//===-- SelectionDAGISel.cpp - Implement the SelectionDAGISel class -------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This implements the SelectionDAGISel class. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "isel" #include "ScheduleDAGSDNodes.h" #include "SelectionDAGBuild.h" #include "llvm/CodeGen/SelectionDAGISel.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Constants.h" #include "llvm/CallingConv.h" #include "llvm/DerivedTypes.h" #include "llvm/Function.h" #include "llvm/GlobalVariable.h" #include "llvm/InlineAsm.h" #include "llvm/Instructions.h" #include "llvm/Intrinsics.h" #include "llvm/IntrinsicInst.h" #include "llvm/CodeGen/FastISel.h" #include "llvm/CodeGen/GCStrategy.h" #include "llvm/CodeGen/GCMetadata.h" #include "llvm/CodeGen/MachineFunction.h" #include "llvm/CodeGen/MachineFrameInfo.h" #include "llvm/CodeGen/MachineInstrBuilder.h" #include "llvm/CodeGen/MachineJumpTableInfo.h" #include "llvm/CodeGen/MachineModuleInfo.h" #include "llvm/CodeGen/MachineRegisterInfo.h" #include "llvm/CodeGen/ScheduleHazardRecognizer.h" #include "llvm/CodeGen/SchedulerRegistry.h" #include "llvm/CodeGen/SelectionDAG.h" #include "llvm/CodeGen/DwarfWriter.h" #include "llvm/Target/TargetRegisterInfo.h" #include "llvm/Target/TargetData.h" #include "llvm/Target/TargetFrameInfo.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetLowering.h" #include "llvm/Target/TargetMachine.h" #include "llvm/Target/TargetOptions.h" #include "llvm/Support/Compiler.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/Timer.h" #include using namespace llvm; static cl::opt DisableLegalizeTypes("disable-legalize-types", cl::Hidden); static cl::opt EnableFastISelVerbose("fast-isel-verbose", cl::Hidden, cl::desc("Enable verbose messages in the \"fast\" " "instruction selector")); static cl::opt EnableFastISelAbort("fast-isel-abort", cl::Hidden, cl::desc("Enable abort calls when \"fast\" instruction fails")); static cl::opt SchedLiveInCopies("schedule-livein-copies", cl::desc("Schedule copies of livein registers"), cl::init(false)); #ifndef NDEBUG static cl::opt ViewDAGCombine1("view-dag-combine1-dags", cl::Hidden, cl::desc("Pop up a window to show dags before the first " "dag combine pass")); static cl::opt ViewLegalizeTypesDAGs("view-legalize-types-dags", cl::Hidden, cl::desc("Pop up a window to show dags before legalize types")); static cl::opt ViewLegalizeDAGs("view-legalize-dags", cl::Hidden, cl::desc("Pop up a window to show dags before legalize")); static cl::opt ViewDAGCombine2("view-dag-combine2-dags", cl::Hidden, cl::desc("Pop up a window to show dags before the second " "dag combine pass")); static cl::opt ViewDAGCombineLT("view-dag-combine-lt-dags", cl::Hidden, cl::desc("Pop up a window to show dags before the post legalize types" " dag combine pass")); static cl::opt ViewISelDAGs("view-isel-dags", cl::Hidden, cl::desc("Pop up a window to show isel dags as they are selected")); static cl::opt ViewSchedDAGs("view-sched-dags", cl::Hidden, cl::desc("Pop up a window to show sched dags as they are processed")); static cl::opt ViewSUnitDAGs("view-sunit-dags", cl::Hidden, cl::desc("Pop up a window to show SUnit dags after they are processed")); #else static const bool ViewDAGCombine1 = false, ViewLegalizeTypesDAGs = false, ViewLegalizeDAGs = false, ViewDAGCombine2 = false, ViewDAGCombineLT = false, ViewISelDAGs = false, ViewSchedDAGs = false, ViewSUnitDAGs = false; #endif //===---------------------------------------------------------------------===// /// /// RegisterScheduler class - Track the registration of instruction schedulers. /// //===---------------------------------------------------------------------===// MachinePassRegistry RegisterScheduler::Registry; //===---------------------------------------------------------------------===// /// /// ISHeuristic command line option for instruction schedulers. /// //===---------------------------------------------------------------------===// static cl::opt > ISHeuristic("pre-RA-sched", cl::init(&createDefaultScheduler), cl::desc("Instruction schedulers available (before register" " allocation):")); static RegisterScheduler defaultListDAGScheduler("default", "Best scheduler for the target", createDefaultScheduler); namespace llvm { //===--------------------------------------------------------------------===// /// createDefaultScheduler - This creates an instruction scheduler appropriate /// for the target. ScheduleDAGSDNodes* createDefaultScheduler(SelectionDAGISel *IS, CodeGenOpt::Level OptLevel) { const TargetLowering &TLI = IS->getTargetLowering(); if (OptLevel == CodeGenOpt::None) return createFastDAGScheduler(IS, OptLevel); if (TLI.getSchedulingPreference() == TargetLowering::SchedulingForLatency) return createTDListDAGScheduler(IS, OptLevel); assert(TLI.getSchedulingPreference() == TargetLowering::SchedulingForRegPressure && "Unknown sched type!"); return createBURRListDAGScheduler(IS, OptLevel); } } // EmitInstrWithCustomInserter - This method should be implemented by targets // that mark instructions with the 'usesCustomDAGSchedInserter' flag. These // instructions are special in various ways, which require special support to // insert. The specified MachineInstr is created but not inserted into any // basic blocks, and the scheduler passes ownership of it to this method. MachineBasicBlock *TargetLowering::EmitInstrWithCustomInserter(MachineInstr *MI, MachineBasicBlock *MBB) const { llvm_report_error("If a target marks an instruction with " "'usesCustomDAGSchedInserter', it must implement " "TargetLowering::EmitInstrWithCustomInserter!"); return 0; } /// EmitLiveInCopy - Emit a copy for a live in physical register. If the /// physical register has only a single copy use, then coalesced the copy /// if possible. static void EmitLiveInCopy(MachineBasicBlock *MBB, MachineBasicBlock::iterator &InsertPos, unsigned VirtReg, unsigned PhysReg, const TargetRegisterClass *RC, DenseMap &CopyRegMap, const MachineRegisterInfo &MRI, const TargetRegisterInfo &TRI, const TargetInstrInfo &TII) { unsigned NumUses = 0; MachineInstr *UseMI = NULL; for (MachineRegisterInfo::use_iterator UI = MRI.use_begin(VirtReg), UE = MRI.use_end(); UI != UE; ++UI) { UseMI = &*UI; if (++NumUses > 1) break; } // If the number of uses is not one, or the use is not a move instruction, // don't coalesce. Also, only coalesce away a virtual register to virtual // register copy. bool Coalesced = false; unsigned SrcReg, DstReg, SrcSubReg, DstSubReg; if (NumUses == 1 && TII.isMoveInstr(*UseMI, SrcReg, DstReg, SrcSubReg, DstSubReg) && TargetRegisterInfo::isVirtualRegister(DstReg)) { VirtReg = DstReg; Coalesced = true; } // Now find an ideal location to insert the copy. MachineBasicBlock::iterator Pos = InsertPos; while (Pos != MBB->begin()) { MachineInstr *PrevMI = prior(Pos); DenseMap::iterator RI = CopyRegMap.find(PrevMI); // copyRegToReg might emit multiple instructions to do a copy. unsigned CopyDstReg = (RI == CopyRegMap.end()) ? 0 : RI->second; if (CopyDstReg && !TRI.regsOverlap(CopyDstReg, PhysReg)) // This is what the BB looks like right now: // r1024 = mov r0 // ... // r1 = mov r1024 // // We want to insert "r1025 = mov r1". Inserting this copy below the // move to r1024 makes it impossible for that move to be coalesced. // // r1025 = mov r1 // r1024 = mov r0 // ... // r1 = mov 1024 // r2 = mov 1025 break; // Woot! Found a good location. --Pos; } bool Emitted = TII.copyRegToReg(*MBB, Pos, VirtReg, PhysReg, RC, RC); assert(Emitted && "Unable to issue a live-in copy instruction!\n"); (void) Emitted; CopyRegMap.insert(std::make_pair(prior(Pos), VirtReg)); if (Coalesced) { if (&*InsertPos == UseMI) ++InsertPos; MBB->erase(UseMI); } } /// EmitLiveInCopies - If this is the first basic block in the function, /// and if it has live ins that need to be copied into vregs, emit the /// copies into the block. static void EmitLiveInCopies(MachineBasicBlock *EntryMBB, const MachineRegisterInfo &MRI, const TargetRegisterInfo &TRI, const TargetInstrInfo &TII) { if (SchedLiveInCopies) { // Emit the copies at a heuristically-determined location in the block. DenseMap CopyRegMap; MachineBasicBlock::iterator InsertPos = EntryMBB->begin(); for (MachineRegisterInfo::livein_iterator LI = MRI.livein_begin(), E = MRI.livein_end(); LI != E; ++LI) if (LI->second) { const TargetRegisterClass *RC = MRI.getRegClass(LI->second); EmitLiveInCopy(EntryMBB, InsertPos, LI->second, LI->first, RC, CopyRegMap, MRI, TRI, TII); } } else { // Emit the copies into the top of the block. for (MachineRegisterInfo::livein_iterator LI = MRI.livein_begin(), E = MRI.livein_end(); LI != E; ++LI) if (LI->second) { const TargetRegisterClass *RC = MRI.getRegClass(LI->second); bool Emitted = TII.copyRegToReg(*EntryMBB, EntryMBB->begin(), LI->second, LI->first, RC, RC); assert(Emitted && "Unable to issue a live-in copy instruction!\n"); (void) Emitted; } } } //===----------------------------------------------------------------------===// // SelectionDAGISel code //===----------------------------------------------------------------------===// SelectionDAGISel::SelectionDAGISel(TargetMachine &tm, CodeGenOpt::Level OL) : FunctionPass(&ID), TM(tm), TLI(*tm.getTargetLowering()), FuncInfo(new FunctionLoweringInfo(TLI)), CurDAG(new SelectionDAG(TLI, *FuncInfo)), SDL(new SelectionDAGLowering(*CurDAG, TLI, *FuncInfo, OL)), GFI(), OptLevel(OL), DAGSize(0) {} SelectionDAGISel::~SelectionDAGISel() { delete SDL; delete CurDAG; delete FuncInfo; } unsigned SelectionDAGISel::MakeReg(MVT VT) { return RegInfo->createVirtualRegister(TLI.getRegClassFor(VT)); } void SelectionDAGISel::getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequired(); AU.addRequired(); AU.addRequired(); AU.setPreservesAll(); } bool SelectionDAGISel::runOnFunction(Function &Fn) { // Do some sanity-checking on the command-line options. assert((!EnableFastISelVerbose || EnableFastISel) && "-fast-isel-verbose requires -fast-isel"); assert((!EnableFastISelAbort || EnableFastISel) && "-fast-isel-abort requires -fast-isel"); // Do not codegen any 'available_externally' functions at all, they have // definitions outside the translation unit. if (Fn.hasAvailableExternallyLinkage()) return false; // Get alias analysis for load/store combining. AA = &getAnalysis(); TargetMachine &TM = TLI.getTargetMachine(); MF = &MachineFunction::construct(&Fn, TM); const TargetInstrInfo &TII = *TM.getInstrInfo(); const TargetRegisterInfo &TRI = *TM.getRegisterInfo(); if (MF->getFunction()->hasGC()) GFI = &getAnalysis().getFunctionInfo(*MF->getFunction()); else GFI = 0; RegInfo = &MF->getRegInfo(); DOUT << "\n\n\n=== " << Fn.getName() << "\n"; MachineModuleInfo *MMI = getAnalysisIfAvailable(); DwarfWriter *DW = getAnalysisIfAvailable(); CurDAG->init(*MF, MMI, DW); FuncInfo->set(Fn, *MF, *CurDAG, EnableFastISel); SDL->init(GFI, *AA); for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) if (InvokeInst *Invoke = dyn_cast(I->getTerminator())) // Mark landing pad. FuncInfo->MBBMap[Invoke->getSuccessor(1)]->setIsLandingPad(); SelectAllBasicBlocks(Fn, *MF, MMI, DW, TII); // If the first basic block in the function has live ins that need to be // copied into vregs, emit the copies into the top of the block before // emitting the code for the block. EmitLiveInCopies(MF->begin(), *RegInfo, TRI, TII); // Add function live-ins to entry block live-in set. for (MachineRegisterInfo::livein_iterator I = RegInfo->livein_begin(), E = RegInfo->livein_end(); I != E; ++I) MF->begin()->addLiveIn(I->first); #ifndef NDEBUG assert(FuncInfo->CatchInfoFound.size() == FuncInfo->CatchInfoLost.size() && "Not all catch info was assigned to a landing pad!"); #endif FuncInfo->clear(); return true; } static void copyCatchInfo(BasicBlock *SrcBB, BasicBlock *DestBB, MachineModuleInfo *MMI, FunctionLoweringInfo &FLI) { for (BasicBlock::iterator I = SrcBB->begin(), E = --SrcBB->end(); I != E; ++I) if (EHSelectorInst *EHSel = dyn_cast(I)) { // Apply the catch info to DestBB. AddCatchInfo(*EHSel, MMI, FLI.MBBMap[DestBB]); #ifndef NDEBUG if (!FLI.MBBMap[SrcBB]->isLandingPad()) FLI.CatchInfoFound.insert(EHSel); #endif } } /// IsFixedFrameObjectWithPosOffset - Check if object is a fixed frame object and /// whether object offset >= 0. static bool IsFixedFrameObjectWithPosOffset(MachineFrameInfo *MFI, SDValue Op) { if (!isa(Op)) return false; FrameIndexSDNode * FrameIdxNode = dyn_cast(Op); int FrameIdx = FrameIdxNode->getIndex(); return MFI->isFixedObjectIndex(FrameIdx) && MFI->getObjectOffset(FrameIdx) >= 0; } /// IsPossiblyOverwrittenArgumentOfTailCall - Check if the operand could /// possibly be overwritten when lowering the outgoing arguments in a tail /// call. Currently the implementation of this call is very conservative and /// assumes all arguments sourcing from FORMAL_ARGUMENTS or a CopyFromReg with /// virtual registers would be overwritten by direct lowering. static bool IsPossiblyOverwrittenArgumentOfTailCall(SDValue Op, MachineFrameInfo *MFI) { RegisterSDNode * OpReg = NULL; if (Op.getOpcode() == ISD::FORMAL_ARGUMENTS || (Op.getOpcode()== ISD::CopyFromReg && (OpReg = dyn_cast(Op.getOperand(1))) && (OpReg->getReg() >= TargetRegisterInfo::FirstVirtualRegister)) || (Op.getOpcode() == ISD::LOAD && IsFixedFrameObjectWithPosOffset(MFI, Op.getOperand(1))) || (Op.getOpcode() == ISD::MERGE_VALUES && Op.getOperand(Op.getResNo()).getOpcode() == ISD::LOAD && IsFixedFrameObjectWithPosOffset(MFI, Op.getOperand(Op.getResNo()). getOperand(1)))) return true; return false; } /// CheckDAGForTailCallsAndFixThem - This Function looks for CALL nodes in the /// DAG and fixes their tailcall attribute operand. static void CheckDAGForTailCallsAndFixThem(SelectionDAG &DAG, const TargetLowering& TLI) { SDNode * Ret = NULL; SDValue Terminator = DAG.getRoot(); // Find RET node. if (Terminator.getOpcode() == ISD::RET) { Ret = Terminator.getNode(); } // Fix tail call attribute of CALL nodes. for (SelectionDAG::allnodes_iterator BE = DAG.allnodes_begin(), BI = DAG.allnodes_end(); BI != BE; ) { --BI; if (CallSDNode *TheCall = dyn_cast(BI)) { SDValue OpRet(Ret, 0); SDValue OpCall(BI, 0); bool isMarkedTailCall = TheCall->isTailCall(); // If CALL node has tail call attribute set to true and the call is not // eligible (no RET or the target rejects) the attribute is fixed to // false. The TargetLowering::IsEligibleForTailCallOptimization function // must correctly identify tail call optimizable calls. if (!isMarkedTailCall) continue; if (Ret==NULL || !TLI.IsEligibleForTailCallOptimization(TheCall, OpRet, DAG)) { // Not eligible. Mark CALL node as non tail call. Note that we // can modify the call node in place since calls are not CSE'd. TheCall->setNotTailCall(); } else { // Look for tail call clobbered arguments. Emit a series of // copyto/copyfrom virtual register nodes to protect them. SmallVector Ops; SDValue Chain = TheCall->getChain(), InFlag; Ops.push_back(Chain); Ops.push_back(TheCall->getCallee()); for (unsigned i = 0, e = TheCall->getNumArgs(); i != e; ++i) { SDValue Arg = TheCall->getArg(i); bool isByVal = TheCall->getArgFlags(i).isByVal(); MachineFunction &MF = DAG.getMachineFunction(); MachineFrameInfo *MFI = MF.getFrameInfo(); if (!isByVal && IsPossiblyOverwrittenArgumentOfTailCall(Arg, MFI)) { MVT VT = Arg.getValueType(); unsigned VReg = MF.getRegInfo(). createVirtualRegister(TLI.getRegClassFor(VT)); Chain = DAG.getCopyToReg(Chain, Arg.getDebugLoc(), VReg, Arg, InFlag); InFlag = Chain.getValue(1); Arg = DAG.getCopyFromReg(Chain, Arg.getDebugLoc(), VReg, VT, InFlag); Chain = Arg.getValue(1); InFlag = Arg.getValue(2); } Ops.push_back(Arg); Ops.push_back(TheCall->getArgFlagsVal(i)); } // Link in chain of CopyTo/CopyFromReg. Ops[0] = Chain; DAG.UpdateNodeOperands(OpCall, Ops.begin(), Ops.size()); } } } } void SelectionDAGISel::SelectBasicBlock(BasicBlock *LLVMBB, BasicBlock::iterator Begin, BasicBlock::iterator End) { SDL->setCurrentBasicBlock(BB); // Lower all of the non-terminator instructions. for (BasicBlock::iterator I = Begin; I != End; ++I) if (!isa(I)) SDL->visit(*I); // Ensure that all instructions which are used outside of their defining // blocks are available as virtual registers. Invoke is handled elsewhere. for (BasicBlock::iterator I = Begin; I != End; ++I) if (!isa(I) && !isa(I)) SDL->CopyToExportRegsIfNeeded(I); // Handle PHI nodes in successor blocks. if (End == LLVMBB->end()) { HandlePHINodesInSuccessorBlocks(LLVMBB); // Lower the terminator after the copies are emitted. SDL->visit(*LLVMBB->getTerminator()); } // Make sure the root of the DAG is up-to-date. CurDAG->setRoot(SDL->getControlRoot()); // Check whether calls in this block are real tail calls. Fix up CALL nodes // with correct tailcall attribute so that the target can rely on the tailcall // attribute indicating whether the call is really eligible for tail call // optimization. if (PerformTailCallOpt) CheckDAGForTailCallsAndFixThem(*CurDAG, TLI); // Final step, emit the lowered DAG as machine code. CodeGenAndEmitDAG(); SDL->clear(); } void SelectionDAGISel::ComputeLiveOutVRegInfo() { SmallPtrSet VisitedNodes; SmallVector Worklist; Worklist.push_back(CurDAG->getRoot().getNode()); APInt Mask; APInt KnownZero; APInt KnownOne; while (!Worklist.empty()) { SDNode *N = Worklist.back(); Worklist.pop_back(); // If we've already seen this node, ignore it. if (!VisitedNodes.insert(N)) continue; // Otherwise, add all chain operands to the worklist. for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) if (N->getOperand(i).getValueType() == MVT::Other) Worklist.push_back(N->getOperand(i).getNode()); // If this is a CopyToReg with a vreg dest, process it. if (N->getOpcode() != ISD::CopyToReg) continue; unsigned DestReg = cast(N->getOperand(1))->getReg(); if (!TargetRegisterInfo::isVirtualRegister(DestReg)) continue; // Ignore non-scalar or non-integer values. SDValue Src = N->getOperand(2); MVT SrcVT = Src.getValueType(); if (!SrcVT.isInteger() || SrcVT.isVector()) continue; unsigned NumSignBits = CurDAG->ComputeNumSignBits(Src); Mask = APInt::getAllOnesValue(SrcVT.getSizeInBits()); CurDAG->ComputeMaskedBits(Src, Mask, KnownZero, KnownOne); // Only install this information if it tells us something. if (NumSignBits != 1 || KnownZero != 0 || KnownOne != 0) { DestReg -= TargetRegisterInfo::FirstVirtualRegister; FunctionLoweringInfo &FLI = CurDAG->getFunctionLoweringInfo(); if (DestReg >= FLI.LiveOutRegInfo.size()) FLI.LiveOutRegInfo.resize(DestReg+1); FunctionLoweringInfo::LiveOutInfo &LOI = FLI.LiveOutRegInfo[DestReg]; LOI.NumSignBits = NumSignBits; LOI.KnownOne = KnownOne; LOI.KnownZero = KnownZero; } } } void SelectionDAGISel::CodeGenAndEmitDAG() { std::string GroupName; if (TimePassesIsEnabled) GroupName = "Instruction Selection and Scheduling"; std::string BlockName; if (ViewDAGCombine1 || ViewLegalizeTypesDAGs || ViewLegalizeDAGs || ViewDAGCombine2 || ViewDAGCombineLT || ViewISelDAGs || ViewSchedDAGs || ViewSUnitDAGs) BlockName = CurDAG->getMachineFunction().getFunction()->getName() + ':' + BB->getBasicBlock()->getName(); DOUT << "Initial selection DAG:\n"; DEBUG(CurDAG->dump()); if (ViewDAGCombine1) CurDAG->viewGraph("dag-combine1 input for " + BlockName); // Run the DAG combiner in pre-legalize mode. if (TimePassesIsEnabled) { NamedRegionTimer T("DAG Combining 1", GroupName); CurDAG->Combine(Unrestricted, *AA, OptLevel); } else { CurDAG->Combine(Unrestricted, *AA, OptLevel); } DOUT << "Optimized lowered selection DAG:\n"; DEBUG(CurDAG->dump()); // Second step, hack on the DAG until it only uses operations and types that // the target supports. if (!DisableLegalizeTypes) { if (ViewLegalizeTypesDAGs) CurDAG->viewGraph("legalize-types input for " + BlockName); bool Changed; if (TimePassesIsEnabled) { NamedRegionTimer T("Type Legalization", GroupName); Changed = CurDAG->LegalizeTypes(); } else { Changed = CurDAG->LegalizeTypes(); } DOUT << "Type-legalized selection DAG:\n"; DEBUG(CurDAG->dump()); if (Changed) { if (ViewDAGCombineLT) CurDAG->viewGraph("dag-combine-lt input for " + BlockName); // Run the DAG combiner in post-type-legalize mode. if (TimePassesIsEnabled) { NamedRegionTimer T("DAG Combining after legalize types", GroupName); CurDAG->Combine(NoIllegalTypes, *AA, OptLevel); } else { CurDAG->Combine(NoIllegalTypes, *AA, OptLevel); } DOUT << "Optimized type-legalized selection DAG:\n"; DEBUG(CurDAG->dump()); } if (TimePassesIsEnabled) { NamedRegionTimer T("Vector Legalization", GroupName); Changed = CurDAG->LegalizeVectors(); } else { Changed = CurDAG->LegalizeVectors(); } if (Changed) { if (TimePassesIsEnabled) { NamedRegionTimer T("Type Legalization 2", GroupName); Changed = CurDAG->LegalizeTypes(); } else { Changed = CurDAG->LegalizeTypes(); } if (ViewDAGCombineLT) CurDAG->viewGraph("dag-combine-lv input for " + BlockName); // Run the DAG combiner in post-type-legalize mode. if (TimePassesIsEnabled) { NamedRegionTimer T("DAG Combining after legalize vectors", GroupName); CurDAG->Combine(NoIllegalOperations, *AA, OptLevel); } else { CurDAG->Combine(NoIllegalOperations, *AA, OptLevel); } DOUT << "Optimized vector-legalized selection DAG:\n"; DEBUG(CurDAG->dump()); } } if (ViewLegalizeDAGs) CurDAG->viewGraph("legalize input for " + BlockName); if (TimePassesIsEnabled) { NamedRegionTimer T("DAG Legalization", GroupName); CurDAG->Legalize(DisableLegalizeTypes, OptLevel); } else { CurDAG->Legalize(DisableLegalizeTypes, OptLevel); } DOUT << "Legalized selection DAG:\n"; DEBUG(CurDAG->dump()); if (ViewDAGCombine2) CurDAG->viewGraph("dag-combine2 input for " + BlockName); // Run the DAG combiner in post-legalize mode. if (TimePassesIsEnabled) { NamedRegionTimer T("DAG Combining 2", GroupName); CurDAG->Combine(NoIllegalOperations, *AA, OptLevel); } else { CurDAG->Combine(NoIllegalOperations, *AA, OptLevel); } DOUT << "Optimized legalized selection DAG:\n"; DEBUG(CurDAG->dump()); if (ViewISelDAGs) CurDAG->viewGraph("isel input for " + BlockName); if (OptLevel != CodeGenOpt::None) ComputeLiveOutVRegInfo(); // Third, instruction select all of the operations to machine code, adding the // code to the MachineBasicBlock. if (TimePassesIsEnabled) { NamedRegionTimer T("Instruction Selection", GroupName); InstructionSelect(); } else { InstructionSelect(); } DOUT << "Selected selection DAG:\n"; DEBUG(CurDAG->dump()); if (ViewSchedDAGs) CurDAG->viewGraph("scheduler input for " + BlockName); // Schedule machine code. ScheduleDAGSDNodes *Scheduler = CreateScheduler(); if (TimePassesIsEnabled) { NamedRegionTimer T("Instruction Scheduling", GroupName); Scheduler->Run(CurDAG, BB, BB->end()); } else { Scheduler->Run(CurDAG, BB, BB->end()); } if (ViewSUnitDAGs) Scheduler->viewGraph(); // Emit machine code to BB. This can change 'BB' to the last block being // inserted into. if (TimePassesIsEnabled) { NamedRegionTimer T("Instruction Creation", GroupName); BB = Scheduler->EmitSchedule(); } else { BB = Scheduler->EmitSchedule(); } // Free the scheduler state. if (TimePassesIsEnabled) { NamedRegionTimer T("Instruction Scheduling Cleanup", GroupName); delete Scheduler; } else { delete Scheduler; } DOUT << "Selected machine code:\n"; DEBUG(BB->dump()); } void SelectionDAGISel::SelectAllBasicBlocks(Function &Fn, MachineFunction &MF, MachineModuleInfo *MMI, DwarfWriter *DW, const TargetInstrInfo &TII) { // Initialize the Fast-ISel state, if needed. FastISel *FastIS = 0; if (EnableFastISel) FastIS = TLI.createFastISel(MF, MMI, DW, FuncInfo->ValueMap, FuncInfo->MBBMap, FuncInfo->StaticAllocaMap #ifndef NDEBUG , FuncInfo->CatchInfoLost #endif ); // Iterate over all basic blocks in the function. for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { BasicBlock *LLVMBB = &*I; BB = FuncInfo->MBBMap[LLVMBB]; BasicBlock::iterator const Begin = LLVMBB->begin(); BasicBlock::iterator const End = LLVMBB->end(); BasicBlock::iterator BI = Begin; // Lower any arguments needed in this block if this is the entry block. bool SuppressFastISel = false; if (LLVMBB == &Fn.getEntryBlock()) { LowerArguments(LLVMBB); // If any of the arguments has the byval attribute, forgo // fast-isel in the entry block. if (FastIS) { unsigned j = 1; for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(); I != E; ++I, ++j) if (Fn.paramHasAttr(j, Attribute::ByVal)) { if (EnableFastISelVerbose || EnableFastISelAbort) cerr << "FastISel skips entry block due to byval argument\n"; SuppressFastISel = true; break; } } } if (MMI && BB->isLandingPad()) { // Add a label to mark the beginning of the landing pad. Deletion of the // landing pad can thus be detected via the MachineModuleInfo. unsigned LabelID = MMI->addLandingPad(BB); const TargetInstrDesc &II = TII.get(TargetInstrInfo::EH_LABEL); BuildMI(BB, SDL->getCurDebugLoc(), II).addImm(LabelID); // Mark exception register as live in. unsigned Reg = TLI.getExceptionAddressRegister(); if (Reg) BB->addLiveIn(Reg); // Mark exception selector register as live in. Reg = TLI.getExceptionSelectorRegister(); if (Reg) BB->addLiveIn(Reg); // FIXME: Hack around an exception handling flaw (PR1508): the personality // function and list of typeids logically belong to the invoke (or, if you // like, the basic block containing the invoke), and need to be associated // with it in the dwarf exception handling tables. Currently however the // information is provided by an intrinsic (eh.selector) that can be moved // to unexpected places by the optimizers: if the unwind edge is critical, // then breaking it can result in the intrinsics being in the successor of // the landing pad, not the landing pad itself. This results in exceptions // not being caught because no typeids are associated with the invoke. // This may not be the only way things can go wrong, but it is the only way // we try to work around for the moment. BranchInst *Br = dyn_cast(LLVMBB->getTerminator()); if (Br && Br->isUnconditional()) { // Critical edge? BasicBlock::iterator I, E; for (I = LLVMBB->begin(), E = --LLVMBB->end(); I != E; ++I) if (isa(I)) break; if (I == E) // No catch info found - try to extract some from the successor. copyCatchInfo(Br->getSuccessor(0), LLVMBB, MMI, *FuncInfo); } } // Before doing SelectionDAG ISel, see if FastISel has been requested. if (FastIS && !SuppressFastISel) { // Emit code for any incoming arguments. This must happen before // beginning FastISel on the entry block. if (LLVMBB == &Fn.getEntryBlock()) { CurDAG->setRoot(SDL->getControlRoot()); CodeGenAndEmitDAG(); SDL->clear(); } FastIS->startNewBlock(BB); // Do FastISel on as many instructions as possible. for (; BI != End; ++BI) { // Just before the terminator instruction, insert instructions to // feed PHI nodes in successor blocks. if (isa(BI)) if (!HandlePHINodesInSuccessorBlocksFast(LLVMBB, FastIS)) { if (EnableFastISelVerbose || EnableFastISelAbort) { cerr << "FastISel miss: "; BI->dump(); } if (EnableFastISelAbort) LLVM_UNREACHABLE("FastISel didn't handle a PHI in a successor"); break; } // First try normal tablegen-generated "fast" selection. if (FastIS->SelectInstruction(BI)) continue; // Next, try calling the target to attempt to handle the instruction. if (FastIS->TargetSelectInstruction(BI)) continue; // Then handle certain instructions as single-LLVM-Instruction blocks. if (isa(BI)) { if (EnableFastISelVerbose || EnableFastISelAbort) { cerr << "FastISel missed call: "; BI->dump(); } if (BI->getType() != Type::VoidTy) { unsigned &R = FuncInfo->ValueMap[BI]; if (!R) R = FuncInfo->CreateRegForValue(BI); } SDL->setCurDebugLoc(FastIS->getCurDebugLoc()); SelectBasicBlock(LLVMBB, BI, next(BI)); // If the instruction was codegen'd with multiple blocks, // inform the FastISel object where to resume inserting. FastIS->setCurrentBlock(BB); continue; } // Otherwise, give up on FastISel for the rest of the block. // For now, be a little lenient about non-branch terminators. if (!isa(BI) || isa(BI)) { if (EnableFastISelVerbose || EnableFastISelAbort) { cerr << "FastISel miss: "; BI->dump(); } if (EnableFastISelAbort) // The "fast" selector couldn't handle something and bailed. // For the purpose of debugging, just abort. LLVM_UNREACHABLE("FastISel didn't select the entire block"); } break; } } // Run SelectionDAG instruction selection on the remainder of the block // not handled by FastISel. If FastISel is not run, this is the entire // block. if (BI != End) { // If FastISel is run and it has known DebugLoc then use it. if (FastIS && !FastIS->getCurDebugLoc().isUnknown()) SDL->setCurDebugLoc(FastIS->getCurDebugLoc()); SelectBasicBlock(LLVMBB, BI, End); } FinishBasicBlock(); } delete FastIS; } void SelectionDAGISel::FinishBasicBlock() { DOUT << "Target-post-processed machine code:\n"; DEBUG(BB->dump()); DOUT << "Total amount of phi nodes to update: " << SDL->PHINodesToUpdate.size() << "\n"; DEBUG(for (unsigned i = 0, e = SDL->PHINodesToUpdate.size(); i != e; ++i) DOUT << "Node " << i << " : (" << SDL->PHINodesToUpdate[i].first << ", " << SDL->PHINodesToUpdate[i].second << ")\n";); // Next, now that we know what the last MBB the LLVM BB expanded is, update // PHI nodes in successors. if (SDL->SwitchCases.empty() && SDL->JTCases.empty() && SDL->BitTestCases.empty()) { for (unsigned i = 0, e = SDL->PHINodesToUpdate.size(); i != e; ++i) { MachineInstr *PHI = SDL->PHINodesToUpdate[i].first; assert(PHI->getOpcode() == TargetInstrInfo::PHI && "This is not a machine PHI node that we are updating!"); PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[i].second, false)); PHI->addOperand(MachineOperand::CreateMBB(BB)); } SDL->PHINodesToUpdate.clear(); return; } for (unsigned i = 0, e = SDL->BitTestCases.size(); i != e; ++i) { // Lower header first, if it wasn't already lowered if (!SDL->BitTestCases[i].Emitted) { // Set the current basic block to the mbb we wish to insert the code into BB = SDL->BitTestCases[i].Parent; SDL->setCurrentBasicBlock(BB); // Emit the code SDL->visitBitTestHeader(SDL->BitTestCases[i]); CurDAG->setRoot(SDL->getRoot()); CodeGenAndEmitDAG(); SDL->clear(); } for (unsigned j = 0, ej = SDL->BitTestCases[i].Cases.size(); j != ej; ++j) { // Set the current basic block to the mbb we wish to insert the code into BB = SDL->BitTestCases[i].Cases[j].ThisBB; SDL->setCurrentBasicBlock(BB); // Emit the code if (j+1 != ej) SDL->visitBitTestCase(SDL->BitTestCases[i].Cases[j+1].ThisBB, SDL->BitTestCases[i].Reg, SDL->BitTestCases[i].Cases[j]); else SDL->visitBitTestCase(SDL->BitTestCases[i].Default, SDL->BitTestCases[i].Reg, SDL->BitTestCases[i].Cases[j]); CurDAG->setRoot(SDL->getRoot()); CodeGenAndEmitDAG(); SDL->clear(); } // Update PHI Nodes for (unsigned pi = 0, pe = SDL->PHINodesToUpdate.size(); pi != pe; ++pi) { MachineInstr *PHI = SDL->PHINodesToUpdate[pi].first; MachineBasicBlock *PHIBB = PHI->getParent(); assert(PHI->getOpcode() == TargetInstrInfo::PHI && "This is not a machine PHI node that we are updating!"); // This is "default" BB. We have two jumps to it. From "header" BB and // from last "case" BB. if (PHIBB == SDL->BitTestCases[i].Default) { PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second, false)); PHI->addOperand(MachineOperand::CreateMBB(SDL->BitTestCases[i].Parent)); PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second, false)); PHI->addOperand(MachineOperand::CreateMBB(SDL->BitTestCases[i].Cases. back().ThisBB)); } // One of "cases" BB. for (unsigned j = 0, ej = SDL->BitTestCases[i].Cases.size(); j != ej; ++j) { MachineBasicBlock* cBB = SDL->BitTestCases[i].Cases[j].ThisBB; if (cBB->succ_end() != std::find(cBB->succ_begin(),cBB->succ_end(), PHIBB)) { PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second, false)); PHI->addOperand(MachineOperand::CreateMBB(cBB)); } } } } SDL->BitTestCases.clear(); // If the JumpTable record is filled in, then we need to emit a jump table. // Updating the PHI nodes is tricky in this case, since we need to determine // whether the PHI is a successor of the range check MBB or the jump table MBB for (unsigned i = 0, e = SDL->JTCases.size(); i != e; ++i) { // Lower header first, if it wasn't already lowered if (!SDL->JTCases[i].first.Emitted) { // Set the current basic block to the mbb we wish to insert the code into BB = SDL->JTCases[i].first.HeaderBB; SDL->setCurrentBasicBlock(BB); // Emit the code SDL->visitJumpTableHeader(SDL->JTCases[i].second, SDL->JTCases[i].first); CurDAG->setRoot(SDL->getRoot()); CodeGenAndEmitDAG(); SDL->clear(); } // Set the current basic block to the mbb we wish to insert the code into BB = SDL->JTCases[i].second.MBB; SDL->setCurrentBasicBlock(BB); // Emit the code SDL->visitJumpTable(SDL->JTCases[i].second); CurDAG->setRoot(SDL->getRoot()); CodeGenAndEmitDAG(); SDL->clear(); // Update PHI Nodes for (unsigned pi = 0, pe = SDL->PHINodesToUpdate.size(); pi != pe; ++pi) { MachineInstr *PHI = SDL->PHINodesToUpdate[pi].first; MachineBasicBlock *PHIBB = PHI->getParent(); assert(PHI->getOpcode() == TargetInstrInfo::PHI && "This is not a machine PHI node that we are updating!"); // "default" BB. We can go there only from header BB. if (PHIBB == SDL->JTCases[i].second.Default) { PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second, false)); PHI->addOperand(MachineOperand::CreateMBB(SDL->JTCases[i].first.HeaderBB)); } // JT BB. Just iterate over successors here if (BB->succ_end() != std::find(BB->succ_begin(),BB->succ_end(), PHIBB)) { PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pi].second, false)); PHI->addOperand(MachineOperand::CreateMBB(BB)); } } } SDL->JTCases.clear(); // If the switch block involved a branch to one of the actual successors, we // need to update PHI nodes in that block. for (unsigned i = 0, e = SDL->PHINodesToUpdate.size(); i != e; ++i) { MachineInstr *PHI = SDL->PHINodesToUpdate[i].first; assert(PHI->getOpcode() == TargetInstrInfo::PHI && "This is not a machine PHI node that we are updating!"); if (BB->isSuccessor(PHI->getParent())) { PHI->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[i].second, false)); PHI->addOperand(MachineOperand::CreateMBB(BB)); } } // If we generated any switch lowering information, build and codegen any // additional DAGs necessary. for (unsigned i = 0, e = SDL->SwitchCases.size(); i != e; ++i) { // Set the current basic block to the mbb we wish to insert the code into BB = SDL->SwitchCases[i].ThisBB; SDL->setCurrentBasicBlock(BB); // Emit the code SDL->visitSwitchCase(SDL->SwitchCases[i]); CurDAG->setRoot(SDL->getRoot()); CodeGenAndEmitDAG(); SDL->clear(); // Handle any PHI nodes in successors of this chunk, as if we were coming // from the original BB before switch expansion. Note that PHI nodes can // occur multiple times in PHINodesToUpdate. We have to be very careful to // handle them the right number of times. while ((BB = SDL->SwitchCases[i].TrueBB)) { // Handle LHS and RHS. for (MachineBasicBlock::iterator Phi = BB->begin(); Phi != BB->end() && Phi->getOpcode() == TargetInstrInfo::PHI; ++Phi){ // This value for this PHI node is recorded in PHINodesToUpdate, get it. for (unsigned pn = 0; ; ++pn) { assert(pn != SDL->PHINodesToUpdate.size() && "Didn't find PHI entry!"); if (SDL->PHINodesToUpdate[pn].first == Phi) { Phi->addOperand(MachineOperand::CreateReg(SDL->PHINodesToUpdate[pn]. second, false)); Phi->addOperand(MachineOperand::CreateMBB(SDL->SwitchCases[i].ThisBB)); break; } } } // Don't process RHS if same block as LHS. if (BB == SDL->SwitchCases[i].FalseBB) SDL->SwitchCases[i].FalseBB = 0; // If we haven't handled the RHS, do so now. Otherwise, we're done. SDL->SwitchCases[i].TrueBB = SDL->SwitchCases[i].FalseBB; SDL->SwitchCases[i].FalseBB = 0; } assert(SDL->SwitchCases[i].TrueBB == 0 && SDL->SwitchCases[i].FalseBB == 0); } SDL->SwitchCases.clear(); SDL->PHINodesToUpdate.clear(); } /// Create the scheduler. If a specific scheduler was specified /// via the SchedulerRegistry, use it, otherwise select the /// one preferred by the target. /// ScheduleDAGSDNodes *SelectionDAGISel::CreateScheduler() { RegisterScheduler::FunctionPassCtor Ctor = RegisterScheduler::getDefault(); if (!Ctor) { Ctor = ISHeuristic; RegisterScheduler::setDefault(Ctor); } return Ctor(this, OptLevel); } ScheduleHazardRecognizer *SelectionDAGISel::CreateTargetHazardRecognizer() { return new ScheduleHazardRecognizer(); } //===----------------------------------------------------------------------===// // Helper functions used by the generated instruction selector. //===----------------------------------------------------------------------===// // Calls to these methods are generated by tblgen. /// CheckAndMask - The isel is trying to match something like (and X, 255). If /// the dag combiner simplified the 255, we still want to match. RHS is the /// actual value in the DAG on the RHS of an AND, and DesiredMaskS is the value /// specified in the .td file (e.g. 255). bool SelectionDAGISel::CheckAndMask(SDValue LHS, ConstantSDNode *RHS, int64_t DesiredMaskS) const { const APInt &ActualMask = RHS->getAPIntValue(); const APInt &DesiredMask = APInt(LHS.getValueSizeInBits(), DesiredMaskS); // If the actual mask exactly matches, success! if (ActualMask == DesiredMask) return true; // If the actual AND mask is allowing unallowed bits, this doesn't match. if (ActualMask.intersects(~DesiredMask)) return false; // Otherwise, the DAG Combiner may have proven that the value coming in is // either already zero or is not demanded. Check for known zero input bits. APInt NeededMask = DesiredMask & ~ActualMask; if (CurDAG->MaskedValueIsZero(LHS, NeededMask)) return true; // TODO: check to see if missing bits are just not demanded. // Otherwise, this pattern doesn't match. return false; } /// CheckOrMask - The isel is trying to match something like (or X, 255). If /// the dag combiner simplified the 255, we still want to match. RHS is the /// actual value in the DAG on the RHS of an OR, and DesiredMaskS is the value /// specified in the .td file (e.g. 255). bool SelectionDAGISel::CheckOrMask(SDValue LHS, ConstantSDNode *RHS, int64_t DesiredMaskS) const { const APInt &ActualMask = RHS->getAPIntValue(); const APInt &DesiredMask = APInt(LHS.getValueSizeInBits(), DesiredMaskS); // If the actual mask exactly matches, success! if (ActualMask == DesiredMask) return true; // If the actual AND mask is allowing unallowed bits, this doesn't match. if (ActualMask.intersects(~DesiredMask)) return false; // Otherwise, the DAG Combiner may have proven that the value coming in is // either already zero or is not demanded. Check for known zero input bits. APInt NeededMask = DesiredMask & ~ActualMask; APInt KnownZero, KnownOne; CurDAG->ComputeMaskedBits(LHS, NeededMask, KnownZero, KnownOne); // If all the missing bits in the or are already known to be set, match! if ((NeededMask & KnownOne) == NeededMask) return true; // TODO: check to see if missing bits are just not demanded. // Otherwise, this pattern doesn't match. return false; } /// SelectInlineAsmMemoryOperands - Calls to this are automatically generated /// by tblgen. Others should not call it. void SelectionDAGISel:: SelectInlineAsmMemoryOperands(std::vector &Ops) { std::vector InOps; std::swap(InOps, Ops); Ops.push_back(InOps[0]); // input chain. Ops.push_back(InOps[1]); // input asm string. unsigned i = 2, e = InOps.size(); if (InOps[e-1].getValueType() == MVT::Flag) --e; // Don't process a flag operand if it is here. while (i != e) { unsigned Flags = cast(InOps[i])->getZExtValue(); if ((Flags & 7) != 4 /*MEM*/) { // Just skip over this operand, copying the operands verbatim. Ops.insert(Ops.end(), InOps.begin()+i, InOps.begin()+i+InlineAsm::getNumOperandRegisters(Flags) + 1); i += InlineAsm::getNumOperandRegisters(Flags) + 1; } else { assert(InlineAsm::getNumOperandRegisters(Flags) == 1 && "Memory operand with multiple values?"); // Otherwise, this is a memory operand. Ask the target to select it. std::vector SelOps; if (SelectInlineAsmMemoryOperand(InOps[i+1], 'm', SelOps)) { llvm_report_error("Could not match memory address. Inline asm" " failure!"); } // Add this to the output node. MVT IntPtrTy = CurDAG->getTargetLoweringInfo().getPointerTy(); Ops.push_back(CurDAG->getTargetConstant(4/*MEM*/ | (SelOps.size()<< 3), IntPtrTy)); Ops.insert(Ops.end(), SelOps.begin(), SelOps.end()); i += 2; } } // Add the flag input back if present. if (e != InOps.size()) Ops.push_back(InOps.back()); } /// findFlagUse - Return use of MVT::Flag value produced by the specified /// SDNode. /// static SDNode *findFlagUse(SDNode *N) { unsigned FlagResNo = N->getNumValues()-1; for (SDNode::use_iterator I = N->use_begin(), E = N->use_end(); I != E; ++I) { SDUse &Use = I.getUse(); if (Use.getResNo() == FlagResNo) return Use.getUser(); } return NULL; } /// findNonImmUse - Return true if "Use" is a non-immediate use of "Def". /// This function recursively traverses up the operand chain, ignoring /// certain nodes. static bool findNonImmUse(SDNode *Use, SDNode* Def, SDNode *ImmedUse, SDNode *Root, SmallPtrSet &Visited) { if (Use->getNodeId() < Def->getNodeId() || !Visited.insert(Use)) return false; for (unsigned i = 0, e = Use->getNumOperands(); i != e; ++i) { SDNode *N = Use->getOperand(i).getNode(); if (N == Def) { if (Use == ImmedUse || Use == Root) continue; // We are not looking for immediate use. assert(N != Root); return true; } // Traverse up the operand chain. if (findNonImmUse(N, Def, ImmedUse, Root, Visited)) return true; } return false; } /// isNonImmUse - Start searching from Root up the DAG to check is Def can /// be reached. Return true if that's the case. However, ignore direct uses /// by ImmedUse (which would be U in the example illustrated in /// IsLegalAndProfitableToFold) and by Root (which can happen in the store /// case). /// FIXME: to be really generic, we should allow direct use by any node /// that is being folded. But realisticly since we only fold loads which /// have one non-chain use, we only need to watch out for load/op/store /// and load/op/cmp case where the root (store / cmp) may reach the load via /// its chain operand. static inline bool isNonImmUse(SDNode *Root, SDNode *Def, SDNode *ImmedUse) { SmallPtrSet Visited; return findNonImmUse(Root, Def, ImmedUse, Root, Visited); } /// IsLegalAndProfitableToFold - Returns true if the specific operand node N of /// U can be folded during instruction selection that starts at Root and /// folding N is profitable. bool SelectionDAGISel::IsLegalAndProfitableToFold(SDNode *N, SDNode *U, SDNode *Root) const { if (OptLevel == CodeGenOpt::None) return false; // If Root use can somehow reach N through a path that that doesn't contain // U then folding N would create a cycle. e.g. In the following // diagram, Root can reach N through X. If N is folded into into Root, then // X is both a predecessor and a successor of U. // // [N*] // // ^ ^ // // / \ // // [U*] [X]? // // ^ ^ // // \ / // // \ / // // [Root*] // // // * indicates nodes to be folded together. // // If Root produces a flag, then it gets (even more) interesting. Since it // will be "glued" together with its flag use in the scheduler, we need to // check if it might reach N. // // [N*] // // ^ ^ // // / \ // // [U*] [X]? // // ^ ^ // // \ \ // // \ | // // [Root*] | // // ^ | // // f | // // | / // // [Y] / // // ^ / // // f / // // | / // // [FU] // // // If FU (flag use) indirectly reaches N (the load), and Root folds N // (call it Fold), then X is a predecessor of FU and a successor of // Fold. But since Fold and FU are flagged together, this will create // a cycle in the scheduling graph. MVT VT = Root->getValueType(Root->getNumValues()-1); while (VT == MVT::Flag) { SDNode *FU = findFlagUse(Root); if (FU == NULL) break; Root = FU; VT = Root->getValueType(Root->getNumValues()-1); } return !isNonImmUse(Root, N, U); } char SelectionDAGISel::ID = 0;