// Avoid emitting unnecessary branches to the next block.
if (MBB != NextBlock(SwitchBB))
- BrRange = DAG.getNode(ISD::BR, getCurSDLoc(), MVT::Other, CopyTo,
+ BrRange = DAG.getNode(ISD::BR, getCurSDLoc(), MVT::Other, BrRange,
DAG.getBasicBlock(MBB));
DAG.setRoot(BrRange);
return VReg;
}
-/// handleSmallSwitchCaseRange - Emit a series of specific tests (suitable for
-/// small case ranges).
-bool SelectionDAGBuilder::handleSmallSwitchRange(CaseRec& CR,
- CaseRecVector& WorkList,
- const Value* SV,
- MachineBasicBlock *Default,
- MachineBasicBlock *SwitchBB) {
- // Size is the number of Cases represented by this range.
- size_t Size = CR.Range.second - CR.Range.first;
- if (Size > 3)
- return false;
-
- // Get the MachineFunction which holds the current MBB. This is used when
- // inserting any additional MBBs necessary to represent the switch.
- MachineFunction *CurMF = FuncInfo.MF;
-
- // Figure out which block is immediately after the current one.
- MachineBasicBlock *NextMBB = nullptr;
- MachineFunction::iterator BBI = CR.CaseBB;
- if (++BBI != FuncInfo.MF->end())
- NextMBB = BBI;
-
- BranchProbabilityInfo *BPI = FuncInfo.BPI;
- // If any two of the cases has the same destination, and if one value
- // is the same as the other, but has one bit unset that the other has set,
- // use bit manipulation to do two compares at once. For example:
- // "if (X == 6 || X == 4)" -> "if ((X|2) == 6)"
- // TODO: This could be extended to merge any 2 cases in switches with 3 cases.
- // TODO: Handle cases where CR.CaseBB != SwitchBB.
- if (Size == 2 && CR.CaseBB == SwitchBB) {
- Case &Small = *CR.Range.first;
- Case &Big = *(CR.Range.second-1);
-
- if (Small.Low == Small.High && Big.Low == Big.High && Small.BB == Big.BB) {
- const APInt& SmallValue = Small.Low->getValue();
- const APInt& BigValue = Big.Low->getValue();
-
- // Check that there is only one bit different.
- if (BigValue.countPopulation() == SmallValue.countPopulation() + 1 &&
- (SmallValue | BigValue) == BigValue) {
- // Isolate the common bit.
- APInt CommonBit = BigValue & ~SmallValue;
- assert((SmallValue | CommonBit) == BigValue &&
- CommonBit.countPopulation() == 1 && "Not a common bit?");
-
- SDValue CondLHS = getValue(SV);
- EVT VT = CondLHS.getValueType();
- SDLoc DL = getCurSDLoc();
-
- SDValue Or = DAG.getNode(ISD::OR, DL, VT, CondLHS,
- DAG.getConstant(CommonBit, VT));
- SDValue Cond = DAG.getSetCC(DL, MVT::i1,
- Or, DAG.getConstant(BigValue, VT),
- ISD::SETEQ);
-
- // Update successor info.
- // Both Small and Big will jump to Small.BB, so we sum up the weights.
- addSuccessorWithWeight(SwitchBB, Small.BB,
- Small.ExtraWeight + Big.ExtraWeight);
- addSuccessorWithWeight(SwitchBB, Default,
- // The default destination is the first successor in IR.
- BPI ? BPI->getEdgeWeight(SwitchBB->getBasicBlock(), (unsigned)0) : 0);
-
- // Insert the true branch.
- SDValue BrCond = DAG.getNode(ISD::BRCOND, DL, MVT::Other,
- getControlRoot(), Cond,
- DAG.getBasicBlock(Small.BB));
-
- // Insert the false branch.
- BrCond = DAG.getNode(ISD::BR, DL, MVT::Other, BrCond,
- DAG.getBasicBlock(Default));
-
- DAG.setRoot(BrCond);
- return true;
- }
- }
- }
-
- // Order cases by weight so the most likely case will be checked first.
- uint32_t UnhandledWeights = 0;
- if (BPI) {
- for (CaseItr I = CR.Range.first, IE = CR.Range.second; I != IE; ++I) {
- uint32_t IWeight = I->ExtraWeight;
- UnhandledWeights += IWeight;
- for (CaseItr J = CR.Range.first; J < I; ++J) {
- uint32_t JWeight = J->ExtraWeight;
- if (IWeight > JWeight)
- std::swap(*I, *J);
- }
- }
- }
- // Rearrange the case blocks so that the last one falls through if possible.
- Case &BackCase = *(CR.Range.second-1);
- if (Size > 1 && NextMBB && Default != NextMBB && BackCase.BB != NextMBB) {
- // The last case block won't fall through into 'NextMBB' if we emit the
- // branches in this order. See if rearranging a case value would help.
- // We start at the bottom as it's the case with the least weight.
- for (Case *I = &*(CR.Range.second-2), *E = &*CR.Range.first-1; I != E; --I)
- if (I->BB == NextMBB) {
- std::swap(*I, BackCase);
- break;
- }
- }
-
- // Create a CaseBlock record representing a conditional branch to
- // the Case's target mbb if the value being switched on SV is equal
- // to C.
- MachineBasicBlock *CurBlock = CR.CaseBB;
- for (CaseItr I = CR.Range.first, E = CR.Range.second; I != E; ++I) {
- MachineBasicBlock *FallThrough;
- if (I != E-1) {
- FallThrough = CurMF->CreateMachineBasicBlock(CurBlock->getBasicBlock());
- CurMF->insert(BBI, FallThrough);
-
- // Put SV in a virtual register to make it available from the new blocks.
- ExportFromCurrentBlock(SV);
- } else {
- // If the last case doesn't match, go to the default block.
- FallThrough = Default;
- }
-
- const Value *RHS, *LHS, *MHS;
- ISD::CondCode CC;
- if (I->High == I->Low) {
- // This is just small small case range :) containing exactly 1 case
- CC = ISD::SETEQ;
- LHS = SV; RHS = I->High; MHS = nullptr;
- } else {
- CC = ISD::SETLE;
- LHS = I->Low; MHS = SV; RHS = I->High;
- }
-
- // The false weight should be sum of all un-handled cases.
- UnhandledWeights -= I->ExtraWeight;
- CaseBlock CB(CC, LHS, RHS, MHS, /* truebb */ I->BB, /* falsebb */ FallThrough,
- /* me */ CurBlock,
- /* trueweight */ I->ExtraWeight,
- /* falseweight */ UnhandledWeights);
-
- // If emitting the first comparison, just call visitSwitchCase to emit the
- // code into the current block. Otherwise, push the CaseBlock onto the
- // vector to be later processed by SDISel, and insert the node's MBB
- // before the next MBB.
- if (CurBlock == SwitchBB)
- visitSwitchCase(CB, SwitchBB);
- else
- SwitchCases.push_back(CB);
-
- CurBlock = FallThrough;
- }
-
- return true;
-}
-
-static inline bool areJTsAllowed(const TargetLowering &TLI) {
- return TLI.isOperationLegalOrCustom(ISD::BR_JT, MVT::Other) ||
- TLI.isOperationLegalOrCustom(ISD::BRIND, MVT::Other);
-}
-
-static APInt ComputeRange(const APInt &First, const APInt &Last) {
- uint32_t BitWidth = std::max(Last.getBitWidth(), First.getBitWidth()) + 1;
- APInt LastExt = Last.sext(BitWidth), FirstExt = First.sext(BitWidth);
- return (LastExt - FirstExt + 1ULL);
-}
-
-/// handleJTSwitchCase - Emit jumptable for current switch case range
-bool SelectionDAGBuilder::handleJTSwitchCase(CaseRec &CR,
- CaseRecVector &WorkList,
- const Value *SV,
- MachineBasicBlock *Default,
- MachineBasicBlock *SwitchBB) {
- Case& FrontCase = *CR.Range.first;
- Case& BackCase = *(CR.Range.second-1);
-
- const APInt &First = FrontCase.Low->getValue();
- const APInt &Last = BackCase.High->getValue();
-
- APInt TSize(First.getBitWidth(), 0);
- for (CaseItr I = CR.Range.first, E = CR.Range.second; I != E; ++I)
- TSize += I->size();
-
- const TargetLowering &TLI = DAG.getTargetLoweringInfo();
- if (!areJTsAllowed(TLI) || TSize.ult(TLI.getMinimumJumpTableEntries()))
- return false;
-
- APInt Range = ComputeRange(First, Last);
- // The density is TSize / Range. Require at least 40%.
- // It should not be possible for IntTSize to saturate for sane code, but make
- // sure we handle Range saturation correctly.
- uint64_t IntRange = Range.getLimitedValue(UINT64_MAX/10);
- uint64_t IntTSize = TSize.getLimitedValue(UINT64_MAX/10);
- if (IntTSize * 10 < IntRange * 4)
- return false;
-
- DEBUG(dbgs() << "Lowering jump table\n"
- << "First entry: " << First << ". Last entry: " << Last << '\n'
- << "Range: " << Range << ". Size: " << TSize << ".\n\n");
-
- // Get the MachineFunction which holds the current MBB. This is used when
- // inserting any additional MBBs necessary to represent the switch.
- MachineFunction *CurMF = FuncInfo.MF;
-
- // Figure out which block is immediately after the current one.
- MachineFunction::iterator BBI = CR.CaseBB;
- ++BBI;
-
- const BasicBlock *LLVMBB = CR.CaseBB->getBasicBlock();
-
- // Create a new basic block to hold the code for loading the address
- // of the jump table, and jumping to it. Update successor information;
- // we will either branch to the default case for the switch, or the jump
- // table.
- MachineBasicBlock *JumpTableBB = CurMF->CreateMachineBasicBlock(LLVMBB);
- CurMF->insert(BBI, JumpTableBB);
-
- addSuccessorWithWeight(CR.CaseBB, Default);
- addSuccessorWithWeight(CR.CaseBB, JumpTableBB);
-
- // Build a vector of destination BBs, corresponding to each target
- // of the jump table. If the value of the jump table slot corresponds to
- // a case statement, push the case's BB onto the vector, otherwise, push
- // the default BB.
- std::vector<MachineBasicBlock*> DestBBs;
- APInt TEI = First;
- for (CaseItr I = CR.Range.first, E = CR.Range.second; I != E; ++TEI) {
- const APInt &Low = I->Low->getValue();
- const APInt &High = I->High->getValue();
-
- if (Low.sle(TEI) && TEI.sle(High)) {
- DestBBs.push_back(I->BB);
- if (TEI==High)
- ++I;
- } else {
- DestBBs.push_back(Default);
- }
- }
-
- // Calculate weight for each unique destination in CR.
- DenseMap<MachineBasicBlock*, uint32_t> DestWeights;
- if (FuncInfo.BPI) {
- for (CaseItr I = CR.Range.first, E = CR.Range.second; I != E; ++I)
- DestWeights[I->BB] += I->ExtraWeight;
- }
-
- // Update successor info. Add one edge to each unique successor.
- BitVector SuccsHandled(CR.CaseBB->getParent()->getNumBlockIDs());
- for (MachineBasicBlock *DestBB : DestBBs) {
- if (!SuccsHandled[DestBB->getNumber()]) {
- SuccsHandled[DestBB->getNumber()] = true;
- auto I = DestWeights.find(DestBB);
- addSuccessorWithWeight(JumpTableBB, DestBB,
- I != DestWeights.end() ? I->second : 0);
- }
- }
-
- // Create a jump table index for this jump table.
- unsigned JTEncoding = TLI.getJumpTableEncoding();
- unsigned JTI = CurMF->getOrCreateJumpTableInfo(JTEncoding)
- ->createJumpTableIndex(DestBBs);
-
- // Set the jump table information so that we can codegen it as a second
- // MachineBasicBlock
- JumpTable JT(-1U, JTI, JumpTableBB, Default);
- JumpTableHeader JTH(First, Last, SV, CR.CaseBB, (CR.CaseBB == SwitchBB));
- if (CR.CaseBB == SwitchBB)
- visitJumpTableHeader(JT, JTH, SwitchBB);
-
- JTCases.push_back(JumpTableBlock(JTH, JT));
- return true;
-}
-
-/// handleBTSplitSwitchCase - emit comparison and split binary search tree into
-/// 2 subtrees.
-bool SelectionDAGBuilder::handleBTSplitSwitchCase(CaseRec& CR,
- CaseRecVector& WorkList,
- const Value* SV,
- MachineBasicBlock* SwitchBB) {
- Case& FrontCase = *CR.Range.first;
- Case& BackCase = *(CR.Range.second-1);
-
- // Size is the number of Cases represented by this range.
- unsigned Size = CR.Range.second - CR.Range.first;
-
- const APInt &First = FrontCase.Low->getValue();
- const APInt &Last = BackCase.High->getValue();
- double FMetric = 0;
- CaseItr Pivot = CR.Range.first + Size/2;
-
- // Select optimal pivot, maximizing sum density of LHS and RHS. This will
- // (heuristically) allow us to emit JumpTable's later.
- APInt TSize(First.getBitWidth(), 0);
- for (CaseItr I = CR.Range.first, E = CR.Range.second;
- I!=E; ++I)
- TSize += I->size();
-
- APInt LSize = FrontCase.size();
- APInt RSize = TSize-LSize;
- DEBUG(dbgs() << "Selecting best pivot: \n"
- << "First: " << First << ", Last: " << Last <<'\n'
- << "LSize: " << LSize << ", RSize: " << RSize << '\n');
- const TargetLowering &TLI = DAG.getTargetLoweringInfo();
- for (CaseItr I = CR.Range.first, J=I+1, E = CR.Range.second;
- J!=E; ++I, ++J) {
- const APInt &LEnd = I->High->getValue();
- const APInt &RBegin = J->Low->getValue();
- APInt Range = ComputeRange(LEnd, RBegin);
- assert((Range - 2ULL).isNonNegative() &&
- "Invalid case distance");
- // Use volatile double here to avoid excess precision issues on some hosts,
- // e.g. that use 80-bit X87 registers.
- // Only consider the density of sub-ranges that actually have sufficient
- // entries to be lowered as a jump table.
- volatile double LDensity =
- LSize.ult(TLI.getMinimumJumpTableEntries())
- ? 0.0
- : LSize.roundToDouble() / (LEnd - First + 1ULL).roundToDouble();
- volatile double RDensity =
- RSize.ult(TLI.getMinimumJumpTableEntries())
- ? 0.0
- : RSize.roundToDouble() / (Last - RBegin + 1ULL).roundToDouble();
- volatile double Metric = Range.logBase2() * (LDensity + RDensity);
- // Should always split in some non-trivial place
- DEBUG(dbgs() <<"=>Step\n"
- << "LEnd: " << LEnd << ", RBegin: " << RBegin << '\n'
- << "LDensity: " << LDensity
- << ", RDensity: " << RDensity << '\n'
- << "Metric: " << Metric << '\n');
- if (FMetric < Metric) {
- Pivot = J;
- FMetric = Metric;
- DEBUG(dbgs() << "Current metric set to: " << FMetric << '\n');
- }
-
- LSize += J->size();
- RSize -= J->size();
- }
-
- if (FMetric == 0 || !areJTsAllowed(TLI))
- Pivot = CR.Range.first + Size/2;
- splitSwitchCase(CR, Pivot, WorkList, SV, SwitchBB);
- return true;
-}
-
-void SelectionDAGBuilder::splitSwitchCase(CaseRec &CR, CaseItr Pivot,
- CaseRecVector &WorkList,
- const Value *SV,
- MachineBasicBlock *SwitchBB) {
- // Get the MachineFunction which holds the current MBB. This is used when
- // inserting any additional MBBs necessary to represent the switch.
- MachineFunction *CurMF = FuncInfo.MF;
-
- // Figure out which block is immediately after the current one.
- MachineFunction::iterator BBI = CR.CaseBB;
- ++BBI;
-
- const BasicBlock *LLVMBB = CR.CaseBB->getBasicBlock();
-
- CaseRange LHSR(CR.Range.first, Pivot);
- CaseRange RHSR(Pivot, CR.Range.second);
- const ConstantInt *C = Pivot->Low;
- MachineBasicBlock *FalseBB = nullptr, *TrueBB = nullptr;
-
- // We know that we branch to the LHS if the Value being switched on is
- // less than the Pivot value, C. We use this to optimize our binary
- // tree a bit, by recognizing that if SV is greater than or equal to the
- // LHS's Case Value, and that Case Value is exactly one less than the
- // Pivot's Value, then we can branch directly to the LHS's Target,
- // rather than creating a leaf node for it.
- if ((LHSR.second - LHSR.first) == 1 && LHSR.first->High == CR.GE &&
- C->getValue() == (CR.GE->getValue() + 1LL)) {
- TrueBB = LHSR.first->BB;
- } else {
- TrueBB = CurMF->CreateMachineBasicBlock(LLVMBB);
- CurMF->insert(BBI, TrueBB);
- WorkList.push_back(CaseRec(TrueBB, C, CR.GE, LHSR));
-
- // Put SV in a virtual register to make it available from the new blocks.
- ExportFromCurrentBlock(SV);
- }
-
- // Similar to the optimization above, if the Value being switched on is
- // known to be less than the Constant CR.LT, and the current Case Value
- // is CR.LT - 1, then we can branch directly to the target block for
- // the current Case Value, rather than emitting a RHS leaf node for it.
- if ((RHSR.second - RHSR.first) == 1 && CR.LT &&
- RHSR.first->Low->getValue() == (CR.LT->getValue() - 1LL)) {
- FalseBB = RHSR.first->BB;
- } else {
- FalseBB = CurMF->CreateMachineBasicBlock(LLVMBB);
- CurMF->insert(BBI, FalseBB);
- WorkList.push_back(CaseRec(FalseBB, CR.LT, C, RHSR));
-
- // Put SV in a virtual register to make it available from the new blocks.
- ExportFromCurrentBlock(SV);
- }
-
- // Create a CaseBlock record representing a conditional branch to
- // the LHS node if the value being switched on SV is less than C.
- // Otherwise, branch to LHS.
- CaseBlock CB(ISD::SETLT, SV, C, nullptr, TrueBB, FalseBB, CR.CaseBB);
-
- if (CR.CaseBB == SwitchBB)
- visitSwitchCase(CB, SwitchBB);
- else
- SwitchCases.push_back(CB);
-}
-
-/// handleBitTestsSwitchCase - if current case range has few destination and
-/// range span less, than machine word bitwidth, encode case range into series
-/// of masks and emit bit tests with these masks.
-bool SelectionDAGBuilder::handleBitTestsSwitchCase(CaseRec& CR,
- CaseRecVector& WorkList,
- const Value* SV,
- MachineBasicBlock* Default,
- MachineBasicBlock* SwitchBB) {
- const TargetLowering &TLI = DAG.getTargetLoweringInfo();
- EVT PTy = TLI.getPointerTy();
- unsigned IntPtrBits = PTy.getSizeInBits();
-
- Case& FrontCase = *CR.Range.first;
- Case& BackCase = *(CR.Range.second-1);
-
- // Get the MachineFunction which holds the current MBB. This is used when
- // inserting any additional MBBs necessary to represent the switch.
- MachineFunction *CurMF = FuncInfo.MF;
-
- // If target does not have legal shift left, do not emit bit tests at all.
- if (!TLI.isOperationLegal(ISD::SHL, PTy))
- return false;
-
- size_t numCmps = 0;
- for (CaseItr I = CR.Range.first, E = CR.Range.second; I != E; ++I) {
- // Single case counts one, case range - two.
- numCmps += (I->Low == I->High ? 1 : 2);
- }
-
- // Count unique destinations
- SmallSet<MachineBasicBlock*, 4> Dests;
- for (CaseItr I = CR.Range.first, E = CR.Range.second; I != E; ++I) {
- Dests.insert(I->BB);
- if (Dests.size() > 3)
- // Don't bother the code below, if there are too much unique destinations
- return false;
- }
- DEBUG(dbgs() << "Total number of unique destinations: "
- << Dests.size() << '\n'
- << "Total number of comparisons: " << numCmps << '\n');
-
- // Compute span of values.
- const APInt& minValue = FrontCase.Low->getValue();
- const APInt& maxValue = BackCase.High->getValue();
- APInt cmpRange = maxValue - minValue;
-
- DEBUG(dbgs() << "Compare range: " << cmpRange << '\n'
- << "Low bound: " << minValue << '\n'
- << "High bound: " << maxValue << '\n');
-
- if (cmpRange.uge(IntPtrBits) ||
- (!(Dests.size() == 1 && numCmps >= 3) &&
- !(Dests.size() == 2 && numCmps >= 5) &&
- !(Dests.size() >= 3 && numCmps >= 6)))
- return false;
-
- DEBUG(dbgs() << "Emitting bit tests\n");
- APInt lowBound = APInt::getNullValue(cmpRange.getBitWidth());
-
- // Optimize the case where all the case values fit in a
- // word without having to subtract minValue. In this case,
- // we can optimize away the subtraction.
- if (minValue.isNonNegative() && maxValue.slt(IntPtrBits)) {
- cmpRange = maxValue;
- } else {
- lowBound = minValue;
- }
-
- CaseBitsVector CasesBits;
- unsigned i, count = 0;
-
- for (CaseItr I = CR.Range.first, E = CR.Range.second; I!=E; ++I) {
- MachineBasicBlock* Dest = I->BB;
- for (i = 0; i < count; ++i)
- if (Dest == CasesBits[i].BB)
- break;
-
- if (i == count) {
- assert((count < 3) && "Too much destinations to test!");
- CasesBits.push_back(CaseBits(0, Dest, 0, 0/*Weight*/));
- count++;
- }
-
- const APInt& lowValue = I->Low->getValue();
- const APInt& highValue = I->High->getValue();
-
- uint64_t lo = (lowValue - lowBound).getZExtValue();
- uint64_t hi = (highValue - lowBound).getZExtValue();
- CasesBits[i].ExtraWeight += I->ExtraWeight;
-
- for (uint64_t j = lo; j <= hi; j++) {
- CasesBits[i].Mask |= 1ULL << j;
- CasesBits[i].Bits++;
- }
-
- }
- std::sort(CasesBits.begin(), CasesBits.end(), CaseBitsCmp());
-
- BitTestInfo BTC;
-
- // Figure out which block is immediately after the current one.
- MachineFunction::iterator BBI = CR.CaseBB;
- ++BBI;
-
- const BasicBlock *LLVMBB = CR.CaseBB->getBasicBlock();
-
- DEBUG(dbgs() << "Cases:\n");
- for (unsigned i = 0, e = CasesBits.size(); i!=e; ++i) {
- DEBUG(dbgs() << "Mask: " << CasesBits[i].Mask
- << ", Bits: " << CasesBits[i].Bits
- << ", BB: " << CasesBits[i].BB << '\n');
-
- MachineBasicBlock *CaseBB = CurMF->CreateMachineBasicBlock(LLVMBB);
- CurMF->insert(BBI, CaseBB);
- BTC.push_back(BitTestCase(CasesBits[i].Mask,
- CaseBB,
- CasesBits[i].BB, CasesBits[i].ExtraWeight));
-
- // Put SV in a virtual register to make it available from the new blocks.
- ExportFromCurrentBlock(SV);
- }
-
- BitTestBlock BTB(lowBound, cmpRange, SV,
- -1U, MVT::Other, (CR.CaseBB == SwitchBB),
- CR.CaseBB, Default, std::move(BTC));
-
- if (CR.CaseBB == SwitchBB)
- visitBitTestHeader(BTB, SwitchBB);
-
- BitTestCases.push_back(std::move(BTB));
-
- return true;
-}
-
-void SelectionDAGBuilder::Clusterify(CaseVector &Cases, const SwitchInst *SI) {
- BranchProbabilityInfo *BPI = FuncInfo.BPI;
+void SelectionDAGBuilder::sortAndRangeify(CaseClusterVector &Clusters) {
+#ifndef NDEBUG
+ for (const CaseCluster &CC : Clusters)
+ assert(CC.Low == CC.High && "Input clusters must be single-case");
+#endif
- // Extract cases from the switch and sort them.
- typedef std::pair<const ConstantInt*, unsigned> CasePair;
- std::vector<CasePair> Sorted;
- Sorted.reserve(SI->getNumCases());
- for (auto I : SI->cases())
- Sorted.push_back(std::make_pair(I.getCaseValue(), I.getSuccessorIndex()));
- std::sort(Sorted.begin(), Sorted.end(), [](CasePair a, CasePair b) {
- return a.first->getValue().slt(b.first->getValue());
+ std::sort(Clusters.begin(), Clusters.end(),
+ [](const CaseCluster &a, const CaseCluster &b) {
+ return a.Low->getValue().slt(b.Low->getValue());
});
- // Merge adjacent cases with the same destination, build Cases vector.
- assert(Cases.empty() && "Cases should be empty before Clusterify;");
- Cases.reserve(SI->getNumCases());
- MachineBasicBlock *PreviousSucc = nullptr;
- for (CasePair &CP : Sorted) {
- const ConstantInt *CaseVal = CP.first;
- unsigned SuccIndex = CP.second;
- MachineBasicBlock *Succ = FuncInfo.MBBMap[SI->getSuccessor(SuccIndex)];
- uint32_t Weight = BPI ? BPI->getEdgeWeight(SI->getParent(), SuccIndex) : 0;
-
- if (PreviousSucc == Succ &&
- (CaseVal->getValue() - Cases.back().High->getValue()) == 1) {
+ // Merge adjacent clusters with the same destination.
+ const unsigned N = Clusters.size();
+ unsigned DstIndex = 0;
+ for (unsigned SrcIndex = 0; SrcIndex < N; ++SrcIndex) {
+ CaseCluster &CC = Clusters[SrcIndex];
+ const ConstantInt *CaseVal = CC.Low;
+ MachineBasicBlock *Succ = CC.MBB;
+
+ if (DstIndex != 0 && Clusters[DstIndex - 1].MBB == Succ &&
+ (CaseVal->getValue() - Clusters[DstIndex - 1].High->getValue()) == 1) {
// If this case has the same successor and is a neighbour, merge it into
// the previous cluster.
- Cases.back().High = CaseVal;
- Cases.back().ExtraWeight += Weight;
+ Clusters[DstIndex - 1].High = CaseVal;
+ Clusters[DstIndex - 1].Weight += CC.Weight;
} else {
- Cases.push_back(Case(CaseVal, CaseVal, Succ, Weight));
+ std::memmove(&Clusters[DstIndex++], &Clusters[SrcIndex],
+ sizeof(Clusters[SrcIndex]));
}
-
- PreviousSucc = Succ;
}
-
- DEBUG({
- size_t numCmps = 0;
- for (auto &I : Cases)
- // A range counts double, since it requires two compares.
- numCmps += I.Low != I.High ? 2 : 1;
-
- dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
- << ". Total compares: " << numCmps << '\n';
- });
+ Clusters.resize(DstIndex);
}
void SelectionDAGBuilder::UpdateSplitBlock(MachineBasicBlock *First,
BitTestCases[i].Parent = Last;
}
-void SelectionDAGBuilder::visitSwitch(const SwitchInst &SI) {
- MachineBasicBlock *SwitchMBB = FuncInfo.MBB;
-
- // Create a vector of Cases, sorted so that we can efficiently create a binary
- // search tree from them.
- CaseVector Cases;
- Clusterify(Cases, &SI);
-
- // Get the default destination MBB.
- MachineBasicBlock *Default = FuncInfo.MBBMap[SI.getDefaultDest()];
-
- if (isa<UnreachableInst>(SI.getDefaultDest()->getFirstNonPHIOrDbg()) &&
- !Cases.empty()) {
- // Replace an unreachable default destination with the most popular case
- // destination.
- DenseMap<const BasicBlock *, unsigned> Popularity;
- unsigned MaxPop = 0;
- const BasicBlock *MaxBB = nullptr;
- for (auto I : SI.cases()) {
- const BasicBlock *BB = I.getCaseSuccessor();
- if (++Popularity[BB] > MaxPop) {
- MaxPop = Popularity[BB];
- MaxBB = BB;
- }
- }
-
- // Set new default.
- assert(MaxPop > 0);
- assert(MaxBB);
- Default = FuncInfo.MBBMap[MaxBB];
-
- // Remove cases that were pointing to the destination that is now the default.
- Cases.erase(std::remove_if(Cases.begin(), Cases.end(),
- [&](const Case &C) { return C.BB == Default; }),
- Cases.end());
- }
-
- // If there is only the default destination, go there directly.
- if (Cases.empty()) {
- // Update machine-CFG edges.
- SwitchMBB->addSuccessor(Default);
-
- // If this is not a fall-through branch, emit the branch.
- if (Default != NextBlock(SwitchMBB)) {
- DAG.setRoot(DAG.getNode(ISD::BR, getCurSDLoc(), MVT::Other,
- getControlRoot(), DAG.getBasicBlock(Default)));
- }
- return;
- }
-
- // Get the Value to be switched on.
- const Value *SV = SI.getCondition();
-
- // Push the initial CaseRec onto the worklist
- CaseRecVector WorkList;
- WorkList.push_back(CaseRec(SwitchMBB,nullptr,nullptr,
- CaseRange(Cases.begin(),Cases.end())));
-
- while (!WorkList.empty()) {
- // Grab a record representing a case range to process off the worklist
- CaseRec CR = WorkList.back();
- WorkList.pop_back();
-
- if (handleBitTestsSwitchCase(CR, WorkList, SV, Default, SwitchMBB))
- continue;
-
- // If the range has few cases (two or less) emit a series of specific
- // tests.
- if (handleSmallSwitchRange(CR, WorkList, SV, Default, SwitchMBB))
- continue;
-
- // If the switch has more than N blocks, and is at least 40% dense, and the
- // target supports indirect branches, then emit a jump table rather than
- // lowering the switch to a binary tree of conditional branches.
- // N defaults to 4 and is controlled via TLS.getMinimumJumpTableEntries().
- if (handleJTSwitchCase(CR, WorkList, SV, Default, SwitchMBB))
- continue;
-
- // Emit binary tree. We need to pick a pivot, and push left and right ranges
- // onto the worklist. Leafs are handled via handleSmallSwitchRange() call.
- handleBTSplitSwitchCase(CR, WorkList, SV, SwitchMBB);
- }
-}
-
void SelectionDAGBuilder::visitIndirectBr(const IndirectBrInst &I) {
MachineBasicBlock *IndirectBrMBB = FuncInfo.MBB;
HasTailCall = true;
}
+bool SelectionDAGBuilder::isDense(const CaseClusterVector &Clusters,
+ unsigned *TotalCases, unsigned First,
+ unsigned Last) {
+ assert(Last >= First);
+ assert(TotalCases[Last] >= TotalCases[First]);
+
+ APInt LowCase = Clusters[First].Low->getValue();
+ APInt HighCase = Clusters[Last].High->getValue();
+ assert(LowCase.getBitWidth() == HighCase.getBitWidth());
+
+ // FIXME: A range of consecutive cases has 100% density, but only requires one
+ // comparison to lower. We should discriminate against such consecutive ranges
+ // in jump tables.
+
+ uint64_t Diff = (HighCase - LowCase).getLimitedValue((UINT64_MAX - 1) / 100);
+ uint64_t Range = Diff + 1;
+
+ uint64_t NumCases =
+ TotalCases[Last] - (First == 0 ? 0 : TotalCases[First - 1]);
+
+ assert(NumCases < UINT64_MAX / 100);
+ assert(Range >= NumCases);
+
+ return NumCases * 100 >= Range * MinJumpTableDensity;
+}
+
+static inline bool areJTsAllowed(const TargetLowering &TLI) {
+ return TLI.isOperationLegalOrCustom(ISD::BR_JT, MVT::Other) ||
+ TLI.isOperationLegalOrCustom(ISD::BRIND, MVT::Other);
+}
+
+bool SelectionDAGBuilder::buildJumpTable(CaseClusterVector &Clusters,
+ unsigned First, unsigned Last,
+ const SwitchInst *SI,
+ MachineBasicBlock *DefaultMBB,
+ CaseCluster &JTCluster) {
+ assert(First <= Last);
+
+ uint64_t Weight = 0;
+ unsigned NumCmps = 0;
+ std::vector<MachineBasicBlock*> Table;
+ DenseMap<MachineBasicBlock*, uint32_t> JTWeights;
+ for (unsigned I = First; I <= Last; ++I) {
+ assert(Clusters[I].Kind == CC_Range);
+ Weight += Clusters[I].Weight;
+ APInt Low = Clusters[I].Low->getValue();
+ APInt High = Clusters[I].High->getValue();
+ NumCmps += (Low == High) ? 1 : 2;
+ if (I != First) {
+ // Fill the gap between this and the previous cluster.
+ APInt PreviousHigh = Clusters[I - 1].High->getValue();
+ assert(PreviousHigh.slt(Low));
+ uint64_t Gap = (Low - PreviousHigh).getLimitedValue() - 1;
+ for (uint64_t J = 0; J < Gap; J++)
+ Table.push_back(DefaultMBB);
+ }
+ for (APInt X = Low; X.sle(High); ++X)
+ Table.push_back(Clusters[I].MBB);
+ JTWeights[Clusters[I].MBB] += Clusters[I].Weight;
+ }
+
+ unsigned NumDests = JTWeights.size();
+ if (isSuitableForBitTests(NumDests, NumCmps,
+ Clusters[First].Low->getValue(),
+ Clusters[Last].High->getValue())) {
+ // Clusters[First..Last] should be lowered as bit tests instead.
+ return false;
+ }
+
+ // Create the MBB that will load from and jump through the table.
+ // Note: We create it here, but it's not inserted into the function yet.
+ MachineFunction *CurMF = FuncInfo.MF;
+ MachineBasicBlock *JumpTableMBB =
+ CurMF->CreateMachineBasicBlock(SI->getParent());
+
+ // Add successors. Note: use table order for determinism.
+ SmallPtrSet<MachineBasicBlock *, 8> Done;
+ for (MachineBasicBlock *Succ : Table) {
+ if (Done.count(Succ))
+ continue;
+ addSuccessorWithWeight(JumpTableMBB, Succ, JTWeights[Succ]);
+ Done.insert(Succ);
+ }
+
+ const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+ unsigned JTI = CurMF->getOrCreateJumpTableInfo(TLI.getJumpTableEncoding())
+ ->createJumpTableIndex(Table);
+
+ // Set up the jump table info.
+ JumpTable JT(-1U, JTI, JumpTableMBB, nullptr);
+ JumpTableHeader JTH(Clusters[First].Low->getValue(),
+ Clusters[Last].High->getValue(), SI->getCondition(),
+ nullptr, false);
+ JTCases.push_back(JumpTableBlock(JTH, JT));
+
+ JTCluster = CaseCluster::jumpTable(Clusters[First].Low, Clusters[Last].High,
+ JTCases.size() - 1, Weight);
+ return true;
+}
+
+void SelectionDAGBuilder::findJumpTables(CaseClusterVector &Clusters,
+ const SwitchInst *SI,
+ MachineBasicBlock *DefaultMBB) {
+#ifndef NDEBUG
+ // Clusters must be non-empty, sorted, and only contain Range clusters.
+ assert(!Clusters.empty());
+ for (CaseCluster &C : Clusters)
+ assert(C.Kind == CC_Range);
+ for (unsigned i = 1, e = Clusters.size(); i < e; ++i)
+ assert(Clusters[i - 1].High->getValue().slt(Clusters[i].Low->getValue()));
+#endif
+
+ const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+ if (!areJTsAllowed(TLI))
+ return;
+
+ const int64_t N = Clusters.size();
+ const unsigned MinJumpTableSize = TLI.getMinimumJumpTableEntries();
+
+ // Split Clusters into minimum number of dense partitions. The algorithm uses
+ // the same idea as Kannan & Proebsting "Correction to 'Producing Good Code
+ // for the Case Statement'" (1994), but builds the MinPartitions array in
+ // reverse order to make it easier to reconstruct the partitions in ascending
+ // order. In the choice between two optimal partitionings, it picks the one
+ // which yields more jump tables.
+
+ // MinPartitions[i] is the minimum nbr of partitions of Clusters[i..N-1].
+ SmallVector<unsigned, 8> MinPartitions(N);
+ // LastElement[i] is the last element of the partition starting at i.
+ SmallVector<unsigned, 8> LastElement(N);
+ // NumTables[i]: nbr of >= MinJumpTableSize partitions from Clusters[i..N-1].
+ SmallVector<unsigned, 8> NumTables(N);
+ // TotalCases[i]: Total nbr of cases in Clusters[0..i].
+ SmallVector<unsigned, 8> TotalCases(N);
+
+ for (unsigned i = 0; i < N; ++i) {
+ APInt Hi = Clusters[i].High->getValue();
+ APInt Lo = Clusters[i].Low->getValue();
+ TotalCases[i] = (Hi - Lo).getLimitedValue() + 1;
+ if (i != 0)
+ TotalCases[i] += TotalCases[i - 1];
+ }
+
+ // Base case: There is only one way to partition Clusters[N-1].
+ MinPartitions[N - 1] = 1;
+ LastElement[N - 1] = N - 1;
+ assert(MinJumpTableSize > 1);
+ NumTables[N - 1] = 0;
+
+ // Note: loop indexes are signed to avoid underflow.
+ for (int64_t i = N - 2; i >= 0; i--) {
+ // Find optimal partitioning of Clusters[i..N-1].
+ // Baseline: Put Clusters[i] into a partition on its own.
+ MinPartitions[i] = MinPartitions[i + 1] + 1;
+ LastElement[i] = i;
+ NumTables[i] = NumTables[i + 1];
+
+ // Search for a solution that results in fewer partitions.
+ for (int64_t j = N - 1; j > i; j--) {
+ // Try building a partition from Clusters[i..j].
+ if (isDense(Clusters, &TotalCases[0], i, j)) {
+ unsigned NumPartitions = 1 + (j == N - 1 ? 0 : MinPartitions[j + 1]);
+ bool IsTable = j - i + 1 >= MinJumpTableSize;
+ unsigned Tables = IsTable + (j == N - 1 ? 0 : NumTables[j + 1]);
+
+ // If this j leads to fewer partitions, or same number of partitions
+ // with more lookup tables, it is a better partitioning.
+ if (NumPartitions < MinPartitions[i] ||
+ (NumPartitions == MinPartitions[i] && Tables > NumTables[i])) {
+ MinPartitions[i] = NumPartitions;
+ LastElement[i] = j;
+ NumTables[i] = Tables;
+ }
+ }
+ }
+ }
+
+ // Iterate over the partitions, replacing some with jump tables in-place.
+ unsigned DstIndex = 0;
+ for (unsigned First = 0, Last; First < N; First = Last + 1) {
+ Last = LastElement[First];
+ assert(Last >= First);
+ assert(DstIndex <= First);
+ unsigned NumClusters = Last - First + 1;
+
+ CaseCluster JTCluster;
+ if (NumClusters >= MinJumpTableSize &&
+ buildJumpTable(Clusters, First, Last, SI, DefaultMBB, JTCluster)) {
+ Clusters[DstIndex++] = JTCluster;
+ } else {
+ for (unsigned I = First; I <= Last; ++I)
+ std::memmove(&Clusters[DstIndex++], &Clusters[I], sizeof(Clusters[I]));
+ }
+ }
+ Clusters.resize(DstIndex);
+}
+
+bool SelectionDAGBuilder::rangeFitsInWord(const APInt &Low, const APInt &High) {
+ // FIXME: Using the pointer type doesn't seem ideal.
+ uint64_t BW = DAG.getTargetLoweringInfo().getPointerTy().getSizeInBits();
+ uint64_t Range = (High - Low).getLimitedValue(UINT64_MAX - 1) + 1;
+ return Range <= BW;
+}
+
+bool SelectionDAGBuilder::isSuitableForBitTests(unsigned NumDests,
+ unsigned NumCmps,
+ const APInt &Low,
+ const APInt &High) {
+ // FIXME: I don't think NumCmps is the correct metric: a single case and a
+ // range of cases both require only one branch to lower. Just looking at the
+ // number of clusters and destinations should be enough to decide whether to
+ // build bit tests.
+
+ // To lower a range with bit tests, the range must fit the bitwidth of a
+ // machine word.
+ if (!rangeFitsInWord(Low, High))
+ return false;
+
+ // Decide whether it's profitable to lower this range with bit tests. Each
+ // destination requires a bit test and branch, and there is an overall range
+ // check branch. For a small number of clusters, separate comparisons might be
+ // cheaper, and for many destinations, splitting the range might be better.
+ return (NumDests == 1 && NumCmps >= 3) ||
+ (NumDests == 2 && NumCmps >= 5) ||
+ (NumDests == 3 && NumCmps >= 6);
+}
+
+bool SelectionDAGBuilder::buildBitTests(CaseClusterVector &Clusters,
+ unsigned First, unsigned Last,
+ const SwitchInst *SI,
+ CaseCluster &BTCluster) {
+ assert(First <= Last);
+ if (First == Last)
+ return false;
+
+ BitVector Dests(FuncInfo.MF->getNumBlockIDs());
+ unsigned NumCmps = 0;
+ for (int64_t I = First; I <= Last; ++I) {
+ assert(Clusters[I].Kind == CC_Range);
+ Dests.set(Clusters[I].MBB->getNumber());
+ NumCmps += (Clusters[I].Low == Clusters[I].High) ? 1 : 2;
+ }
+ unsigned NumDests = Dests.count();
+
+ APInt Low = Clusters[First].Low->getValue();
+ APInt High = Clusters[Last].High->getValue();
+ assert(Low.slt(High));
+
+ if (!isSuitableForBitTests(NumDests, NumCmps, Low, High))
+ return false;
+
+ APInt LowBound;
+ APInt CmpRange;
+
+ const int BitWidth =
+ DAG.getTargetLoweringInfo().getPointerTy().getSizeInBits();
+ assert((High - Low + 1).sle(BitWidth) && "Case range must fit in bit mask!");
+
+ if (Low.isNonNegative() && High.slt(BitWidth)) {
+ // Optimize the case where all the case values fit in a
+ // word without having to subtract minValue. In this case,
+ // we can optimize away the subtraction.
+ LowBound = APInt::getNullValue(Low.getBitWidth());
+ CmpRange = High;
+ } else {
+ LowBound = Low;
+ CmpRange = High - Low;
+ }
+
+ CaseBitsVector CBV;
+ uint64_t TotalWeight = 0;
+ for (unsigned i = First; i <= Last; ++i) {
+ // Find the CaseBits for this destination.
+ unsigned j;
+ for (j = 0; j < CBV.size(); ++j)
+ if (CBV[j].BB == Clusters[i].MBB)
+ break;
+ if (j == CBV.size())
+ CBV.push_back(CaseBits(0, Clusters[i].MBB, 0, 0));
+ CaseBits *CB = &CBV[j];
+
+ // Update Mask, Bits and ExtraWeight.
+ uint64_t Lo = (Clusters[i].Low->getValue() - LowBound).getZExtValue();
+ uint64_t Hi = (Clusters[i].High->getValue() - LowBound).getZExtValue();
+ for (uint64_t j = Lo; j <= Hi; ++j) {
+ CB->Mask |= 1ULL << j;
+ CB->Bits++;
+ }
+ CB->ExtraWeight += Clusters[i].Weight;
+ TotalWeight += Clusters[i].Weight;
+ }
+
+ BitTestInfo BTI;
+ std::sort(CBV.begin(), CBV.end(), [](const CaseBits &a, const CaseBits &b) {
+ // FIXME: Sort by weight.
+ return a.Bits > b.Bits;
+ });
+
+ for (auto &CB : CBV) {
+ MachineBasicBlock *BitTestBB =
+ FuncInfo.MF->CreateMachineBasicBlock(SI->getParent());
+ BTI.push_back(BitTestCase(CB.Mask, BitTestBB, CB.BB, CB.ExtraWeight));
+ }
+ BitTestCases.push_back(BitTestBlock(LowBound, CmpRange, SI->getCondition(),
+ -1U, MVT::Other, false, nullptr,
+ nullptr, std::move(BTI)));
+
+ BTCluster = CaseCluster::bitTests(Clusters[First].Low, Clusters[Last].High,
+ BitTestCases.size() - 1, TotalWeight);
+ return true;
+}
+
+void SelectionDAGBuilder::findBitTestClusters(CaseClusterVector &Clusters,
+ const SwitchInst *SI) {
+// Partition Clusters into as few subsets as possible, where each subset has a
+// range that fits in a machine word and has <= 3 unique destinations.
+
+#ifndef NDEBUG
+ // Clusters must be sorted and contain Range or JumpTable clusters.
+ assert(!Clusters.empty());
+ assert(Clusters[0].Kind == CC_Range || Clusters[0].Kind == CC_JumpTable);
+ for (const CaseCluster &C : Clusters)
+ assert(C.Kind == CC_Range || C.Kind == CC_JumpTable);
+ for (unsigned i = 1; i < Clusters.size(); ++i)
+ assert(Clusters[i-1].High->getValue().slt(Clusters[i].Low->getValue()));
+#endif
+
+ // If target does not have legal shift left, do not emit bit tests at all.
+ const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+ EVT PTy = TLI.getPointerTy();
+ if (!TLI.isOperationLegal(ISD::SHL, PTy))
+ return;
+
+ int BitWidth = PTy.getSizeInBits();
+ const int64_t N = Clusters.size();
+
+ // MinPartitions[i] is the minimum nbr of partitions of Clusters[i..N-1].
+ SmallVector<unsigned, 8> MinPartitions(N);
+ // LastElement[i] is the last element of the partition starting at i.
+ SmallVector<unsigned, 8> LastElement(N);
+
+ // FIXME: This might not be the best algorithm for finding bit test clusters.
+
+ // Base case: There is only one way to partition Clusters[N-1].
+ MinPartitions[N - 1] = 1;
+ LastElement[N - 1] = N - 1;
+
+ // Note: loop indexes are signed to avoid underflow.
+ for (int64_t i = N - 2; i >= 0; --i) {
+ // Find optimal partitioning of Clusters[i..N-1].
+ // Baseline: Put Clusters[i] into a partition on its own.
+ MinPartitions[i] = MinPartitions[i + 1] + 1;
+ LastElement[i] = i;
+
+ // Search for a solution that results in fewer partitions.
+ // Note: the search is limited by BitWidth, reducing time complexity.
+ for (int64_t j = std::min(N - 1, i + BitWidth - 1); j > i; --j) {
+ // Try building a partition from Clusters[i..j].
+
+ // Check the range.
+ if (!rangeFitsInWord(Clusters[i].Low->getValue(),
+ Clusters[j].High->getValue()))
+ continue;
+
+ // Check nbr of destinations and cluster types.
+ // FIXME: This works, but doesn't seem very efficient.
+ bool RangesOnly = true;
+ BitVector Dests(FuncInfo.MF->getNumBlockIDs());
+ for (int64_t k = i; k <= j; k++) {
+ if (Clusters[k].Kind != CC_Range) {
+ RangesOnly = false;
+ break;
+ }
+ Dests.set(Clusters[k].MBB->getNumber());
+ }
+ if (!RangesOnly || Dests.count() > 3)
+ break;
+
+ // Check if it's a better partition.
+ unsigned NumPartitions = 1 + (j == N - 1 ? 0 : MinPartitions[j + 1]);
+ if (NumPartitions < MinPartitions[i]) {
+ // Found a better partition.
+ MinPartitions[i] = NumPartitions;
+ LastElement[i] = j;
+ }
+ }
+ }
+
+ // Iterate over the partitions, replacing with bit-test clusters in-place.
+ unsigned DstIndex = 0;
+ for (unsigned First = 0, Last; First < N; First = Last + 1) {
+ Last = LastElement[First];
+ assert(First <= Last);
+ assert(DstIndex <= First);
+
+ CaseCluster BitTestCluster;
+ if (buildBitTests(Clusters, First, Last, SI, BitTestCluster)) {
+ Clusters[DstIndex++] = BitTestCluster;
+ } else {
+ for (unsigned I = First; I <= Last; ++I)
+ std::memmove(&Clusters[DstIndex++], &Clusters[I], sizeof(Clusters[I]));
+ }
+ }
+ Clusters.resize(DstIndex);
+}
+
+void SelectionDAGBuilder::lowerWorkItem(SwitchWorkListItem W, Value *Cond,
+ MachineBasicBlock *SwitchMBB,
+ MachineBasicBlock *DefaultMBB) {
+ MachineFunction *CurMF = FuncInfo.MF;
+ MachineBasicBlock *NextMBB = nullptr;
+ MachineFunction::iterator BBI = W.MBB;
+ if (++BBI != FuncInfo.MF->end())
+ NextMBB = BBI;
+
+ unsigned Size = W.LastCluster - W.FirstCluster + 1;
+
+ BranchProbabilityInfo *BPI = FuncInfo.BPI;
+
+ if (Size == 2 && W.MBB == SwitchMBB) {
+ // If any two of the cases has the same destination, and if one value
+ // is the same as the other, but has one bit unset that the other has set,
+ // use bit manipulation to do two compares at once. For example:
+ // "if (X == 6 || X == 4)" -> "if ((X|2) == 6)"
+ // TODO: This could be extended to merge any 2 cases in switches with 3
+ // cases.
+ // TODO: Handle cases where W.CaseBB != SwitchBB.
+ CaseCluster &Small = *W.FirstCluster;
+ CaseCluster &Big = *W.LastCluster;
+
+ if (Small.Low == Small.High && Big.Low == Big.High &&
+ Small.MBB == Big.MBB) {
+ const APInt &SmallValue = Small.Low->getValue();
+ const APInt &BigValue = Big.Low->getValue();
+
+ // Check that there is only one bit different.
+ if (BigValue.countPopulation() == SmallValue.countPopulation() + 1 &&
+ (SmallValue | BigValue) == BigValue) {
+ // Isolate the common bit.
+ APInt CommonBit = BigValue & ~SmallValue;
+ assert((SmallValue | CommonBit) == BigValue &&
+ CommonBit.countPopulation() == 1 && "Not a common bit?");
+
+ SDValue CondLHS = getValue(Cond);
+ EVT VT = CondLHS.getValueType();
+ SDLoc DL = getCurSDLoc();
+
+ SDValue Or = DAG.getNode(ISD::OR, DL, VT, CondLHS,
+ DAG.getConstant(CommonBit, VT));
+ SDValue Cond = DAG.getSetCC(DL, MVT::i1, Or,
+ DAG.getConstant(BigValue, VT), ISD::SETEQ);
+
+ // Update successor info.
+ // Both Small and Big will jump to Small.BB, so we sum up the weights.
+ addSuccessorWithWeight(SwitchMBB, Small.MBB, Small.Weight + Big.Weight);
+ addSuccessorWithWeight(
+ SwitchMBB, DefaultMBB,
+ // The default destination is the first successor in IR.
+ BPI ? BPI->getEdgeWeight(SwitchMBB->getBasicBlock(), (unsigned)0)
+ : 0);
+
+ // Insert the true branch.
+ SDValue BrCond =
+ DAG.getNode(ISD::BRCOND, DL, MVT::Other, getControlRoot(), Cond,
+ DAG.getBasicBlock(Small.MBB));
+ // Insert the false branch.
+ BrCond = DAG.getNode(ISD::BR, DL, MVT::Other, BrCond,
+ DAG.getBasicBlock(DefaultMBB));
+
+ DAG.setRoot(BrCond);
+ return;
+ }
+ }
+ }
+
+ if (TM.getOptLevel() != CodeGenOpt::None) {
+ // Order cases by weight so the most likely case will be checked first.
+ std::sort(W.FirstCluster, W.LastCluster + 1,
+ [](const CaseCluster &a, const CaseCluster &b) {
+ return a.Weight > b.Weight;
+ });
+
+ // Rearrange the case blocks so that the last one falls through if possible.
+ // Start at the bottom as that's the case with the lowest weight.
+ // FIXME: Take branch probability into account.
+ for (CaseClusterIt I = W.LastCluster; I > W.FirstCluster; ) {
+ --I;
+ if (I->Kind == CC_Range && I->MBB == NextMBB) {
+ std::swap(*I, *W.LastCluster);
+ break;
+ }
+ }
+ }
+
+ // Compute total weight.
+ uint32_t UnhandledWeights = 0;
+ for (CaseClusterIt I = W.FirstCluster; I <= W.LastCluster; ++I)
+ UnhandledWeights += I->Weight;
+
+ MachineBasicBlock *CurMBB = W.MBB;
+ for (CaseClusterIt I = W.FirstCluster, E = W.LastCluster; I <= E; ++I) {
+ MachineBasicBlock *Fallthrough;
+ if (I == W.LastCluster) {
+ // For the last cluster, fall through to the default destination.
+ Fallthrough = DefaultMBB;
+ } else {
+ Fallthrough = CurMF->CreateMachineBasicBlock(CurMBB->getBasicBlock());
+ CurMF->insert(BBI, Fallthrough);
+ // Put Cond in a virtual register to make it available from the new blocks.
+ ExportFromCurrentBlock(Cond);
+ }
+
+ switch (I->Kind) {
+ case CC_JumpTable: {
+ // FIXME: Optimize away range check based on pivot comparisons.
+ JumpTableHeader *JTH = &JTCases[I->JTCasesIndex].first;
+ JumpTable *JT = &JTCases[I->JTCasesIndex].second;
+
+ // The jump block hasn't been inserted yet; insert it here.
+ MachineBasicBlock *JumpMBB = JT->MBB;
+ CurMF->insert(BBI, JumpMBB);
+ addSuccessorWithWeight(CurMBB, Fallthrough);
+ addSuccessorWithWeight(CurMBB, JumpMBB);
+
+ // The jump table header will be inserted in our current block, do the
+ // range check, and fall through to our fallthrough block.
+ JTH->HeaderBB = CurMBB;
+ JT->Default = Fallthrough; // FIXME: Move Default to JumpTableHeader.
+
+ // If we're in the right place, emit the jump table header right now.
+ if (CurMBB == SwitchMBB) {
+ visitJumpTableHeader(*JT, *JTH, SwitchMBB);
+ JTH->Emitted = true;
+ }
+ break;
+ }
+ case CC_BitTests: {
+ // FIXME: Optimize away range check based on pivot comparisons.
+ BitTestBlock *BTB = &BitTestCases[I->BTCasesIndex];
+
+ // The bit test blocks haven't been inserted yet; insert them here.
+ for (BitTestCase &BTC : BTB->Cases)
+ CurMF->insert(BBI, BTC.ThisBB);
+
+ // Fill in fields of the BitTestBlock.
+ BTB->Parent = CurMBB;
+ BTB->Default = Fallthrough;
+
+ // If we're in the right place, emit the bit test header header right now.
+ if (CurMBB ==SwitchMBB) {
+ visitBitTestHeader(*BTB, SwitchMBB);
+ BTB->Emitted = true;
+ }
+ break;
+ }
+ case CC_Range: {
+ const Value *RHS, *LHS, *MHS;
+ ISD::CondCode CC;
+ if (I->Low == I->High) {
+ // Check Cond == I->Low.
+ CC = ISD::SETEQ;
+ LHS = Cond;
+ RHS=I->Low;
+ MHS = nullptr;
+ } else {
+ // Check I->Low <= Cond <= I->High.
+ CC = ISD::SETLE;
+ LHS = I->Low;
+ MHS = Cond;
+ RHS = I->High;
+ }
+
+ // The false weight is the sum of all unhandled cases.
+ UnhandledWeights -= I->Weight;
+ CaseBlock CB(CC, LHS, RHS, MHS, I->MBB, Fallthrough, CurMBB, I->Weight,
+ UnhandledWeights);
+
+ if (CurMBB == SwitchMBB)
+ visitSwitchCase(CB, SwitchMBB);
+ else
+ SwitchCases.push_back(CB);
+
+ break;
+ }
+ }
+ CurMBB = Fallthrough;
+ }
+}
+
+void SelectionDAGBuilder::splitWorkItem(SwitchWorkList &WorkList,
+ const SwitchWorkListItem &W,
+ Value *Cond,
+ MachineBasicBlock *SwitchMBB) {
+ assert(W.FirstCluster->Low->getValue().slt(W.LastCluster->Low->getValue()) &&
+ "Clusters not sorted?");
+
+ unsigned NumClusters = W.LastCluster - W.FirstCluster + 1;
+ assert(NumClusters >= 2 && "Too small to split!");
+
+ // FIXME: When we have profile info, we might want to balance the tree based
+ // on weights instead of node count.
+
+ CaseClusterIt PivotCluster = W.FirstCluster + NumClusters / 2;
+ CaseClusterIt FirstLeft = W.FirstCluster;
+ CaseClusterIt LastLeft = PivotCluster - 1;
+ CaseClusterIt FirstRight = PivotCluster;
+ CaseClusterIt LastRight = W.LastCluster;
+ const ConstantInt *Pivot = PivotCluster->Low;
+
+ // New blocks will be inserted immediately after the current one.
+ MachineFunction::iterator BBI = W.MBB;
+ ++BBI;
+
+ // We will branch to the LHS if Value < Pivot. If LHS is a single cluster,
+ // we can branch to its destination directly if it's squeezed exactly in
+ // between the known lower bound and Pivot - 1.
+ MachineBasicBlock *LeftMBB;
+ if (FirstLeft == LastLeft && FirstLeft->Kind == CC_Range &&
+ FirstLeft->Low == W.GE &&
+ (FirstLeft->High->getValue() + 1LL) == Pivot->getValue()) {
+ LeftMBB = FirstLeft->MBB;
+ } else {
+ LeftMBB = FuncInfo.MF->CreateMachineBasicBlock(W.MBB->getBasicBlock());
+ FuncInfo.MF->insert(BBI, LeftMBB);
+ WorkList.push_back({LeftMBB, FirstLeft, LastLeft, W.GE, Pivot});
+ // Put Cond in a virtual register to make it available from the new blocks.
+ ExportFromCurrentBlock(Cond);
+ }
+
+ // Similarly, we will branch to the RHS if Value >= Pivot. If RHS is a
+ // single cluster, RHS.Low == Pivot, and we can branch to its destination
+ // directly if RHS.High equals the current upper bound.
+ MachineBasicBlock *RightMBB;
+ if (FirstRight == LastRight && FirstRight->Kind == CC_Range &&
+ W.LT && (FirstRight->High->getValue() + 1ULL) == W.LT->getValue()) {
+ RightMBB = FirstRight->MBB;
+ } else {
+ RightMBB = FuncInfo.MF->CreateMachineBasicBlock(W.MBB->getBasicBlock());
+ FuncInfo.MF->insert(BBI, RightMBB);
+ WorkList.push_back({RightMBB, FirstRight, LastRight, Pivot, W.LT});
+ // Put Cond in a virtual register to make it available from the new blocks.
+ ExportFromCurrentBlock(Cond);
+ }
+
+ // Create the CaseBlock record that will be used to lower the branch.
+ CaseBlock CB(ISD::SETLT, Cond, Pivot, nullptr, LeftMBB, RightMBB, W.MBB);
+
+ if (W.MBB == SwitchMBB)
+ visitSwitchCase(CB, SwitchMBB);
+ else
+ SwitchCases.push_back(CB);
+}
+
+void SelectionDAGBuilder::visitSwitch(const SwitchInst &SI) {
+ // Extract cases from the switch.
+ BranchProbabilityInfo *BPI = FuncInfo.BPI;
+ CaseClusterVector Clusters;
+ Clusters.reserve(SI.getNumCases());
+ for (auto I : SI.cases()) {
+ MachineBasicBlock *Succ = FuncInfo.MBBMap[I.getCaseSuccessor()];
+ const ConstantInt *CaseVal = I.getCaseValue();
+ uint32_t Weight = 0; // FIXME: Use 1 instead?
+ if (BPI)
+ Weight = BPI->getEdgeWeight(SI.getParent(), I.getSuccessorIndex());
+ Clusters.push_back(CaseCluster::range(CaseVal, CaseVal, Succ, Weight));
+ }
+
+ MachineBasicBlock *DefaultMBB = FuncInfo.MBBMap[SI.getDefaultDest()];
+
+ if (TM.getOptLevel() != CodeGenOpt::None) {
+ // Cluster adjacent cases with the same destination.
+ sortAndRangeify(Clusters);
+
+ // Replace an unreachable default with the most popular destination.
+ // FIXME: Exploit unreachable default more aggressively.
+ bool UnreachableDefault =
+ isa<UnreachableInst>(SI.getDefaultDest()->getFirstNonPHIOrDbg());
+ if (UnreachableDefault && !Clusters.empty()) {
+ DenseMap<const BasicBlock *, unsigned> Popularity;
+ unsigned MaxPop = 0;
+ const BasicBlock *MaxBB = nullptr;
+ for (auto I : SI.cases()) {
+ const BasicBlock *BB = I.getCaseSuccessor();
+ if (++Popularity[BB] > MaxPop) {
+ MaxPop = Popularity[BB];
+ MaxBB = BB;
+ }
+ }
+ // Set new default.
+ assert(MaxPop > 0 && MaxBB);
+ DefaultMBB = FuncInfo.MBBMap[MaxBB];
+
+ // Remove cases that were pointing to the destination that is now the
+ // default.
+ CaseClusterVector New;
+ New.reserve(Clusters.size());
+ for (CaseCluster &CC : Clusters) {
+ if (CC.MBB != DefaultMBB)
+ New.push_back(CC);
+ }
+ Clusters = std::move(New);
+ }
+ }
+
+ // If there is only the default destination, jump there directly.
+ MachineBasicBlock *SwitchMBB = FuncInfo.MBB;
+ if (Clusters.empty()) {
+ SwitchMBB->addSuccessor(DefaultMBB);
+ if (DefaultMBB != NextBlock(SwitchMBB)) {
+ DAG.setRoot(DAG.getNode(ISD::BR, getCurSDLoc(), MVT::Other,
+ getControlRoot(), DAG.getBasicBlock(DefaultMBB)));
+ }
+ return;
+ }
+
+ if (TM.getOptLevel() != CodeGenOpt::None) {
+ findJumpTables(Clusters, &SI, DefaultMBB);
+ findBitTestClusters(Clusters, &SI);
+ }
+
+
+ DEBUG({
+ dbgs() << "Case clusters: ";
+ for (const CaseCluster &C : Clusters) {
+ if (C.Kind == CC_JumpTable) dbgs() << "JT:";
+ if (C.Kind == CC_BitTests) dbgs() << "BT:";
+
+ C.Low->getValue().print(dbgs(), true);
+ if (C.Low != C.High) {
+ dbgs() << '-';
+ C.High->getValue().print(dbgs(), true);
+ }
+ dbgs() << ' ';
+ }
+ dbgs() << '\n';
+ });
+
+ assert(!Clusters.empty());
+ SwitchWorkList WorkList;
+ CaseClusterIt First = Clusters.begin();
+ CaseClusterIt Last = Clusters.end() - 1;
+ WorkList.push_back({SwitchMBB, First, Last, nullptr, nullptr});
+
+ while (!WorkList.empty()) {
+ SwitchWorkListItem W = WorkList.back();
+ WorkList.pop_back();
+ unsigned NumClusters = W.LastCluster - W.FirstCluster + 1;
+
+ if (NumClusters > 3 && TM.getOptLevel() != CodeGenOpt::None) {
+ // For optimized builds, lower large range as a balanced binary tree.
+ splitWorkItem(WorkList, W, SI.getCondition(), SwitchMBB);
+ continue;
+ }
+
+ lowerWorkItem(W, SI.getCondition(), SwitchMBB, DefaultMBB);
+ }
+}
projects / oota-llvm.git / commitdiff