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//==- CodeGen/TargetRegisterInfo.h - Target Register 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 an abstract interface used to get information about a
// target machines register file. This information is used for a variety of
// purposed, especially register allocation.
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MachineValueType.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Printable.h"
#include <cassert>
#include <cstdint>
#include <functional>
namespace llvm {
class BitVector;
class LiveRegMatrix;
class MachineFunction;
class MachineInstr;
class RegScavenger;
class VirtRegMap;
class LiveIntervals;
class TargetRegisterClass {
using iterator = const MCPhysReg *;
using const_iterator = const MCPhysReg *;
using sc_iterator = const TargetRegisterClass* const *;
// Instance variables filled by tablegen, do not use!
const MCRegisterClass *MC;
const uint32_t *SubClassMask;
const uint16_t *SuperRegIndices;
const LaneBitmask LaneMask;
/// Classes with a higher priority value are assigned first by register
/// allocators using a greedy heuristic. The value is in the range [0,63].
const uint8_t AllocationPriority;
/// Whether the class supports two (or more) disjunct subregister indices.
const bool HasDisjunctSubRegs;
/// Whether a combination of subregisters can cover every register in the
/// class. See also the CoveredBySubRegs description in
const bool CoveredBySubRegs;
const sc_iterator SuperClasses;
ArrayRef<MCPhysReg> (*OrderFunc)(const MachineFunction&);
/// Return the register class ID number.
unsigned getID() const { return MC->getID(); }
/// begin/end - Return all of the registers in this class.
iterator begin() const { return MC->begin(); }
iterator end() const { return MC->end(); }
/// Return the number of registers in this class.
unsigned getNumRegs() const { return MC->getNumRegs(); }
getRegisters() const {
return make_range(MC->begin(), MC->end());
/// Return the specified register in the class.
unsigned getRegister(unsigned i) const {
return MC->getRegister(i);
/// Return true if the specified register is included in this register class.
/// This does not include virtual registers.
bool contains(unsigned Reg) const {
/// FIXME: Historically this function has returned false when given vregs
/// but it should probably only receive physical registers
if (!Register::isPhysicalRegister(Reg))
return false;
return MC->contains(Reg);
/// Return true if both registers are in this class.
bool contains(unsigned Reg1, unsigned Reg2) const {
/// FIXME: Historically this function has returned false when given a vregs
/// but it should probably only receive physical registers
if (!Register::isPhysicalRegister(Reg1) ||
return false;
return MC->contains(Reg1, Reg2);
/// Return the cost of copying a value between two registers in this class.
/// A negative number means the register class is very expensive
/// to copy e.g. status flag register classes.
int getCopyCost() const { return MC->getCopyCost(); }
/// Return true if this register class may be used to create virtual
/// registers.
bool isAllocatable() const { return MC->isAllocatable(); }
/// Return true if the specified TargetRegisterClass
/// is a proper sub-class of this TargetRegisterClass.
bool hasSubClass(const TargetRegisterClass *RC) const {
return RC != this && hasSubClassEq(RC);
/// Returns true if RC is a sub-class of or equal to this class.
bool hasSubClassEq(const TargetRegisterClass *RC) const {
unsigned ID = RC->getID();
return (SubClassMask[ID / 32] >> (ID % 32)) & 1;
/// Return true if the specified TargetRegisterClass is a
/// proper super-class of this TargetRegisterClass.
bool hasSuperClass(const TargetRegisterClass *RC) const {
return RC->hasSubClass(this);
/// Returns true if RC is a super-class of or equal to this class.
bool hasSuperClassEq(const TargetRegisterClass *RC) const {
return RC->hasSubClassEq(this);
/// Returns a bit vector of subclasses, including this one.
/// The vector is indexed by class IDs.
/// To use it, consider the returned array as a chunk of memory that
/// contains an array of bits of size NumRegClasses. Each 32-bit chunk
/// contains a bitset of the ID of the subclasses in big-endian style.
/// I.e., the representation of the memory from left to right at the
/// bit level looks like:
/// [31 30 ... 1 0] [ 63 62 ... 33 32] ...
/// [ XXX NumRegClasses NumRegClasses - 1 ... ]
/// Where the number represents the class ID and XXX bits that
/// should be ignored.
/// See the implementation of hasSubClassEq for an example of how it
/// can be used.
const uint32_t *getSubClassMask() const {
return SubClassMask;
/// Returns a 0-terminated list of sub-register indices that project some
/// super-register class into this register class. The list has an entry for
/// each Idx such that:
/// There exists SuperRC where:
/// For all Reg in SuperRC:
/// this->contains(Reg:Idx)
const uint16_t *getSuperRegIndices() const {
return SuperRegIndices;
/// Returns a NULL-terminated list of super-classes. The
/// classes are ordered by ID which is also a topological ordering from large
/// to small classes. The list does NOT include the current class.
sc_iterator getSuperClasses() const {
return SuperClasses;
/// Return true if this TargetRegisterClass is a subset
/// class of at least one other TargetRegisterClass.
bool isASubClass() const {
return SuperClasses[0] != nullptr;
/// Returns the preferred order for allocating registers from this register
/// class in MF. The raw order comes directly from the .td file and may
/// include reserved registers that are not allocatable.
/// Register allocators should also make sure to allocate
/// callee-saved registers only after all the volatiles are used. The
/// RegisterClassInfo class provides filtered allocation orders with
/// callee-saved registers moved to the end.
/// The MachineFunction argument can be used to tune the allocatable
/// registers based on the characteristics of the function, subtarget, or
/// other criteria.
/// By default, this method returns all registers in the class.
ArrayRef<MCPhysReg> getRawAllocationOrder(const MachineFunction &MF) const {
return OrderFunc ? OrderFunc(MF) : makeArrayRef(begin(), getNumRegs());
/// Returns the combination of all lane masks of register in this class.
/// The lane masks of the registers are the combination of all lane masks
/// of their subregisters. Returns 1 if there are no subregisters.
LaneBitmask getLaneMask() const {
return LaneMask;
/// Extra information, not in MCRegisterDesc, about registers.
/// These are used by codegen, not by MC.
struct TargetRegisterInfoDesc {
unsigned CostPerUse; // Extra cost of instructions using register.
bool inAllocatableClass; // Register belongs to an allocatable regclass.
/// Each TargetRegisterClass has a per register weight, and weight
/// limit which must be less than the limits of its pressure sets.
struct RegClassWeight {
unsigned RegWeight;
unsigned WeightLimit;
/// TargetRegisterInfo base class - We assume that the target defines a static
/// array of TargetRegisterDesc objects that represent all of the machine
/// registers that the target has. As such, we simply have to track a pointer
/// to this array so that we can turn register number into a register
/// descriptor.
class TargetRegisterInfo : public MCRegisterInfo {
using regclass_iterator = const TargetRegisterClass * const *;
using vt_iterator = const MVT::SimpleValueType *;
struct RegClassInfo {
unsigned RegSize, SpillSize, SpillAlignment;
vt_iterator VTList;
const TargetRegisterInfoDesc *InfoDesc; // Extra desc array for codegen
const char *const *SubRegIndexNames; // Names of subreg indexes.
// Pointer to array of lane masks, one per sub-reg index.
const LaneBitmask *SubRegIndexLaneMasks;
regclass_iterator RegClassBegin, RegClassEnd; // List of regclasses
LaneBitmask CoveringLanes;
const RegClassInfo *const RCInfos;
unsigned HwMode;
TargetRegisterInfo(const TargetRegisterInfoDesc *ID,
regclass_iterator RCB,
regclass_iterator RCE,
const char *const *SRINames,
const LaneBitmask *SRILaneMasks,
LaneBitmask CoveringLanes,
const RegClassInfo *const RCIs,
unsigned Mode = 0);
virtual ~TargetRegisterInfo();
// Register numbers can represent physical registers, virtual registers, and
// sometimes stack slots. The unsigned values are divided into these ranges:
// 0 Not a register, can be used as a sentinel.
// [1;2^30) Physical registers assigned by TableGen.
// [2^30;2^31) Stack slots. (Rarely used.)
// [2^31;2^32) Virtual registers assigned by MachineRegisterInfo.
// Further sentinels can be allocated from the small negative integers.
// DenseMapInfo<unsigned> uses -1u and -2u.
/// Return the size in bits of a register from class RC.
unsigned getRegSizeInBits(const TargetRegisterClass &RC) const {
return getRegClassInfo(RC).RegSize;
/// Return the size in bytes of the stack slot allocated to hold a spilled
/// copy of a register from class RC.
unsigned getSpillSize(const TargetRegisterClass &RC) const {
return getRegClassInfo(RC).SpillSize / 8;
/// Return the minimum required alignment in bytes for a spill slot for
/// a register of this class.
unsigned getSpillAlignment(const TargetRegisterClass &RC) const {
return getRegClassInfo(RC).SpillAlignment / 8;
/// Return true if the given TargetRegisterClass has the ValueType T.
bool isTypeLegalForClass(const TargetRegisterClass &RC, MVT T) const {
for (auto I = legalclasstypes_begin(RC); *I != MVT::Other; ++I)
if (MVT(*I) == T)
return true;
return false;
/// Loop over all of the value types that can be represented by values
/// in the given register class.
vt_iterator legalclasstypes_begin(const TargetRegisterClass &RC) const {
return getRegClassInfo(RC).VTList;
vt_iterator legalclasstypes_end(const TargetRegisterClass &RC) const {
vt_iterator I = legalclasstypes_begin(RC);
while (*I != MVT::Other)
return I;
/// Returns the Register Class of a physical register of the given type,
/// picking the most sub register class of the right type that contains this
/// physreg.
const TargetRegisterClass *
getMinimalPhysRegClass(unsigned Reg, MVT VT = MVT::Other) const;
/// Return the maximal subclass of the given register class that is
/// allocatable or NULL.
const TargetRegisterClass *
getAllocatableClass(const TargetRegisterClass *RC) const;
/// Returns a bitset indexed by register number indicating if a register is
/// allocatable or not. If a register class is specified, returns the subset
/// for the class.
BitVector getAllocatableSet(const MachineFunction &MF,
const TargetRegisterClass *RC = nullptr) const;
/// Return the additional cost of using this register instead
/// of other registers in its class.
unsigned getCostPerUse(unsigned RegNo) const {
return InfoDesc[RegNo].CostPerUse;
/// Return true if the register is in the allocation of any register class.
bool isInAllocatableClass(unsigned RegNo) const {
return InfoDesc[RegNo].inAllocatableClass;
/// Return the human-readable symbolic target-specific
/// name for the specified SubRegIndex.
const char *getSubRegIndexName(unsigned SubIdx) const {
assert(SubIdx && SubIdx < getNumSubRegIndices() &&
"This is not a subregister index");
return SubRegIndexNames[SubIdx-1];
/// Return a bitmask representing the parts of a register that are covered by
/// SubIdx \see LaneBitmask.
/// SubIdx == 0 is allowed, it has the lane mask ~0u.
LaneBitmask getSubRegIndexLaneMask(unsigned SubIdx) const {
assert(SubIdx < getNumSubRegIndices() && "This is not a subregister index");
return SubRegIndexLaneMasks[SubIdx];
/// The lane masks returned by getSubRegIndexLaneMask() above can only be
/// used to determine if sub-registers overlap - they can't be used to
/// determine if a set of sub-registers completely cover another
/// sub-register.
/// The X86 general purpose registers have two lanes corresponding to the
/// sub_8bit and sub_8bit_hi sub-registers. Both sub_32bit and sub_16bit have
/// lane masks '3', but the sub_16bit sub-register doesn't fully cover the
/// sub_32bit sub-register.
/// On the other hand, the ARM NEON lanes fully cover their registers: The
/// dsub_0 sub-register is completely covered by the ssub_0 and ssub_1 lanes.
/// This is related to the CoveredBySubRegs property on register definitions.
/// This function returns a bit mask of lanes that completely cover their
/// sub-registers. More precisely, given:
/// Covering = getCoveringLanes();
/// MaskA = getSubRegIndexLaneMask(SubA);
/// MaskB = getSubRegIndexLaneMask(SubB);
/// If (MaskA & ~(MaskB & Covering)) == 0, then SubA is completely covered by
/// SubB.
LaneBitmask getCoveringLanes() const { return CoveringLanes; }
/// Returns true if the two registers are equal or alias each other.
/// The registers may be virtual registers.
bool regsOverlap(Register regA, Register regB) const {
if (regA == regB) return true;
if (regA.isVirtual() || regB.isVirtual())
return false;
// Regunits are numerically ordered. Find a common unit.
MCRegUnitIterator RUA(regA, this);
MCRegUnitIterator RUB(regB, this);
do {
if (*RUA == *RUB) return true;
if (*RUA < *RUB) ++RUA;
else ++RUB;
} while (RUA.isValid() && RUB.isValid());
return false;
/// Returns true if Reg contains RegUnit.
bool hasRegUnit(unsigned Reg, unsigned RegUnit) const {
for (MCRegUnitIterator Units(Reg, this); Units.isValid(); ++Units)
if (*Units == RegUnit)
return true;
return false;
/// Returns the original SrcReg unless it is the target of a copy-like
/// operation, in which case we chain backwards through all such operations
/// to the ultimate source register. If a physical register is encountered,
/// we stop the search.
virtual unsigned lookThruCopyLike(unsigned SrcReg,
const MachineRegisterInfo *MRI) const;
/// Return a null-terminated list of all of the callee-saved registers on
/// this target. The register should be in the order of desired callee-save
/// stack frame offset. The first register is closest to the incoming stack
/// pointer if stack grows down, and vice versa.
/// Notice: This function does not take into account disabled CSRs.
/// In most cases you will want to use instead the function
/// getCalleeSavedRegs that is implemented in MachineRegisterInfo.
virtual const MCPhysReg*
getCalleeSavedRegs(const MachineFunction *MF) const = 0;
/// Return a mask of call-preserved registers for the given calling convention
/// on the current function. The mask should include all call-preserved
/// aliases. This is used by the register allocator to determine which
/// registers can be live across a call.
/// The mask is an array containing (TRI::getNumRegs()+31)/32 entries.
/// A set bit indicates that all bits of the corresponding register are
/// preserved across the function call. The bit mask is expected to be
/// sub-register complete, i.e. if A is preserved, so are all its
/// sub-registers.
/// Bits are numbered from the LSB, so the bit for physical register Reg can
/// be found as (Mask[Reg / 32] >> Reg % 32) & 1.
/// A NULL pointer means that no register mask will be used, and call
/// instructions should use implicit-def operands to indicate call clobbered
/// registers.
virtual const uint32_t *getCallPreservedMask(const MachineFunction &MF,
CallingConv::ID) const {
// The default mask clobbers everything. All targets should override.
return nullptr;
/// Return a register mask that clobbers everything.
virtual const uint32_t *getNoPreservedMask() const {
llvm_unreachable("target does not provide no preserved mask");
/// Return a list of all of the registers which are clobbered "inside" a call
/// to the given function. For example, these might be needed for PLT
/// sequences of long-branch veneers.
virtual ArrayRef<MCPhysReg>
getIntraCallClobberedRegs(const MachineFunction *MF) const {
return {};
/// Return true if all bits that are set in mask \p mask0 are also set in
/// \p mask1.
bool regmaskSubsetEqual(const uint32_t *mask0, const uint32_t *mask1) const;
/// Return all the call-preserved register masks defined for this target.
virtual ArrayRef<const uint32_t *> getRegMasks() const = 0;
virtual ArrayRef<const char *> getRegMaskNames() const = 0;
/// Returns a bitset indexed by physical register number indicating if a
/// register is a special register that has particular uses and should be
/// considered unavailable at all times, e.g. stack pointer, return address.
/// A reserved register:
/// - is not allocatable
/// - is considered always live
/// - is ignored by liveness tracking
/// It is often necessary to reserve the super registers of a reserved
/// register as well, to avoid them getting allocated indirectly. You may use
/// markSuperRegs() and checkAllSuperRegsMarked() in this case.
virtual BitVector getReservedRegs(const MachineFunction &MF) const = 0;
/// Returns false if we can't guarantee that Physreg, specified as an IR asm
/// clobber constraint, will be preserved across the statement.
virtual bool isAsmClobberable(const MachineFunction &MF,
unsigned PhysReg) const {
return true;
/// Returns true if PhysReg is unallocatable and constant throughout the
/// function. Used by MachineRegisterInfo::isConstantPhysReg().
virtual bool isConstantPhysReg(unsigned PhysReg) const { return false; }
/// Returns true if the register class is considered divergent.
virtual bool isDivergentRegClass(const TargetRegisterClass *RC) const {
return false;
/// Physical registers that may be modified within a function but are
/// guaranteed to be restored before any uses. This is useful for targets that
/// have call sequences where a GOT register may be updated by the caller
/// prior to a call and is guaranteed to be restored (also by the caller)
/// after the call.
virtual bool isCallerPreservedPhysReg(unsigned PhysReg,
const MachineFunction &MF) const {
return false;
/// This is a wrapper around getCallPreservedMask().
/// Return true if the register is preserved after the call.
virtual bool isCalleeSavedPhysReg(unsigned PhysReg,
const MachineFunction &MF) const;
/// Prior to adding the live-out mask to a stackmap or patchpoint
/// instruction, provide the target the opportunity to adjust it (mainly to
/// remove pseudo-registers that should be ignored).
virtual void adjustStackMapLiveOutMask(uint32_t *Mask) const {}
/// Return a super-register of the specified register
/// Reg so its sub-register of index SubIdx is Reg.
unsigned getMatchingSuperReg(unsigned Reg, unsigned SubIdx,
const TargetRegisterClass *RC) const {
return MCRegisterInfo::getMatchingSuperReg(Reg, SubIdx, RC->MC);
/// Return a subclass of the specified register
/// class A so that each register in it has a sub-register of the
/// specified sub-register index which is in the specified register class B.
/// TableGen will synthesize missing A sub-classes.
virtual const TargetRegisterClass *
getMatchingSuperRegClass(const TargetRegisterClass *A,
const TargetRegisterClass *B, unsigned Idx) const;
// For a copy-like instruction that defines a register of class DefRC with
// subreg index DefSubReg, reading from another source with class SrcRC and
// subregister SrcSubReg return true if this is a preferable copy
// instruction or an earlier use should be used.
virtual bool shouldRewriteCopySrc(const TargetRegisterClass *DefRC,
unsigned DefSubReg,
const TargetRegisterClass *SrcRC,
unsigned SrcSubReg) const;
/// Returns the largest legal sub-class of RC that
/// supports the sub-register index Idx.
/// If no such sub-class exists, return NULL.
/// If all registers in RC already have an Idx sub-register, return RC.
/// TableGen generates a version of this function that is good enough in most
/// cases. Targets can override if they have constraints that TableGen
/// doesn't understand. For example, the x86 sub_8bit sub-register index is
/// supported by the full GR32 register class in 64-bit mode, but only by the
/// GR32_ABCD regiister class in 32-bit mode.
/// TableGen will synthesize missing RC sub-classes.
virtual const TargetRegisterClass *
getSubClassWithSubReg(const TargetRegisterClass *RC, unsigned Idx) const {
assert(Idx == 0 && "Target has no sub-registers");
return RC;
/// Return the subregister index you get from composing
/// two subregister indices.
/// The special null sub-register index composes as the identity.
/// If R:a:b is the same register as R:c, then composeSubRegIndices(a, b)
/// returns c. Note that composeSubRegIndices does not tell you about illegal
/// compositions. If R does not have a subreg a, or R:a does not have a subreg
/// b, composeSubRegIndices doesn't tell you.
/// The ARM register Q0 has two D subregs dsub_0:D0 and dsub_1:D1. It also has
/// ssub_0:S0 - ssub_3:S3 subregs.
/// If you compose subreg indices dsub_1, ssub_0 you get ssub_2.
unsigned composeSubRegIndices(unsigned a, unsigned b) const {
if (!a) return b;
if (!b) return a;
return composeSubRegIndicesImpl(a, b);
/// Transforms a LaneMask computed for one subregister to the lanemask that
/// would have been computed when composing the subsubregisters with IdxA
/// first. @sa composeSubRegIndices()
LaneBitmask composeSubRegIndexLaneMask(unsigned IdxA,
LaneBitmask Mask) const {
if (!IdxA)
return Mask;
return composeSubRegIndexLaneMaskImpl(IdxA, Mask);
/// Transform a lanemask given for a virtual register to the corresponding
/// lanemask before using subregister with index \p IdxA.
/// This is the reverse of composeSubRegIndexLaneMask(), assuming Mask is a
/// valie lane mask (no invalid bits set) the following holds:
/// X0 = composeSubRegIndexLaneMask(Idx, Mask)
/// X1 = reverseComposeSubRegIndexLaneMask(Idx, X0)
/// => X1 == Mask
LaneBitmask reverseComposeSubRegIndexLaneMask(unsigned IdxA,
LaneBitmask LaneMask) const {
if (!IdxA)
return LaneMask;
return reverseComposeSubRegIndexLaneMaskImpl(IdxA, LaneMask);
/// Debugging helper: dump register in human readable form to dbgs() stream.
static void dumpReg(unsigned Reg, unsigned SubRegIndex = 0,
const TargetRegisterInfo* TRI = nullptr);
/// Overridden by TableGen in targets that have sub-registers.
virtual unsigned composeSubRegIndicesImpl(unsigned, unsigned) const {
llvm_unreachable("Target has no sub-registers");
/// Overridden by TableGen in targets that have sub-registers.
virtual LaneBitmask
composeSubRegIndexLaneMaskImpl(unsigned, LaneBitmask) const {
llvm_unreachable("Target has no sub-registers");
virtual LaneBitmask reverseComposeSubRegIndexLaneMaskImpl(unsigned,
LaneBitmask) const {
llvm_unreachable("Target has no sub-registers");
/// Find a common super-register class if it exists.
/// Find a register class, SuperRC and two sub-register indices, PreA and
/// PreB, such that:
/// 1. PreA + SubA == PreB + SubB (using composeSubRegIndices()), and
/// 2. For all Reg in SuperRC: Reg:PreA in RCA and Reg:PreB in RCB, and
/// 3. SuperRC->getSize() >= max(RCA->getSize(), RCB->getSize()).
/// SuperRC will be chosen such that no super-class of SuperRC satisfies the
/// requirements, and there is no register class with a smaller spill size
/// that satisfies the requirements.
/// SubA and SubB must not be 0. Use getMatchingSuperRegClass() instead.
/// Either of the PreA and PreB sub-register indices may be returned as 0. In
/// that case, the returned register class will be a sub-class of the
/// corresponding argument register class.
/// The function returns NULL if no register class can be found.
const TargetRegisterClass*
getCommonSuperRegClass(const TargetRegisterClass *RCA, unsigned SubA,
const TargetRegisterClass *RCB, unsigned SubB,
unsigned &PreA, unsigned &PreB) const;
// Register Class Information
const RegClassInfo &getRegClassInfo(const TargetRegisterClass &RC) const {
return RCInfos[getNumRegClasses() * HwMode + RC.getID()];
/// Register class iterators
regclass_iterator regclass_begin() const { return RegClassBegin; }
regclass_iterator regclass_end() const { return RegClassEnd; }
iterator_range<regclass_iterator> regclasses() const {
return make_range(regclass_begin(), regclass_end());
unsigned getNumRegClasses() const {
return (unsigned)(regclass_end()-regclass_begin());
/// Returns the register class associated with the enumeration value.
/// See class MCOperandInfo.
const TargetRegisterClass *getRegClass(unsigned i) const {
assert(i < getNumRegClasses() && "Register Class ID out of range");
return RegClassBegin[i];
/// Returns the name of the register class.
const char *getRegClassName(const TargetRegisterClass *Class) const {
return MCRegisterInfo::getRegClassName(Class->MC);
/// Find the largest common subclass of A and B.
/// Return NULL if there is no common subclass.
const TargetRegisterClass *
getCommonSubClass(const TargetRegisterClass *A,
const TargetRegisterClass *B) const;
/// Returns a TargetRegisterClass used for pointer values.
/// If a target supports multiple different pointer register classes,
/// kind specifies which one is indicated.
virtual const TargetRegisterClass *
getPointerRegClass(const MachineFunction &MF, unsigned Kind=0) const {
llvm_unreachable("Target didn't implement getPointerRegClass!");
/// Returns a legal register class to copy a register in the specified class
/// to or from. If it is possible to copy the register directly without using
/// a cross register class copy, return the specified RC. Returns NULL if it
/// is not possible to copy between two registers of the specified class.
virtual const TargetRegisterClass *
getCrossCopyRegClass(const TargetRegisterClass *RC) const {
return RC;
/// Returns the largest super class of RC that is legal to use in the current
/// sub-target and has the same spill size.
/// The returned register class can be used to create virtual registers which
/// means that all its registers can be copied and spilled.
virtual const TargetRegisterClass *
getLargestLegalSuperClass(const TargetRegisterClass *RC,
const MachineFunction &) const {
/// The default implementation is very conservative and doesn't allow the
/// register allocator to inflate register classes.
return RC;
/// Return the register pressure "high water mark" for the specific register
/// class. The scheduler is in high register pressure mode (for the specific
/// register class) if it goes over the limit.
/// Note: this is the old register pressure model that relies on a manually
/// specified representative register class per value type.
virtual unsigned getRegPressureLimit(const TargetRegisterClass *RC,
MachineFunction &MF) const {
return 0;
/// Return a heuristic for the machine scheduler to compare the profitability
/// of increasing one register pressure set versus another. The scheduler
/// will prefer increasing the register pressure of the set which returns
/// the largest value for this function.
virtual unsigned getRegPressureSetScore(const MachineFunction &MF,
unsigned PSetID) const {
return PSetID;
/// Get the weight in units of pressure for this register class.
virtual const RegClassWeight &getRegClassWeight(
const TargetRegisterClass *RC) const = 0;
/// Returns size in bits of a phys/virtual/generic register.
unsigned getRegSizeInBits(unsigned Reg, const MachineRegisterInfo &MRI) const;
/// Get the weight in units of pressure for this register unit.
virtual unsigned getRegUnitWeight(unsigned RegUnit) const = 0;
/// Get the number of dimensions of register pressure.
virtual unsigned getNumRegPressureSets() const = 0;
/// Get the name of this register unit pressure set.
virtual const char *getRegPressureSetName(unsigned Idx) const = 0;
/// Get the register unit pressure limit for this dimension.
/// This limit must be adjusted dynamically for reserved registers.
virtual unsigned getRegPressureSetLimit(const MachineFunction &MF,
unsigned Idx) const = 0;
/// Get the dimensions of register pressure impacted by this register class.
/// Returns a -1 terminated array of pressure set IDs.
virtual const int *getRegClassPressureSets(
const TargetRegisterClass *RC) const = 0;
/// Get the dimensions of register pressure impacted by this register unit.
/// Returns a -1 terminated array of pressure set IDs.
virtual const int *getRegUnitPressureSets(unsigned RegUnit) const = 0;
/// Get a list of 'hint' registers that the register allocator should try
/// first when allocating a physical register for the virtual register
/// VirtReg. These registers are effectively moved to the front of the
/// allocation order. If true is returned, regalloc will try to only use
/// hints to the greatest extent possible even if it means spilling.
/// The Order argument is the allocation order for VirtReg's register class
/// as returned from RegisterClassInfo::getOrder(). The hint registers must
/// come from Order, and they must not be reserved.
/// The default implementation of this function will only add target
/// independent register allocation hints. Targets that override this
/// function should typically call this default implementation as well and
/// expect to see generic copy hints added.
virtual bool getRegAllocationHints(unsigned VirtReg,
ArrayRef<MCPhysReg> Order,
SmallVectorImpl<MCPhysReg> &Hints,
const MachineFunction &MF,
const VirtRegMap *VRM = nullptr,
const LiveRegMatrix *Matrix = nullptr)
/// A callback to allow target a chance to update register allocation hints
/// when a register is "changed" (e.g. coalesced) to another register.
/// e.g. On ARM, some virtual registers should target register pairs,
/// if one of pair is coalesced to another register, the allocation hint of
/// the other half of the pair should be changed to point to the new register.
virtual void updateRegAllocHint(unsigned Reg, unsigned NewReg,
MachineFunction &MF) const {
// Do nothing.
/// Allow the target to reverse allocation order of local live ranges. This
/// will generally allocate shorter local live ranges first. For targets with
/// many registers, this could reduce regalloc compile time by a large
/// factor. It is disabled by default for three reasons:
/// (1) Top-down allocation is simpler and easier to debug for targets that
/// don't benefit from reversing the order.
/// (2) Bottom-up allocation could result in poor evicition decisions on some
/// targets affecting the performance of compiled code.
/// (3) Bottom-up allocation is no longer guaranteed to optimally color.
virtual bool reverseLocalAssignment() const { return false; }
/// Allow the target to override the cost of using a callee-saved register for
/// the first time. Default value of 0 means we will use a callee-saved
/// register if it is available.
virtual unsigned getCSRFirstUseCost() const { return 0; }
/// Returns true if the target requires (and can make use of) the register
/// scavenger.
virtual bool requiresRegisterScavenging(const MachineFunction &MF) const {
return false;
/// Returns true if the target wants to use frame pointer based accesses to
/// spill to the scavenger emergency spill slot.
virtual bool useFPForScavengingIndex(const MachineFunction &MF) const {
return true;
/// Returns true if the target requires post PEI scavenging of registers for
/// materializing frame index constants.
virtual bool requiresFrameIndexScavenging(const MachineFunction &MF) const {
return false;
/// Returns true if the target requires using the RegScavenger directly for
/// frame elimination despite using requiresFrameIndexScavenging.
virtual bool requiresFrameIndexReplacementScavenging(
const MachineFunction &MF) const {
return false;
/// Returns true if the target wants the LocalStackAllocation pass to be run
/// and virtual base registers used for more efficient stack access.
virtual bool requiresVirtualBaseRegisters(const MachineFunction &MF) const {
return false;
/// Return true if target has reserved a spill slot in the stack frame of
/// the given function for the specified register. e.g. On x86, if the frame
/// register is required, the first fixed stack object is reserved as its
/// spill slot. This tells PEI not to create a new stack frame
/// object for the given register. It should be called only after
/// determineCalleeSaves().
virtual bool hasReservedSpillSlot(const MachineFunction &MF, unsigned Reg,
int &FrameIdx) const {
return false;
/// Returns true if the live-ins should be tracked after register allocation.
virtual bool trackLivenessAfterRegAlloc(const MachineFunction &MF) const {
return false;
/// True if the stack can be realigned for the target.
virtual bool canRealignStack(const MachineFunction &MF) const;
/// True if storage within the function requires the stack pointer to be
/// aligned more than the normal calling convention calls for.
/// This cannot be overriden by the target, but canRealignStack can be
/// overridden.
bool needsStackRealignment(const MachineFunction &MF) const;
/// Get the offset from the referenced frame index in the instruction,
/// if there is one.
virtual int64_t getFrameIndexInstrOffset(const MachineInstr *MI,
int Idx) const {
return 0;
/// Returns true if the instruction's frame index reference would be better
/// served by a base register other than FP or SP.
/// Used by LocalStackFrameAllocation to determine which frame index
/// references it should create new base registers for.
virtual bool needsFrameBaseReg(MachineInstr *MI, int64_t Offset) const {
return false;
/// Insert defining instruction(s) for BaseReg to be a pointer to FrameIdx
/// before insertion point I.
virtual void materializeFrameBaseRegister(MachineBasicBlock *MBB,
unsigned BaseReg, int FrameIdx,
int64_t Offset) const {
llvm_unreachable("materializeFrameBaseRegister does not exist on this "
/// Resolve a frame index operand of an instruction
/// to reference the indicated base register plus offset instead.
virtual void resolveFrameIndex(MachineInstr &MI, unsigned BaseReg,
int64_t Offset) const {
llvm_unreachable("resolveFrameIndex does not exist on this target");
/// Determine whether a given base register plus offset immediate is
/// encodable to resolve a frame index.
virtual bool isFrameOffsetLegal(const MachineInstr *MI, unsigned BaseReg,
int64_t Offset) const {
llvm_unreachable("isFrameOffsetLegal does not exist on this target");
/// Spill the register so it can be used by the register scavenger.
/// Return true if the register was spilled, false otherwise.
/// If this function does not spill the register, the scavenger
/// will instead spill it to the emergency spill slot.
virtual bool saveScavengerRegister(MachineBasicBlock &MBB,
MachineBasicBlock::iterator I,
MachineBasicBlock::iterator &UseMI,
const TargetRegisterClass *RC,
unsigned Reg) const {
return false;
/// This method must be overriden to eliminate abstract frame indices from
/// instructions which may use them. The instruction referenced by the
/// iterator contains an MO_FrameIndex operand which must be eliminated by
/// this method. This method may modify or replace the specified instruction,
/// as long as it keeps the iterator pointing at the finished product.
/// SPAdj is the SP adjustment due to call frame setup instruction.
/// FIOperandNum is the FI operand number.
virtual void eliminateFrameIndex(MachineBasicBlock::iterator MI,
int SPAdj, unsigned FIOperandNum,
RegScavenger *RS = nullptr) const = 0;
/// Return the assembly name for \p Reg.
virtual StringRef getRegAsmName(unsigned Reg) const {
// FIXME: We are assuming that the assembly name is equal to the TableGen
// name converted to lower case
// The TableGen name is the name of the definition for this register in the
// target's tablegen files. For example, the TableGen name of
// def EAX : Register <...>; is "EAX"
return StringRef(getName(Reg));
/// Subtarget Hooks
/// SrcRC and DstRC will be morphed into NewRC if this returns true.
virtual bool shouldCoalesce(MachineInstr *MI,
const TargetRegisterClass *SrcRC,
unsigned SubReg,
const TargetRegisterClass *DstRC,
unsigned DstSubReg,
const TargetRegisterClass *NewRC,
LiveIntervals &LIS) const
{ return true; }
/// Debug information queries.
/// getFrameRegister - This method should return the register used as a base
/// for values allocated in the current stack frame.
virtual Register getFrameRegister(const MachineFunction &MF) const = 0;
/// Mark a register and all its aliases as reserved in the given set.
void markSuperRegs(BitVector &RegisterSet, unsigned Reg) const;
/// Returns true if for every register in the set all super registers are part
/// of the set as well.
bool checkAllSuperRegsMarked(const BitVector &RegisterSet,
ArrayRef<MCPhysReg> Exceptions = ArrayRef<MCPhysReg>()) const;
virtual const TargetRegisterClass *
getConstrainedRegClassForOperand(const MachineOperand &MO,
const MachineRegisterInfo &MRI) const {
return nullptr;
/// Returns the physical register number of sub-register "Index"
/// for physical register RegNo. Return zero if the sub-register does not
/// exist.
inline Register getSubReg(MCRegister Reg, unsigned Idx) const {
return static_cast<const MCRegisterInfo *>(this)->getSubReg(Reg, Idx);
// SuperRegClassIterator
// Iterate over the possible super-registers for a given register class. The
// iterator will visit a list of pairs (Idx, Mask) corresponding to the
// possible classes of super-registers.
// Each bit mask will have at least one set bit, and each set bit in Mask
// corresponds to a SuperRC such that:
// For all Reg in SuperRC: Reg:Idx is in RC.
// The iterator can include (O, RC->getSubClassMask()) as the first entry which
// also satisfies the above requirement, assuming Reg:0 == Reg.
class SuperRegClassIterator {
const unsigned RCMaskWords;
unsigned SubReg = 0;
const uint16_t *Idx;
const uint32_t *Mask;
/// Create a SuperRegClassIterator that visits all the super-register classes
/// of RC. When IncludeSelf is set, also include the (0, sub-classes) entry.
SuperRegClassIterator(const TargetRegisterClass *RC,
const TargetRegisterInfo *TRI,
bool IncludeSelf = false)
: RCMaskWords((TRI->getNumRegClasses() + 31) / 32),
Idx(RC->getSuperRegIndices()), Mask(RC->getSubClassMask()) {
if (!IncludeSelf)
/// Returns true if this iterator is still pointing at a valid entry.
bool isValid() const { return Idx; }
/// Returns the current sub-register index.
unsigned getSubReg() const { return SubReg; }
/// Returns the bit mask of register classes that getSubReg() projects into
/// RC.
/// See TargetRegisterClass::getSubClassMask() for how to use it.
const uint32_t *getMask() const { return Mask; }
/// Advance iterator to the next entry.
void operator++() {
assert(isValid() && "Cannot move iterator past end.");
Mask += RCMaskWords;
SubReg = *Idx++;
if (!SubReg)
Idx = nullptr;
// BitMaskClassIterator
/// This class encapuslates the logic to iterate over bitmask returned by
/// the various RegClass related APIs.
/// E.g., this class can be used to iterate over the subclasses provided by
/// TargetRegisterClass::getSubClassMask or SuperRegClassIterator::getMask.
class BitMaskClassIterator {
/// Total number of register classes.
const unsigned NumRegClasses;
/// Base index of CurrentChunk.
/// In other words, the number of bit we read to get at the
/// beginning of that chunck.
unsigned Base = 0;
/// Adjust base index of CurrentChunk.
/// Base index + how many bit we read within CurrentChunk.
unsigned Idx = 0;
/// Current register class ID.
unsigned ID = 0;
/// Mask we are iterating over.
const uint32_t *Mask;
/// Current chunk of the Mask we are traversing.
uint32_t CurrentChunk;
/// Move ID to the next set bit.
void moveToNextID() {
// If the current chunk of memory is empty, move to the next one,
// while making sure we do not go pass the number of register
// classes.
while (!CurrentChunk) {
// Move to the next chunk.
Base += 32;
if (Base >= NumRegClasses) {
ID = NumRegClasses;
CurrentChunk = *++Mask;
Idx = Base;
// Otherwise look for the first bit set from the right
// (representation of the class ID is big endian).
// See getSubClassMask for more details on the representation.
unsigned Offset = countTrailingZeros(CurrentChunk);
// Add the Offset to the adjusted base number of this chunk: Idx.
// This is the ID of the register class.
ID = Idx + Offset;
// Consume the zeros, if any, and the bit we just read
// so that we are at the right spot for the next call.
// Do not do Offset + 1 because Offset may be 31 and 32
// will be UB for the shift, though in that case we could
// have make the chunk being equal to 0, but that would
// have introduced a if statement.
/// Move \p NumBits Bits forward in CurrentChunk.
void moveNBits(unsigned NumBits) {
assert(NumBits < 32 && "Undefined behavior spotted!");
// Consume the bit we read for the next call.
CurrentChunk >>= NumBits;
// Adjust the base for the chunk.
Idx += NumBits;
/// Create a BitMaskClassIterator that visits all the register classes
/// represented by \p Mask.
/// \pre \p Mask != nullptr
BitMaskClassIterator(const uint32_t *Mask, const TargetRegisterInfo &TRI)
: NumRegClasses(TRI.getNumRegClasses()), Mask(Mask), CurrentChunk(*Mask) {
// Move to the first ID.
/// Returns true if this iterator is still pointing at a valid entry.
bool isValid() const { return getID() != NumRegClasses; }
/// Returns the current register class ID.
unsigned getID() const { return ID; }
/// Advance iterator to the next entry.
void operator++() {
assert(isValid() && "Cannot move iterator past end.");
// This is useful when building IndexedMaps keyed on virtual registers
struct VirtReg2IndexFunctor {
using argument_type = unsigned;
unsigned operator()(unsigned Reg) const {
return Register::virtReg2Index(Reg);
/// Prints virtual and physical registers with or without a TRI instance.
/// The format is:
/// %noreg - NoRegister
/// %5 - a virtual register.
/// %5:sub_8bit - a virtual register with sub-register index (with TRI).
/// %eax - a physical register
/// %physreg17 - a physical register when no TRI instance given.
/// Usage: OS << printReg(Reg, TRI, SubRegIdx) << '\n';
Printable printReg(Register Reg, const TargetRegisterInfo *TRI = nullptr,
unsigned SubIdx = 0,
const MachineRegisterInfo *MRI = nullptr);
/// Create Printable object to print register units on a \ref raw_ostream.
/// Register units are named after their root registers:
/// al - Single root.
/// fp0~st7 - Dual roots.
/// Usage: OS << printRegUnit(Unit, TRI) << '\n';
Printable printRegUnit(unsigned Unit, const TargetRegisterInfo *TRI);
/// Create Printable object to print virtual registers and physical
/// registers on a \ref raw_ostream.
Printable printVRegOrUnit(unsigned VRegOrUnit, const TargetRegisterInfo *TRI);
/// Create Printable object to print register classes or register banks
/// on a \ref raw_ostream.
Printable printRegClassOrBank(unsigned Reg, const MachineRegisterInfo &RegInfo,
const TargetRegisterInfo *TRI);
} // end namespace llvm