi.count(Reg))
AddSSAUpdateEntry(Reg, NewReg, PredBB);
} else {
DenseMap<unsigned, unsigned>::iterator VI = LocalVRMap.find(Reg);
- if (VI != LocalVRMap.end())
+ if (VI != LocalVRMap.end()) {
MO.setReg(VI->second);
+ // Clear any kill flags from this operand. The new register could have
+ // uses after this one, so kills are not valid here.
+ MO.setIsKill(false);
+ MRI->constrainRegClass(VI->second, MRI->getRegClass(Reg));
+ }
}
}
- PredBB->insert(PredBB->end(), NewMI);
+ PredBB->insert(PredBB->instr_end(), NewMI);
}
-/// UpdateSuccessorsPHIs - After FromBB is tail duplicated into its predecessor
-/// blocks, the successors have gained new predecessors. Update the PHI
-/// instructions in them accordingly.
+/// After FromBB is tail duplicated into its predecessor blocks, the successors
+/// have gained new predecessors. Update the PHI instructions in them
+/// accordingly.
void
TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
- SmallVector<MachineBasicBlock*, 8> &TDBBs,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
SmallSetVector<MachineBasicBlock*,8> &Succs) {
for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(),
SE = Succs.end(); SI != SE; ++SI) {
II != EE; ++II) {
if (!II->isPHI())
break;
+ MachineInstrBuilder MIB(*FromBB->getParent(), II);
unsigned Idx = 0;
for (unsigned i = 1, e = II->getNumOperands(); i != e; i += 2) {
MachineOperand &MO = II->getOperand(i+1);
// This register is defined in the tail block.
for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
MachineBasicBlock *SrcBB = LI->second[j].first;
+ // If we didn't duplicate a bb into a particular predecessor, we
+ // might still have added an entry to SSAUpdateVals to correcly
+ // recompute SSA. If that case, avoid adding a dummy extra argument
+ // this PHI.
+ if (!SrcBB->isSuccessor(SuccBB))
+ continue;
+
unsigned SrcReg = LI->second[j].second;
if (Idx != 0) {
II->getOperand(Idx).setReg(SrcReg);
II->getOperand(Idx+1).setMBB(SrcBB);
Idx = 0;
} else {
- II->addOperand(MachineOperand::CreateReg(SrcReg, false));
- II->addOperand(MachineOperand::CreateMBB(SrcBB));
+ MIB.addReg(SrcReg).addMBB(SrcBB);
}
}
} else {
II->getOperand(Idx+1).setMBB(SrcBB);
Idx = 0;
} else {
- II->addOperand(MachineOperand::CreateReg(Reg, false));
- II->addOperand(MachineOperand::CreateMBB(SrcBB));
+ MIB.addReg(Reg).addMBB(SrcBB);
}
}
}
}
}
-/// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
-/// of its predecessors.
+/// Determine if it is profitable to duplicate this block.
bool
-TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
- SmallVector<MachineBasicBlock*, 8> &TDBBs,
- SmallVector<MachineInstr*, 16> &Copies) {
- // Set the limit on the number of instructions to duplicate, with a default
- // of one less than the tail-merge threshold. When optimizing for size,
+TailDuplicatePass::shouldTailDuplicate(const MachineFunction &MF,
+ bool IsSimple,
+ MachineBasicBlock &TailBB) {
+ // Only duplicate blocks that end with unconditional branches.
+ if (TailBB.canFallThrough())
+ return false;
+
+ // Don't try to tail-duplicate single-block loops.
+ if (TailBB.isSuccessor(&TailBB))
+ return false;
+
+ // Set the limit on the cost to duplicate. When optimizing for size,
// duplicate only one, because one branch instruction can be eliminated to
// compensate for the duplication.
unsigned MaxDuplicateCount;
- if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
+ if (TailDuplicateSize.getNumOccurrences() == 0 &&
+ // FIXME: Use Function::optForSize().
+ MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize))
MaxDuplicateCount = 1;
else
MaxDuplicateCount = TailDuplicateSize;
- if (PreRegAlloc) {
- if (TailBB->empty())
- return false;
- const TargetInstrDesc &TID = TailBB->back().getDesc();
- // Pre-regalloc tail duplication hurts compile time and doesn't help
- // much except for indirect branches and returns.
- if (!TID.isIndirectBranch() && !TID.isReturn())
- return false;
- // If the target has hardware branch prediction that can handle indirect
- // branches, duplicating them can often make them predictable when there
- // are common paths through the code. The limit needs to be high enough
- // to allow undoing the effects of tail merging and other optimizations
- // that rearrange the predecessors of the indirect branch.
- MaxDuplicateCount = 20;
- }
+ // If the target has hardware branch prediction that can handle indirect
+ // branches, duplicating them can often make them predictable when there
+ // are common paths through the code. The limit needs to be high enough
+ // to allow undoing the effects of tail merging and other optimizations
+ // that rearrange the predecessors of the indirect branch.
- // Don't try to tail-duplicate single-block loops.
- if (TailBB->isSuccessor(TailBB))
- return false;
+ bool HasIndirectbr = false;
+ if (!TailBB.empty())
+ HasIndirectbr = TailBB.back().isIndirectBranch();
+
+ if (HasIndirectbr && PreRegAlloc)
+ MaxDuplicateCount = 20;
// Check the instructions in the block to determine whether tail-duplication
// is invalid or unlikely to be profitable.
unsigned InstrCount = 0;
- bool HasCall = false;
- for (MachineBasicBlock::iterator I = TailBB->begin();
- I != TailBB->end(); ++I) {
+ for (MachineInstr &MI : TailBB) {
// Non-duplicable things shouldn't be tail-duplicated.
- if (I->getDesc().isNotDuplicable()) return false;
+ if (MI.isNotDuplicable())
+ return false;
+
// Do not duplicate 'return' instructions if this is a pre-regalloc run.
// A return may expand into a lot more instructions (e.g. reload of callee
// saved registers) after PEI.
- if (PreRegAlloc && I->getDesc().isReturn()) return false;
- // Don't duplicate more than the threshold.
- if (InstrCount == MaxDuplicateCount) return false;
- // Remember if we saw a call.
- if (I->getDesc().isCall()) HasCall = true;
- if (!I->isPHI() && !I->isDebugValue())
+ if (PreRegAlloc && MI.isReturn())
+ return false;
+
+ // Avoid duplicating calls before register allocation. Calls presents a
+ // barrier to register allocation so duplicating them may end up increasing
+ // spills.
+ if (PreRegAlloc && MI.isCall())
+ return false;
+
+ if (!MI.isPHI() && !MI.isDebugValue())
InstrCount += 1;
+
+ if (InstrCount > MaxDuplicateCount)
+ return false;
}
- // Heuristically, don't tail-duplicate calls if it would expand code size,
- // as it's less likely to be worth the extra cost.
- if (InstrCount > 1 && (PreRegAlloc && HasCall))
+
+ // Check if any of the successors of TailBB has a PHI node in which the
+ // value corresponding to TailBB uses a subregister.
+ // If a phi node uses a register paired with a subregister, the actual
+ // "value type" of the phi may differ from the type of the register without
+ // any subregisters. Due to a bug, tail duplication may add a new operand
+ // without a necessary subregister, producing an invalid code. This is
+ // demonstrated by test/CodeGen/Hexagon/tail-dup-subreg-abort.ll.
+ // Disable tail duplication for this case for now, until the problem is
+ // fixed.
+ for (auto SB : TailBB.successors()) {
+ for (auto &I : *SB) {
+ if (!I.isPHI())
+ break;
+ unsigned Idx = getPHISrcRegOpIdx(&I, &TailBB);
+ assert(Idx != 0);
+ MachineOperand &PU = I.getOperand(Idx);
+ if (PU.getSubReg() != 0)
+ return false;
+ }
+ }
+
+ if (HasIndirectbr && PreRegAlloc)
+ return true;
+
+ if (IsSimple)
+ return true;
+
+ if (!PreRegAlloc)
+ return true;
+
+ return canCompletelyDuplicateBB(TailBB);
+}
+
+/// True if this BB has only one unconditional jump.
+bool
+TailDuplicatePass::isSimpleBB(MachineBasicBlock *TailBB) {
+ if (TailBB->succ_size() != 1)
+ return false;
+ if (TailBB->pred_empty())
return false;
+ MachineBasicBlock::iterator I = TailBB->getFirstNonDebugInstr();
+ if (I == TailBB->end())
+ return true;
+ return I->isUnconditionalBranch();
+}
+
+static bool
+bothUsedInPHI(const MachineBasicBlock &A,
+ SmallPtrSet<MachineBasicBlock*, 8> SuccsB) {
+ for (MachineBasicBlock *BB : A.successors())
+ if (SuccsB.count(BB) && !BB->empty() && BB->begin()->isPHI())
+ return true;
+
+ return false;
+}
+
+bool
+TailDuplicatePass::canCompletelyDuplicateBB(MachineBasicBlock &BB) {
+ for (MachineBasicBlock *PredBB : BB.predecessors()) {
+ if (PredBB->succ_size() > 1)
+ return false;
+
+ MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
+ SmallVector<MachineOperand, 4> PredCond;
+ if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
+ return false;
+
+ if (!PredCond.empty())
+ return false;
+ }
+ return true;
+}
+
+bool
+TailDuplicatePass::duplicateSimpleBB(MachineBasicBlock *TailBB,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+ const DenseSet<unsigned> &UsedByPhi,
+ SmallVectorImpl<MachineInstr *> &Copies) {
+ SmallPtrSet<MachineBasicBlock*, 8> Succs(TailBB->succ_begin(),
+ TailBB->succ_end());
+ SmallVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
+ TailBB->pred_end());
+ bool Changed = false;
+ for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
+ PE = Preds.end(); PI != PE; ++PI) {
+ MachineBasicBlock *PredBB = *PI;
+
+ if (PredBB->hasEHPadSuccessor())
+ continue;
+
+ if (bothUsedInPHI(*PredBB, Succs))
+ continue;
+
+ MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
+ SmallVector<MachineOperand, 4> PredCond;
+ if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
+ continue;
+ Changed = true;
+ DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
+ << "From simple Succ: " << *TailBB);
+
+ MachineBasicBlock *NewTarget = *TailBB->succ_begin();
+ MachineBasicBlock *NextBB = &*std::next(PredBB->getIterator());
+
+ // Make PredFBB explicit.
+ if (PredCond.empty())
+ PredFBB = PredTBB;
+
+ // Make fall through explicit.
+ if (!PredTBB)
+ PredTBB = NextBB;
+ if (!PredFBB)
+ PredFBB = NextBB;
+
+ // Redirect
+ if (PredFBB == TailBB)
+ PredFBB = NewTarget;
+ if (PredTBB == TailBB)
+ PredTBB = NewTarget;
+
+ // Make the branch unconditional if possible
+ if (PredTBB == PredFBB) {
+ PredCond.clear();
+ PredFBB = nullptr;
+ }
+
+ // Avoid adding fall through branches.
+ if (PredFBB == NextBB)
+ PredFBB = nullptr;
+ if (PredTBB == NextBB && PredFBB == nullptr)
+ PredTBB = nullptr;
+
+ TII->RemoveBranch(*PredBB);
+
+ if (PredTBB)
+ TII->InsertBranch(*PredBB, PredTBB, PredFBB, PredCond, DebugLoc());
+
+ auto Prob = MBPI->getEdgeProbability(PredBB, TailBB);
+ PredBB->removeSuccessor(TailBB);
+ unsigned NumSuccessors = PredBB->succ_size();
+ assert(NumSuccessors <= 1);
+ if (NumSuccessors == 0 || *PredBB->succ_begin() != NewTarget)
+ PredBB->addSuccessor(NewTarget, Prob);
+
+ TDBBs.push_back(PredBB);
+ }
+ return Changed;
+}
+
+/// If it is profitable, duplicate TailBB's contents in each
+/// of its predecessors.
+bool
+TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB,
+ bool IsSimple,
+ MachineFunction &MF,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+ SmallVectorImpl<MachineInstr *> &Copies) {
DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');
+ DenseSet<unsigned> UsedByPhi;
+ getRegsUsedByPHIs(*TailBB, &UsedByPhi);
+
+ if (IsSimple)
+ return duplicateSimpleBB(TailBB, TDBBs, UsedByPhi, Copies);
+
// Iterate through all the unique predecessors and tail-duplicate this
// block into them, if possible. Copying the list ahead of time also
// avoids trouble with the predecessor list reallocating.
assert(TailBB != PredBB &&
"Single-block loop should have been rejected earlier!");
- if (PredBB->succ_size() > 1) continue;
+ // EH edges are ignored by AnalyzeBranch.
+ if (PredBB->succ_size() > 1)
+ continue;
MachineBasicBlock *PredTBB, *PredFBB;
SmallVector<MachineOperand, 4> PredCond;
continue;
if (!PredCond.empty())
continue;
- // EH edges are ignored by AnalyzeBranch.
- if (PredBB->succ_size() != 1)
- continue;
// Don't duplicate into a fall-through predecessor (at least for now).
if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
continue;
// Remove PredBB's unconditional branch.
TII->RemoveBranch(*PredBB);
+ if (RS && !TailBB->livein_empty()) {
+ // Update PredBB livein.
+ RS->enterBasicBlock(PredBB);
+ if (!PredBB->empty())
+ RS->forward(std::prev(PredBB->end()));
+ for (const auto &LI : TailBB->liveins()) {
+ if (!RS->isRegUsed(LI.PhysReg, false))
+ // If a register is previously livein to the tail but it's not live
+ // at the end of predecessor BB, then it should be added to its
+ // livein list.
+ PredBB->addLiveIn(LI);
+ }
+ }
+
// Clone the contents of TailBB into PredBB.
DenseMap<unsigned, unsigned> LocalVRMap;
SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
- MachineBasicBlock::iterator I = TailBB->begin();
- while (I != TailBB->end()) {
+ // Use instr_iterator here to properly handle bundles, e.g.
+ // ARM Thumb2 IT block.
+ MachineBasicBlock::instr_iterator I = TailBB->instr_begin();
+ while (I != TailBB->instr_end()) {
MachineInstr *MI = &*I;
++I;
if (MI->isPHI()) {
// Replace the uses of the def of the PHI with the register coming
// from PredBB.
- ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos);
+ ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, true);
} else {
// Replace def of virtual registers with new registers, and update
// uses with PHI source register or the new registers.
- DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap);
+ DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap, UsedByPhi);
}
}
MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
TII->get(TargetOpcode::COPY),
CopyInfos[i].first).addReg(CopyInfos[i].second));
}
+
+ // Simplify
+ TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
+
NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
// Update the CFG.
"TailDuplicate called on block with multiple successors!");
for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
E = TailBB->succ_end(); I != E; ++I)
- PredBB->addSuccessor(*I);
+ PredBB->addSuccessor(*I, MBPI->getEdgeProbability(TailBB, I));
Changed = true;
++NumTailDups;
// If TailBB was duplicated into all its predecessors except for the prior
// block, which falls through unconditionally, move the contents of this
// block into the prior block.
- MachineBasicBlock *PrevBB = prior(MachineFunction::iterator(TailBB));
- MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
+ MachineBasicBlock *PrevBB = &*std::prev(TailBB->getIterator());
+ MachineBasicBlock *PriorTBB = nullptr, *PriorFBB = nullptr;
SmallVector<MachineOperand, 4> PriorCond;
- bool PriorUnAnalyzable =
- TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true);
// This has to check PrevBB->succ_size() because EH edges are ignored by
// AnalyzeBranch.
- if (!PriorUnAnalyzable && PriorCond.empty() && !PriorTBB &&
- TailBB->pred_size() == 1 && PrevBB->succ_size() == 1 &&
+ if (PrevBB->succ_size() == 1 &&
+ !TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true) &&
+ PriorCond.empty() && !PriorTBB && TailBB->pred_size() == 1 &&
!TailBB->hasAddressTaken()) {
DEBUG(dbgs() << "\nMerging into block: " << *PrevBB
<< "From MBB: " << *TailBB);
// Replace the uses of the def of the PHI with the register coming
// from PredBB.
MachineInstr *MI = &*I++;
- ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos);
+ ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos, UsedByPhi, true);
if (MI->getParent())
MI->eraseFromParent();
}
// Replace def of virtual registers with new registers, and update
// uses with PHI source register or the new registers.
MachineInstr *MI = &*I++;
- DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap);
+ assert(!MI->isBundle() && "Not expecting bundles before regalloc!");
+ DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap, UsedByPhi);
MI->eraseFromParent();
}
MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
Changed = true;
}
+ // If this is after register allocation, there are no phis to fix.
+ if (!PreRegAlloc)
+ return Changed;
+
+ // If we made no changes so far, we are safe.
+ if (!Changed)
+ return Changed;
+
+
+ // Handle the nasty case in that we duplicated a block that is part of a loop
+ // into some but not all of its predecessors. For example:
+ // 1 -> 2 <-> 3 |
+ // \ |
+ // \---> rest |
+ // if we duplicate 2 into 1 but not into 3, we end up with
+ // 12 -> 3 <-> 2 -> rest |
+ // \ / |
+ // \----->-----/ |
+ // If there was a "var = phi(1, 3)" in 2, it has to be ultimately replaced
+ // with a phi in 3 (which now dominates 2).
+ // What we do here is introduce a copy in 3 of the register defined by the
+ // phi, just like when we are duplicating 2 into 3, but we don't copy any
+ // real instructions or remove the 3 -> 2 edge from the phi in 2.
+ for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
+ PE = Preds.end(); PI != PE; ++PI) {
+ MachineBasicBlock *PredBB = *PI;
+ if (std::find(TDBBs.begin(), TDBBs.end(), PredBB) != TDBBs.end())
+ continue;
+
+ // EH edges
+ if (PredBB->succ_size() != 1)
+ continue;
+
+ DenseMap<unsigned, unsigned> LocalVRMap;
+ SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
+ MachineBasicBlock::iterator I = TailBB->begin();
+ // Process PHI instructions first.
+ while (I != TailBB->end() && I->isPHI()) {
+ // Replace the uses of the def of the PHI with the register coming
+ // from PredBB.
+ MachineInstr *MI = &*I++;
+ ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, false);
+ }
+ MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
+ for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
+ Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(),
+ TII->get(TargetOpcode::COPY),
+ CopyInfos[i].first).addReg(CopyInfos[i].second));
+ }
+ }
+
return Changed;
}
-/// RemoveDeadBlock - Remove the specified dead machine basic block from the
-/// function, updating the CFG.
+/// Remove the specified dead machine basic block from the function, updating
+/// the CFG.
void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
assert(MBB->pred_empty() && "MBB must be dead!");
DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
// Remove the block.
MBB->eraseFromParent();
}
-
projects / oota-llvm.git / blobdiff