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//===- RegisterClassInfo.h - Dynamic Register Class Info --------*- 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 implements the RegisterClassInfo class which provides dynamic
// information about target register classes. Callee saved and reserved
// registers depends on calling conventions and other dynamic information, so
// some things cannot be determined statically.
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/MC/MCRegisterInfo.h"
#include <cassert>
#include <cstdint>
#include <memory>
namespace llvm {
class RegisterClassInfo {
struct RCInfo {
unsigned Tag = 0;
unsigned NumRegs = 0;
bool ProperSubClass = false;
uint8_t MinCost = 0;
uint16_t LastCostChange = 0;
std::unique_ptr<MCPhysReg[]> Order;
RCInfo() = default;
operator ArrayRef<MCPhysReg>() const {
return makeArrayRef(Order.get(), NumRegs);
// Brief cached information for each register class.
std::unique_ptr<RCInfo[]> RegClass;
// Tag changes whenever cached information needs to be recomputed. An RCInfo
// entry is valid when its tag matches.
unsigned Tag = 0;
const MachineFunction *MF = nullptr;
const TargetRegisterInfo *TRI = nullptr;
// Callee saved registers of last MF. Assumed to be valid until the next
// runOnFunction() call.
// Used only to determine if an update was made to CalleeSavedAliases.
const MCPhysReg *CalleeSavedRegs = nullptr;
// Map register alias to the callee saved Register.
SmallVector<MCPhysReg, 4> CalleeSavedAliases;
// Reserved registers in the current MF.
BitVector Reserved;
std::unique_ptr<unsigned[]> PSetLimits;
// Compute all information about RC.
void compute(const TargetRegisterClass *RC) const;
// Return an up-to-date RCInfo for RC.
const RCInfo &get(const TargetRegisterClass *RC) const {
const RCInfo &RCI = RegClass[RC->getID()];
if (Tag != RCI.Tag)
return RCI;
/// runOnFunction - Prepare to answer questions about MF. This must be called
/// before any other methods are used.
void runOnMachineFunction(const MachineFunction &MF);
/// getNumAllocatableRegs - Returns the number of actually allocatable
/// registers in RC in the current function.
unsigned getNumAllocatableRegs(const TargetRegisterClass *RC) const {
return get(RC).NumRegs;
/// getOrder - Returns the preferred allocation order for RC. The order
/// contains no reserved registers, and registers that alias callee saved
/// registers come last.
ArrayRef<MCPhysReg> getOrder(const TargetRegisterClass *RC) const {
return get(RC);
/// isProperSubClass - Returns true if RC has a legal super-class with more
/// allocatable registers.
/// Register classes like GR32_NOSP are not proper sub-classes because %esp
/// is not allocatable. Similarly, tGPR is not a proper sub-class in Thumb
/// mode because the GPR super-class is not legal.
bool isProperSubClass(const TargetRegisterClass *RC) const {
return get(RC).ProperSubClass;
/// getLastCalleeSavedAlias - Returns the last callee saved register that
/// overlaps PhysReg, or 0 if Reg doesn't overlap a CalleeSavedAliases.
unsigned getLastCalleeSavedAlias(unsigned PhysReg) const {
if (PhysReg < CalleeSavedAliases.size())
return CalleeSavedAliases[PhysReg];
return 0;
/// Get the minimum register cost in RC's allocation order.
/// This is the smallest value returned by TRI->getCostPerUse(Reg) for all
/// the registers in getOrder(RC).
unsigned getMinCost(const TargetRegisterClass *RC) {
return get(RC).MinCost;
/// Get the position of the last cost change in getOrder(RC).
/// All registers in getOrder(RC).slice(getLastCostChange(RC)) will have the
/// same cost according to TRI->getCostPerUse().
unsigned getLastCostChange(const TargetRegisterClass *RC) {
return get(RC).LastCostChange;
/// Get the register unit limit for the given pressure set index.
/// RegisterClassInfo adjusts this limit for reserved registers.
unsigned getRegPressureSetLimit(unsigned Idx) const {
if (!PSetLimits[Idx])
PSetLimits[Idx] = computePSetLimit(Idx);
return PSetLimits[Idx];
unsigned computePSetLimit(unsigned Idx) const;
} // end namespace llvm