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//===- RegAllocBase.h - basic regalloc interface and driver -----*- 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 defines the RegAllocBase class, which is the skeleton of a basic
// register allocation algorithm and interface for extending it. It provides the
// building blocks on which to construct other experimental allocators and test
// the validity of two principles:
//
// - If virtual and physical register liveness is modeled using intervals, then
// on-the-fly interference checking is cheap. Furthermore, interferences can be
// lazily cached and reused.
//
// - Register allocation complexity, and generated code performance is
// determined by the effectiveness of live range splitting rather than optimal
// coloring.
//
// Following the first principle, interfering checking revolves around the
// LiveIntervalUnion data structure.
//
// To fulfill the second principle, the basic allocator provides a driver for
// incremental splitting. It essentially punts on the problem of register
// coloring, instead driving the assignment of virtual to physical registers by
// the cost of splitting. The basic allocator allows for heuristic reassignment
// of registers, if a more sophisticated allocator chooses to do that.
//
// This framework provides a way to engineer the compile time vs. code
// quality trade-off without relying on a particular theoretical solver.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIB_CODEGEN_REGALLOCBASE_H
#define LLVM_LIB_CODEGEN_REGALLOCBASE_H
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/RegAllocCommon.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
namespace llvm {
class LiveInterval;
class LiveIntervals;
class LiveRegMatrix;
class MachineInstr;
class MachineRegisterInfo;
template<typename T> class SmallVectorImpl;
class Spiller;
class TargetRegisterInfo;
class VirtRegMap;
/// RegAllocBase provides the register allocation driver and interface that can
/// be extended to add interesting heuristics.
///
/// Register allocators must override the selectOrSplit() method to implement
/// live range splitting. They must also override enqueue/dequeue to provide an
/// assignment order.
class RegAllocBase {
virtual void anchor();
protected:
const TargetRegisterInfo *TRI = nullptr;
MachineRegisterInfo *MRI = nullptr;
VirtRegMap *VRM = nullptr;
LiveIntervals *LIS = nullptr;
LiveRegMatrix *Matrix = nullptr;
RegisterClassInfo RegClassInfo;
const RegClassFilterFunc ShouldAllocateClass;
/// Inst which is a def of an original reg and whose defs are already all
/// dead after remat is saved in DeadRemats. The deletion of such inst is
/// postponed till all the allocations are done, so its remat expr is
/// always available for the remat of all the siblings of the original reg.
SmallPtrSet<MachineInstr *, 32> DeadRemats;
RegAllocBase(const RegClassFilterFunc F = allocateAllRegClasses) :
ShouldAllocateClass(F) {}
virtual ~RegAllocBase() = default;
// A RegAlloc pass should call this before allocatePhysRegs.
void init(VirtRegMap &vrm, LiveIntervals &lis, LiveRegMatrix &mat);
// The top-level driver. The output is a VirtRegMap that us updated with
// physical register assignments.
void allocatePhysRegs();
// Include spiller post optimization and removing dead defs left because of
// rematerialization.
virtual void postOptimization();
// Get a temporary reference to a Spiller instance.
virtual Spiller &spiller() = 0;
/// enqueue - Add VirtReg to the priority queue of unassigned registers.
virtual void enqueueImpl(LiveInterval *LI) = 0;
/// enqueue - Add VirtReg to the priority queue of unassigned registers.
void enqueue(LiveInterval *LI);
/// dequeue - Return the next unassigned register, or NULL.
virtual LiveInterval *dequeue() = 0;
// A RegAlloc pass should override this to provide the allocation heuristics.
// Each call must guarantee forward progess by returning an available PhysReg
// or new set of split live virtual registers. It is up to the splitter to
// converge quickly toward fully spilled live ranges.
virtual MCRegister selectOrSplit(LiveInterval &VirtReg,
SmallVectorImpl<Register> &splitLVRs) = 0;
// Use this group name for NamedRegionTimer.
static const char TimerGroupName[];
static const char TimerGroupDescription[];
/// Method called when the allocator is about to remove a LiveInterval.
virtual void aboutToRemoveInterval(LiveInterval &LI) {}
public:
/// VerifyEnabled - True when -verify-regalloc is given.
static bool VerifyEnabled;
private:
void seedLiveRegs();
};
} // end namespace llvm
#endif // LLVM_LIB_CODEGEN_REGALLOCBASE_H
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