//===----------------------------------------------------------------------===//
#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/OwningPtr.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/Target/TargetInstrInfo.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/MachineSSAUpdater.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"
using namespace llvm;
+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>
cl::desc("Maximum instructions to consider tail duplicating"),
cl::init(2), cl::Hidden);
+static cl::opt<bool>
+TailDupVerify("tail-dup-verify",
+ cl::desc("Verify sanity of PHI instructions during taildup"),
+ cl::init(false), cl::Hidden);
+
+static cl::opt<unsigned>
+TailDupLimit("tail-dup-limit", cl::init(~0U), cl::Hidden);
+
+typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy;
+
namespace {
/// TailDuplicatePass - Perform tail duplication.
class TailDuplicatePass : public MachineFunctionPass {
const TargetInstrInfo *TII;
+ const TargetRegisterInfo *TRI;
+ const MachineBranchProbabilityInfo *MBPI;
MachineModuleInfo *MMI;
+ MachineRegisterInfo *MRI;
+ OwningPtr<RegScavenger> RS;
+ bool PreRegAlloc;
+
+ // SSAUpdateVRs - 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.
+ DenseMap<unsigned, AvailableValsTy> SSAUpdateVals;
public:
static char ID;
- explicit TailDuplicatePass() : MachineFunctionPass(&ID) {}
+ explicit TailDuplicatePass() :
+ MachineFunctionPass(ID), PreRegAlloc(false) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
- virtual const char *getPassName() const { return "Tail Duplication"; }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const;
private:
+ void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg,
+ MachineBasicBlock *BB);
+ void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB,
+ MachineBasicBlock *PredBB,
+ DenseMap<unsigned, unsigned> &LocalVRMap,
+ 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,
+ const DenseSet<unsigned> &UsedByPhi);
+ void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+ SmallSetVector<MachineBasicBlock*, 8> &Succs);
bool TailDuplicateBlocks(MachineFunction &MF);
- bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF);
+ 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() {
- return new TailDuplicatePass();
-}
+char &llvm::TailDuplicateID = TailDuplicatePass::ID;
+
+INITIALIZE_PASS(TailDuplicatePass, "tailduplication", "Tail Duplication",
+ false, false)
bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
TII = MF.getTarget().getInstrInfo();
+ TRI = MF.getTarget().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;
- bool MadeChangeThisIteration = true;
- while (MadeChangeThisIteration) {
- MadeChangeThisIteration = false;
- MadeChangeThisIteration |= TailDuplicateBlocks(MF);
- MadeChange |= MadeChangeThisIteration;
- }
+ while (TailDuplicateBlocks(MF))
+ MadeChange = true;
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;
+ SmallSetVector<MachineBasicBlock*, 8> Preds(MBB->pred_begin(),
+ MBB->pred_end());
+ MachineBasicBlock::iterator MI = MBB->begin();
+ while (MI != MBB->end()) {
+ if (!MI->isPHI())
+ break;
+ for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
+ PE = Preds.end(); PI != PE; ++PI) {
+ MachineBasicBlock *PredBB = *PI;
+ bool Found = false;
+ for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
+ MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
+ if (PHIBB == PredBB) {
+ Found = true;
+ break;
+ }
+ }
+ if (!Found) {
+ dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
+ dbgs() << " missing input from predecessor BB#"
+ << PredBB->getNumber() << '\n';
+ llvm_unreachable(0);
+ }
+ }
+
+ for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
+ MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB();
+ if (CheckExtra && !Preds.count(PHIBB)) {
+ dbgs() << "Warning: malformed PHI in BB#" << MBB->getNumber()
+ << ": " << *MI;
+ dbgs() << " extra input from predecessor BB#"
+ << PHIBB->getNumber() << '\n';
+ llvm_unreachable(0);
+ }
+ if (PHIBB->getNumber() < 0) {
+ dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI;
+ dbgs() << " non-existing BB#" << PHIBB->getNumber() << '\n';
+ llvm_unreachable(0);
+ }
+ }
+ ++MI;
+ }
+ }
+}
+
+/// TailDuplicateAndUpdate - 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;
+
+ ++NumTails;
+
+ SmallVector<MachineInstr*, 8> NewPHIs;
+ MachineSSAUpdater SSAUpdate(MF, &NewPHIs);
+
+ // 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;
+ }
+
+ // 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);
+ }
+
+ // 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);
+ }
+
+ // 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->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);
+ }
+ }
+
+ SSAUpdateVRs.clear();
+ SSAUpdateVals.clear();
+ }
+
+ // 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 (NewPHIs.size())
+ NumAddedPHIs += NewPHIs.size();
+
+ return true;
+}
+
/// 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;
+ if (PreRegAlloc && TailDupVerify) {
+ DEBUG(dbgs() << "\n*** Before tail-duplicating\n");
+ VerifyPHIs(MF, true);
+ }
+
for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
MachineBasicBlock *MBB = I++;
- // Only duplicate blocks that end with unconditional branches.
- if (MBB->canFallThrough())
+ if (NumTails == TailDupLimit)
+ break;
+
+ bool IsSimple = isSimpleBB(MBB);
+
+ if (!shouldTailDuplicate(MF, IsSimple, *MBB))
continue;
- MadeChange |= TailDuplicate(MBB, MF);
+ MadeChange |= TailDuplicateAndUpdate(MBB, IsSimple, MF);
+ }
+
+ if (PreRegAlloc && TailDupVerify)
+ VerifyPHIs(MF, false);
- // If it is dead, remove it.
- if (MBB->pred_empty()) {
- NumInstrDups -= MBB->size();
- RemoveDeadBlock(MBB);
- MadeChange = true;
- ++NumDeadBlocks;
+ 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->isDebugValue())
+ continue;
+ if (UseMI->getParent() != BB)
+ return true;
+ }
+ return false;
+}
+
+static unsigned getPHISrcRegOpIdx(MachineInstr *MI, MachineBasicBlock *SrcBB) {
+ for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2)
+ if (MI->getOperand(i+1).getMBB() == SrcBB)
+ return i;
+ return 0;
+}
+
+
+// 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(MachineBasicBlock::const_iterator I = BB.begin(), E = BB.end();
+ I != E; ++I) {
+ const MachineInstr &MI = *I;
+ if (!MI.isPHI())
+ break;
+ for (unsigned i = 1, e = MI.getNumOperands(); i != e; i += 2) {
+ unsigned SrcReg = MI.getOperand(i).getReg();
+ UsedByPhi->insert(SrcReg);
}
}
- return MadeChange;
}
-/// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
-/// of its predecessors.
-bool TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB,
- MachineFunction &MF) {
+/// AddSSAUpdateEntry - 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);
+ if (LI != SSAUpdateVals.end())
+ LI->second.push_back(std::make_pair(BB, NewReg));
+ else {
+ AvailableValsTy Vals;
+ Vals.push_back(std::make_pair(BB, NewReg));
+ SSAUpdateVals.insert(std::make_pair(OrigReg, Vals));
+ SSAUpdateVRs.push_back(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,
+ 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?");
+ unsigned SrcReg = MI->getOperand(SrcOpIdx).getReg();
+ const TargetRegisterClass *RC = MRI->getRegClass(DefReg);
+ LocalVRMap.insert(std::make_pair(DefReg, SrcReg));
+
+ // Insert a copy from source to the end of the block. The def register is the
+ // available value liveout of the block.
+ unsigned NewDef = MRI->createVirtualRegister(RC);
+ Copies.push_back(std::make_pair(NewDef, SrcReg));
+ 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);
+ if (MI->getNumOperands() == 1)
+ MI->eraseFromParent();
+}
+
+/// DuplicateInstruction - 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,
+ 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);
+ if (!MO.isReg())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!TargetRegisterInfo::isVirtualRegister(Reg))
+ continue;
+ if (MO.isDef()) {
+ const TargetRegisterClass *RC = MRI->getRegClass(Reg);
+ unsigned NewReg = MRI->createVirtualRegister(RC);
+ MO.setReg(NewReg);
+ LocalVRMap.insert(std::make_pair(Reg, NewReg));
+ 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()) {
+ MO.setReg(VI->second);
+ MRI->constrainRegClass(VI->second, MRI->getRegClass(Reg));
+ }
+ }
+ }
+ 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.
+void
+TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
+ SmallVectorImpl<MachineBasicBlock *> &TDBBs,
+ SmallSetVector<MachineBasicBlock*,8> &Succs) {
+ for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(),
+ SE = Succs.end(); SI != SE; ++SI) {
+ MachineBasicBlock *SuccBB = *SI;
+ for (MachineBasicBlock::iterator II = SuccBB->begin(), EE = SuccBB->end();
+ 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);
+ if (MO.getMBB() == FromBB) {
+ Idx = i;
+ break;
+ }
+ }
+
+ assert(Idx != 0);
+ MachineOperand &MO0 = II->getOperand(Idx);
+ unsigned Reg = MO0.getReg();
+ if (isDead) {
+ // Folded into the previous BB.
+ // There could be duplicate phi source entries. FIXME: Should sdisel
+ // or earlier pass fixed this?
+ for (unsigned i = II->getNumOperands()-2; i != Idx; i -= 2) {
+ MachineOperand &MO = II->getOperand(i+1);
+ if (MO.getMBB() == FromBB) {
+ II->RemoveOperand(i+1);
+ II->RemoveOperand(i);
+ }
+ }
+ } else
+ Idx = 0;
+
+ // If Idx is set, the operands at Idx and Idx+1 must be removed.
+ // We reuse the location to avoid expensive RemoveOperand calls.
+
+ DenseMap<unsigned,AvailableValsTy>::iterator LI=SSAUpdateVals.find(Reg);
+ if (LI != SSAUpdateVals.end()) {
+ // 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 {
+ MIB.addReg(SrcReg).addMBB(SrcBB);
+ }
+ }
+ } else {
+ // Live in tail block, must also be live in predecessors.
+ for (unsigned j = 0, ee = TDBBs.size(); j != ee; ++j) {
+ MachineBasicBlock *SrcBB = TDBBs[j];
+ if (Idx != 0) {
+ II->getOperand(Idx).setReg(Reg);
+ II->getOperand(Idx+1).setMBB(SrcBB);
+ Idx = 0;
+ } else {
+ MIB.addReg(Reg).addMBB(SrcBB);
+ }
+ }
+ }
+ if (Idx != 0) {
+ II->RemoveOperand(Idx+1);
+ II->RemoveOperand(Idx);
+ }
+ }
+ }
+}
+
+/// shouldTailDuplicate - Determine if it is profitable to duplicate this block.
+bool
+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))
+ if (TailBB.isSuccessor(&TailBB))
return false;
- // 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,
+ // 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 (!TailBB->empty() && TailBB->back().getDesc().isIndirectBranch())
- // 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.
- MaxDuplicateCount = 20;
- else if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
+ if (TailDuplicateSize.getNumOccurrences() == 0 &&
+ MF.getFunction()->getAttributes().
+ hasAttribute(AttributeSet::FunctionIndex, Attribute::OptimizeForSize))
MaxDuplicateCount = 1;
else
MaxDuplicateCount = TailDuplicateSize;
+ // 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.
+
+ 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 i = 0;
- bool HasCall = false;
- for (MachineBasicBlock::iterator I = TailBB->begin();
- I != TailBB->end(); ++I, ++i) {
+ unsigned InstrCount = 0;
+ for (MachineBasicBlock::iterator I = TailBB.begin(); I != TailBB.end(); ++I) {
// Non-duplicable things shouldn't be tail-duplicated.
- if (I->getDesc().isNotDuplicable()) return false;
- // Don't duplicate more than the threshold.
- if (i == MaxDuplicateCount) return false;
- // Remember if we saw a call.
- if (I->getDesc().isCall()) HasCall = true;
- }
- // Heuristically, don't tail-duplicate calls if it would expand code size,
- // as it's less likely to be worth the extra cost.
- if (i > 1 && HasCall)
+ if (I->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->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 && I->isCall())
+ return false;
+
+ if (!I->isPHI() && !I->isDebugValue())
+ InstrCount += 1;
+
+ if (InstrCount > MaxDuplicateCount)
+ return false;
+ }
+
+ if (HasIndirectbr && PreRegAlloc)
+ return true;
+
+ if (IsSimple)
+ return true;
+
+ if (!PreRegAlloc)
+ return true;
+
+ return canCompletelyDuplicateBB(TailBB);
+}
+
+/// isSimpleBB - 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->begin();
+ MachineBasicBlock::iterator E = TailBB->end();
+ while (I != E && I->isDebugValue())
+ ++I;
+ if (I == E)
+ return true;
+ return I->isUnconditionalBranch();
+}
+
+static bool
+bothUsedInPHI(const MachineBasicBlock &A,
+ SmallPtrSet<MachineBasicBlock*, 8> SuccsB) {
+ for (MachineBasicBlock::const_succ_iterator SI = A.succ_begin(),
+ SE = A.succ_end(); SI != SE; ++SI) {
+ MachineBasicBlock *BB = *SI;
+ if (SuccsB.count(BB) && !BB->empty() && BB->begin()->isPHI())
+ return true;
+ }
+
+ return false;
+}
+
+bool
+TailDuplicatePass::canCompletelyDuplicateBB(MachineBasicBlock &BB) {
+ for (MachineBasicBlock::pred_iterator PI = BB.pred_begin(),
+ PE = BB.pred_end(); PI != PE; ++PI) {
+ MachineBasicBlock *PredBB = *PI;
+
+ if (PredBB->succ_size() > 1)
+ return false;
+
+ MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
+ 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->getLandingPadSuccessor())
+ continue;
+
+ if (bothUsedInPHI(*PredBB, Succs))
+ continue;
+
+ MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
+ 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 = llvm::next(MachineFunction::iterator(PredBB));
+
+ // 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 = NULL;
+ }
+
+ // Avoid adding fall through branches.
+ if (PredFBB == NextBB)
+ PredFBB = NULL;
+ if (PredTBB == NextBB && PredFBB == NULL)
+ PredTBB = NULL;
+
+ TII->RemoveBranch(*PredBB);
+
+ if (PredTBB)
+ TII->InsertBranch(*PredBB, PredTBB, PredFBB, PredCond, DebugLoc());
+
+ uint32_t Weight = MBPI->getEdgeWeight(PredBB, TailBB);
+ PredBB->removeSuccessor(TailBB);
+ unsigned NumSuccessors = PredBB->succ_size();
+ assert(NumSuccessors <= 1);
+ if (NumSuccessors == 0 || *PredBB->succ_begin() != NewTarget)
+ PredBB->addSuccessor(NewTarget, Weight);
+
+ TDBBs.push_back(PredBB);
+ }
+ return Changed;
+}
+
+/// TailDuplicate - 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.
bool Changed = false;
- SmallSetVector<MachineBasicBlock *, 8> Preds(TailBB->pred_begin(),
- TailBB->pred_end());
+ SmallSetVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(),
+ TailBB->pred_end());
for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(),
PE = Preds.end(); PI != PE; ++PI) {
MachineBasicBlock *PredBB = *PI;
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;
- DEBUG(errs() << "\nTail-duplicating into PredBB: " << *PredBB
+ DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB
<< "From Succ: " << *TailBB);
+ TDBBs.push_back(PredBB);
+
// Remove PredBB's unconditional branch.
TII->RemoveBranch(*PredBB);
+
+ if (RS && !TailBB->livein_empty()) {
+ // Update PredBB livein.
+ RS->enterBasicBlock(PredBB);
+ if (!PredBB->empty())
+ RS->forward(prior(PredBB->end()));
+ BitVector RegsLiveAtExit(TRI->getNumRegs());
+ RS->getRegsUsed(RegsLiveAtExit, false);
+ for (MachineBasicBlock::livein_iterator I = TailBB->livein_begin(),
+ E = TailBB->livein_end(); I != E; ++I) {
+ if (!RegsLiveAtExit[*I])
+ // 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(*I);
+ }
+ }
+
// Clone the contents of TailBB into PredBB.
- for (MachineBasicBlock::iterator I = TailBB->begin(), E = TailBB->end();
- I != E; ++I) {
- MachineInstr *NewMI = MF.CloneMachineInstr(I);
- PredBB->insert(PredBB->end(), NewMI);
+ DenseMap<unsigned, unsigned> LocalVRMap;
+ SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
+ // 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, 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, UsedByPhi);
+ }
+ }
+ 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));
}
+
+ // Simplify
+ TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
+
NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
// Update the CFG.
assert(PredBB->succ_empty() &&
"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);
+ E = TailBB->succ_end(); I != E; ++I)
+ PredBB->addSuccessor(*I, MBPI->getEdgeWeight(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 *PrevBB = prior(MachineFunction::iterator(TailBB));
MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
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(errs() << "\nMerging into block: " << PrevBB
+ DEBUG(dbgs() << "\nMerging into block: " << *PrevBB
<< "From MBB: " << *TailBB);
- PrevBB.splice(PrevBB.end(), TailBB, TailBB->begin(), TailBB->end());
- PrevBB.removeSuccessor(PrevBB.succ_begin());;
- assert(PrevBB.succ_empty());
- PrevBB.transferSuccessors(TailBB);
+ if (PreRegAlloc) {
+ 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, PrevBB, LocalVRMap, CopyInfos, UsedByPhi, true);
+ if (MI->getParent())
+ MI->eraseFromParent();
+ }
+
+ // Now copy the non-PHI instructions.
+ while (I != TailBB->end()) {
+ // Replace def of virtual registers with new registers, and update
+ // uses with PHI source register or the new registers.
+ MachineInstr *MI = &*I++;
+ assert(!MI->isBundle() && "Not expecting bundles before regalloc!");
+ DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap, UsedByPhi);
+ MI->eraseFromParent();
+ }
+ MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
+ for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
+ Copies.push_back(BuildMI(*PrevBB, Loc, DebugLoc(),
+ TII->get(TargetOpcode::COPY),
+ CopyInfos[i].first)
+ .addReg(CopyInfos[i].second));
+ }
+ } else {
+ // No PHIs to worry about, just splice the instructions over.
+ PrevBB->splice(PrevBB->end(), TailBB, TailBB->begin(), TailBB->end());
+ }
+ PrevBB->removeSuccessor(PrevBB->succ_begin());
+ assert(PrevBB->succ_empty());
+ PrevBB->transferSuccessors(TailBB);
+ TDBBs.push_back(PrevBB);
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;
}
/// function, updating the CFG.
void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) {
assert(MBB->pred_empty() && "MBB must be dead!");
- DEBUG(errs() << "\nRemoving MBB: " << *MBB);
+ DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
// Remove all successors.
while (!MBB->succ_empty())
MBB->removeSuccessor(MBB->succ_end()-1);
- // If there are any labels in the basic block, unregister them from
- // MachineModuleInfo.
- if (MMI && !MBB->empty()) {
- for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
- I != E; ++I) {
- if (I->isLabel())
- // The label ID # is always operand #0, an immediate.
- MMI->InvalidateLabel(I->getOperand(0).getImm());
- }
- }
-
// Remove the block.
MBB->eraseFromParent();
}
-
projects / oota-llvm.git / blobdiff