STATISTIC(NumTailMerge , "Number of block tails merged");
static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
cl::init(cl::BOU_UNSET), cl::Hidden);
-namespace {
- // Throttle for huge numbers of predecessors (compile speed problems)
- static cl::opt<unsigned>
- TailMergeThreshold("tail-merge-threshold",
- cl::desc("Max number of predecessors to consider tail merging"),
- cl::init(100), cl::Hidden);
+// Throttle for huge numbers of predecessors (compile speed problems)
+static cl::opt<unsigned>
+TailMergeThreshold("tail-merge-threshold",
+ cl::desc("Max number of predecessors to consider tail merging"),
+ cl::init(150), cl::Hidden);
+namespace {
struct VISIBILITY_HIDDEN BranchFolder : public MachineFunctionPass {
static char ID;
explicit BranchFolder(bool defaultEnableTailMerge) :
- MachineFunctionPass((intptr_t)&ID) {
- switch (FlagEnableTailMerge) {
- case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;
- case cl::BOU_TRUE: EnableTailMerge = true; break;
- case cl::BOU_FALSE: EnableTailMerge = false; break;
- }
+ MachineFunctionPass(&ID) {
+ switch (FlagEnableTailMerge) {
+ case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;
+ case cl::BOU_TRUE: EnableTailMerge = true; break;
+ case cl::BOU_FALSE: EnableTailMerge = false; break;
+ }
}
virtual bool runOnMachineFunction(MachineFunction &MF);
unsigned ComputeSameTails(unsigned CurHash, unsigned minCommonTailLength);
void RemoveBlocksWithHash(unsigned CurHash, MachineBasicBlock* SuccBB,
MachineBasicBlock* PredBB);
+ unsigned CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
+ unsigned maxCommonTailLength);
typedef std::pair<unsigned,MachineBasicBlock*> MergePotentialsElt;
typedef std::vector<MergePotentialsElt>::iterator MPIterator;
std::vector<MergePotentialsElt> MergePotentials;
+
typedef std::pair<MPIterator, MachineBasicBlock::iterator> SameTailElt;
std::vector<SameTailElt> SameTails;
bool CanFallThrough(MachineBasicBlock *CurBB);
bool CanFallThrough(MachineBasicBlock *CurBB, bool BranchUnAnalyzable,
MachineBasicBlock *TBB, MachineBasicBlock *FBB,
- const std::vector<MachineOperand> &Cond);
+ const SmallVectorImpl<MachineOperand> &Cond);
};
char BranchFolder::ID = 0;
}
while (!MBB->succ_empty())
MBB->removeSuccessor(MBB->succ_end()-1);
- // If there is DWARF info to active, check to see if there are any LABEL
- // records in the basic block. If so, unregister them from MachineModuleInfo.
+ // 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 ((unsigned)I->getOpcode() == TargetInstrInfo::LABEL) {
+ if (I->isLabel())
// The label ID # is always operand #0, an immediate.
MMI->InvalidateLabel(I->getOperand(0).getImm());
- }
}
}
// Remove the block.
- MF->getBasicBlockList().erase(MBB);
+ MF->erase(MBB);
}
/// OptimizeImpDefsBlock - If a basic block is just a bunch of implicit_def
bool EverMadeChange = false;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; I++) {
MachineBasicBlock *MBB = I, *TBB = 0, *FBB = 0;
- std::vector<MachineOperand> Cond;
+ SmallVector<MachineOperand, 4> Cond;
if (!TII->AnalyzeBranch(*MBB, TBB, FBB, Cond))
EverMadeChange |= MBB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
EverMadeChange |= OptimizeImpDefsBlock(MBB);
I != E; ++I)
for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) {
MachineOperand &Op = I->getOperand(op);
- if (!Op.isJumpTableIndex()) continue;
+ if (!Op.isJTI()) continue;
unsigned NewIdx = JTMapping[Op.getIndex()];
Op.setIndex(NewIdx);
// If OldBB isn't immediately before OldBB, insert a branch to it.
if (++MachineFunction::iterator(OldBB) != MachineFunction::iterator(NewDest))
- TII->InsertBranch(*OldBB, NewDest, 0, std::vector<MachineOperand>());
+ TII->InsertBranch(*OldBB, NewDest, 0, SmallVector<MachineOperand, 0>());
OldBB->addSuccessor(NewDest);
++NumTailMerge;
}
/// iterator. This returns the new MBB.
MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
MachineBasicBlock::iterator BBI1) {
+ MachineFunction &MF = *CurMBB.getParent();
+
// Create the fall-through block.
MachineFunction::iterator MBBI = &CurMBB;
- MachineBasicBlock *NewMBB = new MachineBasicBlock(CurMBB.getBasicBlock());
- CurMBB.getParent()->getBasicBlockList().insert(++MBBI, NewMBB);
+ MachineBasicBlock *NewMBB =MF.CreateMachineBasicBlock(CurMBB.getBasicBlock());
+ CurMBB.getParent()->insert(++MBBI, NewMBB);
// Move all the successors of this block to the specified block.
- while (!CurMBB.succ_empty()) {
- MachineBasicBlock *S = *(CurMBB.succ_end()-1);
- NewMBB->addSuccessor(S);
- CurMBB.removeSuccessor(S);
- }
+ NewMBB->transferSuccessors(&CurMBB);
// Add an edge from CurMBB to NewMBB for the fall-through.
CurMBB.addSuccessor(NewMBB);
return Time;
}
-/// ShouldSplitFirstBlock - We need to either split MBB1 at MBB1I or MBB2 at
-/// MBB2I and then insert an unconditional branch in the other block. Determine
-/// which is the best to split
-static bool ShouldSplitFirstBlock(MachineBasicBlock *MBB1,
- MachineBasicBlock::iterator MBB1I,
- MachineBasicBlock *MBB2,
- MachineBasicBlock::iterator MBB2I,
- MachineBasicBlock *PredBB) {
- // If one block is the entry block, split the other one; we can't generate
- // a branch to the entry block, as its label is not emitted.
- MachineBasicBlock *Entry = MBB1->getParent()->begin();
- if (MBB1 == Entry)
- return false;
- if (MBB2 == Entry)
- return true;
-
- // If one block falls through into the common successor, choose that
- // one to split; it is one instruction less to do that.
- if (PredBB) {
- if (MBB1 == PredBB)
- return true;
- else if (MBB2 == PredBB)
- return false;
- }
- // TODO: if we had some notion of which block was hotter, we could split
- // the hot block, so it is the fall-through. Since we don't have profile info
- // make a decision based on which will hurt most to split.
- unsigned MBB1Time = EstimateRuntime(MBB1->begin(), MBB1I);
- unsigned MBB2Time = EstimateRuntime(MBB2->begin(), MBB2I);
-
- // If the MBB1 prefix takes "less time" to run than the MBB2 prefix, split the
- // MBB1 block so it falls through. This will penalize the MBB2 path, but will
- // have a lower overall impact on the program execution.
- return MBB1Time < MBB2Time;
-}
-
// CurMBB needs to add an unconditional branch to SuccMBB (we removed these
// branches temporarily for tail merging). In the case where CurMBB ends
// with a conditional branch to the next block, optimize by reversing the
MachineFunction *MF = CurMBB->getParent();
MachineFunction::iterator I = next(MachineFunction::iterator(CurMBB));
MachineBasicBlock *TBB = 0, *FBB = 0;
- std::vector<MachineOperand> Cond;
+ SmallVector<MachineOperand, 4> Cond;
if (I != MF->end() &&
!TII->AnalyzeBranch(*CurMBB, TBB, FBB, Cond)) {
MachineBasicBlock *NextBB = I;
}
}
}
- TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector<MachineOperand>());
+ TII->InsertBranch(*CurMBB, SuccBB, NULL, SmallVector<MachineOperand, 0>());
}
static bool MergeCompare(const std::pair<unsigned,MachineBasicBlock*> &p,
CurMPIter->second,
I->second,
TrialBBI1, TrialBBI2);
- if (CommonTailLen >= minCommonTailLength) {
+ // If we will have to split a block, there should be at least
+ // minCommonTailLength instructions in common; if not, at worst
+ // we will be replacing a fallthrough into the common tail with a
+ // branch, which at worst breaks even with falling through into
+ // the duplicated common tail, so 1 instruction in common is enough.
+ // We will always pick a block we do not have to split as the common
+ // tail if there is one.
+ // (Empty blocks will get forwarded and need not be considered.)
+ if (CommonTailLen >= minCommonTailLength ||
+ (CommonTailLen > 0 &&
+ (TrialBBI1==CurMPIter->second->begin() ||
+ TrialBBI2==I->second->begin()))) {
if (CommonTailLen > maxCommonTailLength) {
SameTails.clear();
maxCommonTailLength = CommonTailLen;
void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
MachineBasicBlock* SuccBB,
MachineBasicBlock* PredBB) {
- for (MPIterator CurMPIter = prior(MergePotentials.end()),
- B = MergePotentials.begin();
+ MPIterator CurMPIter, B;
+ for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin();
CurMPIter->first==CurHash;
--CurMPIter) {
// Put the unconditional branch back, if we need one.
MachineBasicBlock *CurMBB = CurMPIter->second;
if (SuccBB && CurMBB != PredBB)
FixTail(CurMBB, SuccBB, TII);
- MergePotentials.erase(CurMPIter);
- if (CurMPIter==B)
+ if (CurMPIter==B)
+ break;
+ }
+ if (CurMPIter->first!=CurHash)
+ CurMPIter++;
+ MergePotentials.erase(CurMPIter, MergePotentials.end());
+}
+
+/// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist
+/// only of the common tail. Create a block that does by splitting one.
+unsigned BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
+ unsigned maxCommonTailLength) {
+ unsigned i, commonTailIndex;
+ unsigned TimeEstimate = ~0U;
+ for (i=0, commonTailIndex=0; i<SameTails.size(); i++) {
+ // Use PredBB if possible; that doesn't require a new branch.
+ if (SameTails[i].first->second==PredBB) {
+ commonTailIndex = i;
break;
+ }
+ // Otherwise, make a (fairly bogus) choice based on estimate of
+ // how long it will take the various blocks to execute.
+ unsigned t = EstimateRuntime(SameTails[i].first->second->begin(),
+ SameTails[i].second);
+ if (t<=TimeEstimate) {
+ TimeEstimate = t;
+ commonTailIndex = i;
+ }
}
+
+ MachineBasicBlock::iterator BBI = SameTails[commonTailIndex].second;
+ MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second;
+
+ DOUT << "\nSplitting " << MBB->getNumber() << ", size " <<
+ maxCommonTailLength;
+
+ MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI);
+ SameTails[commonTailIndex].first->second = newMBB;
+ SameTails[commonTailIndex].second = newMBB->begin();
+ // If we split PredBB, newMBB is the new predecessor.
+ if (PredBB==MBB)
+ PredBB = newMBB;
+
+ return commonTailIndex;
}
// See if any of the blocks in MergePotentials (which all have a common single
bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
MachineBasicBlock* PredBB) {
- // We cannot jump to the entry block, which affects various choices below.
- MachineBasicBlock *Entry = MergePotentials.begin()->second->
- getParent()->begin();
-
// It doesn't make sense to save a single instruction since tail merging
// will add a jump.
// FIXME: Ask the target to provide the threshold?
}
// If one of the blocks is the entire common tail (and not the entry
- // block, which we can't jump to), treat all blocks with this same
- // tail at once.
- unsigned int i;
- for (i=0; i<SameTails.size(); i++) {
+ // block, which we can't jump to), we can treat all blocks with this same
+ // tail at once. Use PredBB if that is one of the possibilities, as that
+ // will not introduce any extra branches.
+ MachineBasicBlock *EntryBB = MergePotentials.begin()->second->
+ getParent()->begin();
+ unsigned int commonTailIndex, i;
+ for (commonTailIndex=SameTails.size(), i=0; i<SameTails.size(); i++) {
MachineBasicBlock *MBB = SameTails[i].first->second;
- if (MBB->begin() == SameTails[i].second && MBB != Entry)
- break;
- }
- if (i!=SameTails.size()) {
- MachineBasicBlock *MBB = SameTails[i].first->second;
- // MBB is common tail. Adjust all other BB's to jump to this one.
- // Traversal must be forwards so erases work.
- DOUT << "\nUsing common tail " << MBB->getNumber() << " for ";
- for (unsigned int j=0; j<SameTails.size(); ++j) {
- if (i==j)
- continue;
- DOUT << SameTails[j].first->second->getNumber() << ",";
- // Hack the end off BB j, making it jump to BB i instead.
- ReplaceTailWithBranchTo(SameTails[j].second, MBB);
- // This modifies BB j, so remove it from the worklist.
- MergePotentials.erase(SameTails[j].first);
+ if (MBB->begin() == SameTails[i].second && MBB != EntryBB) {
+ commonTailIndex = i;
+ if (MBB==PredBB)
+ break;
}
- DOUT << "\n";
- // We leave i in the worklist in case there are other blocks that
- // match it with a smaller number of instructions.
- MadeChange = true;
- continue;
}
- // Otherwise, merge the 2 blocks in SameTails that are latest in
- // MergePotentials; these are at indices 0 and 1 in SameTails.
- MachineBasicBlock::iterator BBI1 = (SameTails[0]).second;
- MachineBasicBlock::iterator BBI2 = (SameTails[1]).second;
- MachineBasicBlock *MBB1 = (SameTails[0]).first->second;
- MachineBasicBlock *MBB2 = (SameTails[1]).first->second;
-
- DOUT << "\nMerging " << MBB1->getNumber() << "," <<
- MBB2->getNumber() << ", size " << maxCommonTailLength;
-
- // Neither block is the entire common tail; split the tail of one block
- // to make it redundant with the other tail. We cannot jump to the
- // entry block, so if one block is the entry block, split the other one.
-
- // The second half of the split block will remain in SameTails, and will
- // consist entirely of common code. Thus in the case where there are
- // multiple blocks that would all need to be split, the next iteration of
- // the outer loop will handle all the rest of them.
-
- // Decide whether we want to split MBB1 or MBB2.
- if (ShouldSplitFirstBlock(MBB1, BBI1, MBB2, BBI2, PredBB)) {
- MBB1 = SplitMBBAt(*MBB1, BBI1);
- BBI1 = MBB1->begin();
- SameTails[0].first->second = MBB1;
- } else {
- MBB2 = SplitMBBAt(*MBB2, BBI2);
- BBI2 = MBB2->begin();
- SameTails[1].first->second = MBB2;
+ if (commonTailIndex==SameTails.size()) {
+ // None of the blocks consist entirely of the common tail.
+ // Split a block so that one does.
+ commonTailIndex = CreateCommonTailOnlyBlock(PredBB, maxCommonTailLength);
}
-
- if (MBB2->begin() == BBI2 && MBB2 != Entry) {
- // Hack the end off MBB1, making it jump to MBB2 instead.
- ReplaceTailWithBranchTo(BBI1, MBB2);
- // This modifies MBB1, so remove it from the worklist.
- MergePotentials.erase(SameTails[0].first);
- } else {
- assert(MBB1->begin() == BBI1 && MBB1 != Entry &&
- "Didn't split block correctly?");
- // Hack the end off MBB2, making it jump to MBB1 instead.
- ReplaceTailWithBranchTo(BBI2, MBB1);
- // This modifies MBB2, so remove it from the worklist.
- MergePotentials.erase(SameTails[1].first);
+
+ MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second;
+ // MBB is common tail. Adjust all other BB's to jump to this one.
+ // Traversal must be forwards so erases work.
+ DOUT << "\nUsing common tail " << MBB->getNumber() << " for ";
+ for (unsigned int i=0; i<SameTails.size(); ++i) {
+ if (commonTailIndex==i)
+ continue;
+ DOUT << SameTails[i].first->second->getNumber() << ",";
+ // Hack the end off BB i, making it jump to BB commonTailIndex instead.
+ ReplaceTailWithBranchTo(SameTails[i].second, MBB);
+ // BB i is no longer a predecessor of SuccBB; remove it from the worklist.
+ MergePotentials.erase(SameTails[i].first);
}
+ DOUT << "\n";
+ // We leave commonTailIndex in the worklist in case there are other blocks
+ // that match it with a smaller number of instructions.
MadeChange = true;
}
return MadeChange;
// transformations.)
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
- if (!I->succ_empty() && I->pred_size() >= 2 &&
- I->pred_size() < TailMergeThreshold) {
+ if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) {
MachineBasicBlock *IBB = I;
MachineBasicBlock *PredBB = prior(I);
MergePotentials.clear();
if (PBB==IBB)
continue;
MachineBasicBlock *TBB = 0, *FBB = 0;
- std::vector<MachineOperand> Cond;
+ SmallVector<MachineOperand, 4> Cond;
if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond)) {
// Failing case: IBB is the target of a cbr, and
// we cannot reverse the branch.
- std::vector<MachineOperand> NewCond(Cond);
+ SmallVector<MachineOperand, 4> NewCond(Cond);
if (!Cond.empty() && TBB==IBB) {
if (TII->ReverseBranchCondition(NewCond))
continue;
if (MergePotentials.size() >= 2)
MadeChange |= TryMergeBlocks(I, PredBB);
// Reinsert an unconditional branch if needed.
- // The 1 below can be either an original single predecessor, or a result
- // of removing blocks in TryMergeBlocks.
+ // The 1 below can occur as a result of removing blocks in TryMergeBlocks.
PredBB = prior(I); // this may have been changed in TryMergeBlocks
if (MergePotentials.size()==1 &&
- (MergePotentials.begin())->second != PredBB)
- FixTail((MergePotentials.begin())->second, I, TII);
+ MergePotentials.begin()->second != PredBB)
+ FixTail(MergePotentials.begin()->second, I, TII);
}
}
return MadeChange;
///
bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB,
bool BranchUnAnalyzable,
- MachineBasicBlock *TBB, MachineBasicBlock *FBB,
- const std::vector<MachineOperand> &Cond) {
+ MachineBasicBlock *TBB,
+ MachineBasicBlock *FBB,
+ const SmallVectorImpl<MachineOperand> &Cond) {
MachineFunction::iterator Fallthrough = CurBB;
++Fallthrough;
// If FallthroughBlock is off the end of the function, it can't fall through.
///
bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) {
MachineBasicBlock *TBB = 0, *FBB = 0;
- std::vector<MachineOperand> Cond;
+ SmallVector<MachineOperand, 4> Cond;
bool CurUnAnalyzable = TII->AnalyzeBranch(*CurBB, TBB, FBB, Cond);
return CanFallThrough(CurBB, CurUnAnalyzable, TBB, FBB, Cond);
}
MachineBasicBlock &PrevBB = *prior(MachineFunction::iterator(MBB));
MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
- std::vector<MachineOperand> PriorCond;
+ SmallVector<MachineOperand, 4> PriorCond;
bool PriorUnAnalyzable =
TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond);
if (!PriorUnAnalyzable) {
// if the branch condition is reversible, reverse the branch to create a
// fall-through.
if (PriorTBB == MBB) {
- std::vector<MachineOperand> NewPriorCond(PriorCond);
+ SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
if (!TII->ReverseBranchCondition(NewPriorCond)) {
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond);
if (DoTransform) {
// Reverse the branch so we will fall through on the previous true cond.
- std::vector<MachineOperand> NewPriorCond(PriorCond);
+ SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
if (!TII->ReverseBranchCondition(NewPriorCond)) {
DOUT << "\nMoving MBB: " << *MBB;
DOUT << "To make fallthrough to: " << *PriorTBB << "\n";
// Analyze the branch in the current block.
MachineBasicBlock *CurTBB = 0, *CurFBB = 0;
- std::vector<MachineOperand> CurCond;
+ SmallVector<MachineOperand, 4> CurCond;
bool CurUnAnalyzable = TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond);
if (!CurUnAnalyzable) {
// If the CFG for the prior block has extra edges, remove them.
// we want:
// Loop: xxx; jncc Loop; jmp Out
if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
- std::vector<MachineOperand> NewCond(CurCond);
+ SmallVector<MachineOperand, 4> NewCond(CurCond);
if (!TII->ReverseBranchCondition(NewCond)) {
TII->RemoveBranch(*MBB);
TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond);
projects / oota-llvm.git / blobdiff