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//===- llvm/CodeGen/TargetSubtargetInfo.h - Target Information --*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file describes the subtarget options of a Target machine.
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/CodeGen/PBQPRAConstraint.h"
#include "llvm/CodeGen/ScheduleDAGMutation.h"
#include "llvm/CodeGen/SchedulerRegistry.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/Support/CodeGen.h"
#include <memory>
#include <vector>
namespace llvm {
class CallLowering;
class InstrItineraryData;
struct InstrStage;
class InstructionSelector;
class LegalizerInfo;
class MachineInstr;
struct MachineSchedPolicy;
struct MCReadAdvanceEntry;
struct MCWriteLatencyEntry;
struct MCWriteProcResEntry;
class RegisterBankInfo;
class SDep;
class SelectionDAGTargetInfo;
struct SubtargetFeatureKV;
struct SubtargetSubTypeKV;
struct SubtargetInfoKV;
class SUnit;
class TargetFrameLowering;
class TargetInstrInfo;
class TargetLowering;
class TargetRegisterClass;
class TargetRegisterInfo;
class TargetSchedModel;
class Triple;
/// 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 TargetSubtargetInfo : public MCSubtargetInfo {
protected: // Can only create subclasses...
TargetSubtargetInfo(const Triple &TT, StringRef CPU, StringRef FS,
ArrayRef<SubtargetFeatureKV> PF,
ArrayRef<SubtargetSubTypeKV> PD,
const MCWriteProcResEntry *WPR,
const MCWriteLatencyEntry *WL,
const MCReadAdvanceEntry *RA, const InstrStage *IS,
const unsigned *OC, const unsigned *FP);
// AntiDepBreakMode - Type of anti-dependence breaking that should
// be performed before post-RA scheduling.
using RegClassVector = SmallVectorImpl<const TargetRegisterClass *>;
TargetSubtargetInfo() = delete;
TargetSubtargetInfo(const TargetSubtargetInfo &) = delete;
TargetSubtargetInfo &operator=(const TargetSubtargetInfo &) = delete;
~TargetSubtargetInfo() override;
virtual bool isXRaySupported() const { return false; }
// 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; }
// 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 const InstructionSelector *getInstructionSelector() const {
return nullptr;
virtual unsigned getHwMode() const { return 0; }
/// Target can subclass this hook to select a different DAG scheduler.
virtual RegisterScheduler::FunctionPassCtor
getDAGScheduler(CodeGenOpt::Level) const {
return nullptr;
virtual const LegalizerInfo *getLegalizerInfo() const { return nullptr; }
/// getRegisterInfo - If register information is available, return it. If
/// not, return null.
virtual const TargetRegisterInfo *getRegisterInfo() const { return nullptr; }
/// 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;
/// 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/
/// 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 enable joining global copies.
/// By default this is enabled if the machine scheduler is enabled, but
/// can be overridden.
virtual bool enableJoinGlobalCopies() const;
/// 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 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,
unsigned NumRegionInstrs) const {}
// Perform target specific adjustments to the latency of a schedule
// dependency.
virtual void adjustSchedDependency(SUnit *def, SUnit *use, SDep &dep) 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 {
// For use with PostRAScheduling: get the minimum optimization level needed
// to enable post-RA scheduling.
virtual CodeGenOpt::Level getOptLevelToEnablePostRAScheduler() const {
return CodeGenOpt::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(CodeGenOpt::Level OptLevel) const;
/// True if the subtarget should consider the cost of local intervals
/// created by a split candidate when choosing the best split candidate. This
/// heuristic may be compile time intensive.
virtual bool enableAdvancedRASplitCost() const;
/// Enable use of alias analysis during code generation (during MI
/// scheduling, DAGCombine, etc.).
virtual bool useAA() const;
/// 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;
} // end namespace llvm