TargetSubtargetInfo.h

Go to the documentation of this file.

//===- llvm/CodeGen/TargetSubtargetInfo.h - Target Information --*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file describes the subtarget options of a Target machine.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_TARGETSUBTARGETINFO_H
#define LLVM_CODEGEN_TARGETSUBTARGETINFO_H
 
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringTable.h"
#include "llvm/CodeGen/MacroFusion.h"
#include "llvm/CodeGen/PBQPRAConstraint.h"
#include "llvm/CodeGen/SchedulerRegistry.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/Compiler.h"
#include <memory>
#include <vector>
 
namespace llvm {
 
class APInt;
class BitVector;
class MachineFunction;
class ScheduleDAGMutation;
class CallLowering;
class GlobalValue;
class InlineAsmLowering;
class InstrItineraryData;
struct InstrStage;
class InstructionSelector;
class LegalizerInfo;
class LibcallLoweringInfo;
class MachineInstr;
struct MachineSchedPolicy;
struct MCReadAdvanceEntry;
struct MCSchedModel;
struct MCWriteLatencyEntry;
struct MCWriteProcResEntry;
class RegisterBankInfo;
class SDep;
class SelectionDAGTargetInfo;
class SUnit;
class TargetFrameLowering;
class TargetInstrInfo;
class TargetLowering;
class MCRegisterClass;
using TargetRegisterClass = MCRegisterClass;
class TargetRegisterInfo;
class TargetSchedModel;
class Triple;
struct SchedRegion;
 
//===----------------------------------------------------------------------===//
///
/// TargetSubtargetInfo - Generic base class for all target subtargets.  All
/// Target-specific options that control code generation and printing should
/// be exposed through a TargetSubtargetInfo-derived class.
///
class LLVM_ABI TargetSubtargetInfo : public MCSubtargetInfo {
protected: // Can only create subclasses...
  TargetSubtargetInfo(const Triple &TT, StringRef CPU, StringRef TuneCPU,
                      StringRef FS, StringTable PN,
                      ArrayRef<SubtargetFeatureKV> PF,
                      ArrayRef<SubtargetSubTypeKV> PD,
                      ArrayRef<SubtargetSubTypeAliasKV> PA,
                      const MCSchedModel *PSM, const MCWriteProcResEntry *WPR,
                      const MCWriteLatencyEntry *WL,
                      const MCReadAdvanceEntry *RA, const InstrStage *IS,
                      const unsigned *OC, const unsigned *FP);
 
public:
  // AntiDepBreakMode - Type of anti-dependence breaking that should
  // be performed before post-RA scheduling.
  using AntiDepBreakMode = enum { ANTIDEP_NONE, ANTIDEP_CRITICAL, ANTIDEP_ALL };
  using RegClassVector = SmallVectorImpl<const TargetRegisterClass *>;
 
  TargetSubtargetInfo() = delete;
  TargetSubtargetInfo(const TargetSubtargetInfo &) = delete;
  TargetSubtargetInfo &operator=(const TargetSubtargetInfo &) = delete;
  ~TargetSubtargetInfo() override;
 
  virtual bool isXRaySupported() const { return false; }
 
  /// \returns true if the target intrinsic \p IntrinsicID is supported by this
  /// subtarget.
  bool isIntrinsicSupported(unsigned IntrinsicID) const;
 
  // Interfaces to the major aspects of target machine information:
  //
  // -- Instruction opcode and operand information
  // -- Pipelines and scheduling information
  // -- Stack frame information
  // -- Selection DAG lowering information
  // -- Call lowering information
  //
  // N.B. These objects may change during compilation. It's not safe to cache
  // them between functions.
  virtual const TargetInstrInfo *getInstrInfo() const { return nullptr; }
  virtual const TargetFrameLowering *getFrameLowering() const {
    return nullptr;
  }
  virtual const TargetLowering *getTargetLowering() const { return nullptr; }
  virtual const SelectionDAGTargetInfo *getSelectionDAGInfo() const {
    return nullptr;
  }
  virtual const CallLowering *getCallLowering() const { return nullptr; }
 
  virtual const InlineAsmLowering *getInlineAsmLowering() const {
    return nullptr;
  }
 
  // FIXME: This lets targets specialize the selector by subtarget (which lets
  // us do things like a dedicated avx512 selector).  However, we might want
  // to also specialize selectors by MachineFunction, which would let us be
  // aware of optsize/optnone and such.
  virtual InstructionSelector *getInstructionSelector() const {
    return nullptr;
  }
 
  /// Target can subclass this hook to select a different DAG scheduler.
  virtual RegisterScheduler::FunctionPassCtor
  getDAGScheduler(CodeGenOptLevel) const {
    return nullptr;
  }
 
  virtual const LegalizerInfo *getLegalizerInfo() const { return nullptr; }
 
  /// Return the target's register information.
  virtual const TargetRegisterInfo *getRegisterInfo() const = 0;
 
  /// If the information for the register banks is available, return it.
  /// Otherwise return nullptr.
  virtual const RegisterBankInfo *getRegBankInfo() const { return nullptr; }
 
  /// getInstrItineraryData - Returns instruction itinerary data for the target
  /// or specific subtarget.
  virtual const InstrItineraryData *getInstrItineraryData() const {
    return nullptr;
  }
 
  /// Return the number of extra cycles the processor takes to recover from a
  /// branch misprediction. Defaults to the value in the scheduling model.
  virtual unsigned getMispredictionPenalty() const {
    return getSchedModel().MispredictPenalty;
  }
 
  /// Return the expected latency of load instructions. Defaults to the value
  /// in the scheduling model.
  virtual unsigned getLoadLatency() const {
    return getSchedModel().LoadLatency;
  }
 
  /// Configure the LibcallLoweringInfo for this subtarget. The libcalls will be
  /// pre-configured with defaults based on RuntimeLibcallsInfo. This may be
  /// used to override those decisions, such as disambiguating alternative
  /// implementations.
  virtual void initLibcallLoweringInfo(LibcallLoweringInfo &Info) const {}
 
  /// Resolve a SchedClass at runtime, where SchedClass identifies an
  /// MCSchedClassDesc with the isVariant property. This may return the ID of
  /// another variant SchedClass, but repeated invocation must quickly terminate
  /// in a nonvariant SchedClass.
  virtual unsigned resolveSchedClass(unsigned SchedClass,
                                     const MachineInstr *MI,
                                     const TargetSchedModel *SchedModel) const {
    return 0;
  }
 
  /// Returns true if MI is a dependency breaking zero-idiom instruction for the
  /// subtarget.
  ///
  /// This function also sets bits in Mask related to input operands that
  /// are not in a data dependency relationship.  There is one bit for each
  /// machine operand; implicit operands follow explicit operands in the bit
  /// representation used for Mask.  An empty (i.e. a mask with all bits
  /// cleared) means: data dependencies are "broken" for all the explicit input
  /// machine operands of MI.
  virtual bool isZeroIdiom(const MachineInstr *MI, APInt &Mask) const {
    return false;
  }
 
  /// Returns true if MI is a dependency breaking instruction for the subtarget.
  ///
  /// Similar in behavior to `isZeroIdiom`. However, it knows how to identify
  /// all dependency breaking instructions (i.e. not just zero-idioms).
  ///
  /// As for `isZeroIdiom`, this method returns a mask of "broken" dependencies.
  /// (See method `isZeroIdiom` for a detailed description of Mask).
  virtual bool isDependencyBreaking(const MachineInstr *MI, APInt &Mask) const {
    return isZeroIdiom(MI, Mask);
  }
 
  /// Returns true if MI is a candidate for move elimination.
  ///
  /// A candidate for move elimination may be optimized out at register renaming
  /// stage. Subtargets can specify the set of optimizable moves by
  /// instantiating tablegen class `IsOptimizableRegisterMove` (see
  /// llvm/Target/TargetInstrPredicate.td).
  ///
  /// SubtargetEmitter is responsible for processing all the definitions of class
  /// IsOptimizableRegisterMove, and auto-generate an override for this method.
  virtual bool isOptimizableRegisterMove(const MachineInstr *MI) const {
    return false;
  }
 
  /// True if the subtarget should run MachineScheduler after aggressive
  /// coalescing.
  ///
  /// This currently replaces the SelectionDAG scheduler with the "source" order
  /// scheduler (though see below for an option to turn this off and use the
  /// TargetLowering preference). It does not yet disable the postRA scheduler.
  virtual bool enableMachineScheduler() const;
 
  /// True if the machine scheduler should disable the TLI preference
  /// for preRA scheduling with the source level scheduler.
  virtual bool enableMachineSchedDefaultSched() const { return true; }
 
  /// True if the subtarget should run MachinePipeliner
  virtual bool enableMachinePipeliner() const { return true; };
 
  /// True if the subtarget should run WindowScheduler.
  virtual bool enableWindowScheduler() const { return true; }
 
  /// True if the subtarget should enable joining global copies.
  ///
  /// By default this is enabled if the machine scheduler is enabled, but
  /// can be overridden.
  virtual bool enableJoinGlobalCopies() const;
 
  /// Hack to bring up option. This should be unconditionally true, all targets
  /// should enable it and delete this.
  virtual bool enableTerminalRule() const { return false; }
 
  /// True if the subtarget should run a scheduler after register allocation.
  ///
  /// By default this queries the PostRAScheduling bit in the scheduling model
  /// which is the preferred way to influence this.
  virtual bool enablePostRAScheduler() const;
 
  /// True if the subtarget should run a machine scheduler after register
  /// allocation.
  virtual bool enablePostRAMachineScheduler() const;
 
  /// True if the subtarget should run the atomic expansion pass.
  virtual bool enableAtomicExpand() const;
 
  /// True if the subtarget should run the indirectbr expansion pass.
  virtual bool enableIndirectBrExpand() const;
 
  /// Override generic scheduling policy within a region.
  ///
  /// This is a convenient way for targets that don't provide any custom
  /// scheduling heuristics (no custom MachineSchedStrategy) to make
  /// changes to the generic scheduling policy.
  virtual void overrideSchedPolicy(MachineSchedPolicy &Policy,
                                   const SchedRegion &Region) const {}
 
  /// Override generic post-ra scheduling policy within a region.
  ///
  /// This is a convenient way for targets that don't provide any custom
  /// scheduling heuristics (no custom MachineSchedStrategy) to make
  /// changes to the generic  post-ra scheduling policy.
  /// Note that some options like tracking register pressure won't take effect
  /// in post-ra scheduling.
  virtual void overridePostRASchedPolicy(MachineSchedPolicy &Policy,
                                         const SchedRegion &Region) const {}
 
  // Perform target-specific adjustments to the latency of a schedule
  // dependency.
  // If a pair of operands is associated with the schedule dependency, DefOpIdx
  // and UseOpIdx are the indices of the operands in Def and Use, respectively.
  // Otherwise, either may be -1.
  virtual void adjustSchedDependency(SUnit *Def, int DefOpIdx, SUnit *Use,
                                     int UseOpIdx, SDep &Dep,
                                     const TargetSchedModel *SchedModel) const {
  }
 
  // For use with PostRAScheduling: get the anti-dependence breaking that should
  // be performed before post-RA scheduling.
  virtual AntiDepBreakMode getAntiDepBreakMode() const { return ANTIDEP_NONE; }
 
  // For use with PostRAScheduling: in CriticalPathRCs, return any register
  // classes that should only be considered for anti-dependence breaking if they
  // are on the critical path.
  virtual void getCriticalPathRCs(RegClassVector &CriticalPathRCs) const {
    return CriticalPathRCs.clear();
  }
 
  // Provide an ordered list of schedule DAG mutations for the post-RA
  // scheduler.
  virtual void getPostRAMutations(
      std::vector<std::unique_ptr<ScheduleDAGMutation>> &Mutations) const {
  }
 
  // Provide an ordered list of schedule DAG mutations for the machine
  // pipeliner.
  virtual void getSMSMutations(
      std::vector<std::unique_ptr<ScheduleDAGMutation>> &Mutations) const {
  }
 
  /// Default to DFA for resource management, return false when target will use
  /// ProcResource in InstrSchedModel instead.
  virtual bool useDFAforSMS() const { return true; }
 
  // For use with PostRAScheduling: get the minimum optimization level needed
  // to enable post-RA scheduling.
  virtual CodeGenOptLevel getOptLevelToEnablePostRAScheduler() const {
    return CodeGenOptLevel::Default;
  }
 
  /// True if the subtarget should run the local reassignment
  /// heuristic of the register allocator.
  /// This heuristic may be compile time intensive, \p OptLevel provides
  /// a finer grain to tune the register allocator.
  virtual bool enableRALocalReassignment(CodeGenOptLevel OptLevel) const;
 
  /// Enable use of alias analysis during code generation (during MI
  /// scheduling, DAGCombine, etc.).
  virtual bool useAA() const;
 
  /// \brief Sink addresses into blocks using GEP instructions rather than
  /// pointer casts and arithmetic.
  virtual bool addrSinkUsingGEPs() const {
    return useAA();
  }
 
  /// Enable the use of the early if conversion pass.
  virtual bool enableEarlyIfConversion() const { return false; }
 
  /// Return PBQPConstraint(s) for the target.
  ///
  /// Override to provide custom PBQP constraints.
  virtual std::unique_ptr<PBQPRAConstraint> getCustomPBQPConstraints() const {
    return nullptr;
  }
 
  /// Enable tracking of subregister liveness in register allocator.
  /// Please use MachineRegisterInfo::subRegLivenessEnabled() instead where
  /// possible.
  virtual bool enableSubRegLiveness() const { return false; }
 
  /// This is called after a .mir file was loaded.
  virtual void mirFileLoaded(MachineFunction &MF) const;
 
  /// Constructs a Mask of physical registers whose allocation orders should be
  /// used exactly as written in the TableGen descriptions, rather than
  /// allocating them later if they are callee-saved. Mask is empty on entry
  /// and must either remain empty or cover all physical registers.
  virtual void getCSRAllocationOrderMask(const MachineFunction &MF,
                                         BitVector &Mask) const {}
 
  /// Classify a global function reference. This mainly used to fetch target
  /// special flags for lowering a function address. For example mark a function
  /// call should be plt or pc-related addressing.
  virtual unsigned char
  classifyGlobalFunctionReference(const GlobalValue *GV) const {
    return 0;
  }
 
  /// Enable spillage copy elimination in MachineCopyPropagation pass. This
  /// helps removing redundant copies generated by register allocator when
  /// handling complex eviction chains.
  virtual bool enableSpillageCopyElimination() const { return false; }
 
  /// Get the list of MacroFusion predicates.
  virtual std::vector<MacroFusionPredTy> getMacroFusions() const { return {}; };
 
  /// Whether the target has instructions where an early-clobber result
  /// operand cannot overlap with an undef input operand.
  virtual bool requiresDisjointEarlyClobberAndUndef() const {
    // Conservatively assume such instructions exist by default.
    return true;
  }
 
  virtual bool isRegisterReservedByUser(Register R) const { return false; }
 
  /// Target features to ignore for inline compatibility check.
  virtual const FeatureBitset &getInlineIgnoreFeatures() const = 0;
  /// Target features where the callee may have an additional feature,
  /// instead of the caller.
  virtual const FeatureBitset &getInlineInverseFeatures() const = 0;
  /// Target features where all mismatches prevent inlining.
  virtual const FeatureBitset &getInlineMustMatchFeatures() const = 0;
 
private:
  /// Lazy, incrementally-populated cache for isIntrinsicSupported().
  mutable DenseMap<unsigned, bool> IntrinsicSupportCache;
};
} // end namespace llvm
 
#endif // LLVM_CODEGEN_TARGETSUBTARGETINFO_H