lib/CodeGen/RegAllocBase.h

   1 //===- RegAllocBase.h - basic regalloc interface and driver -----*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines the RegAllocBase class, which is the skeleton of a basic
  10 // register allocation algorithm and interface for extending it. It provides the
  11 // building blocks on which to construct other experimental allocators and test
  12 // the validity of two principles:
  13 //
  14 // - If virtual and physical register liveness is modeled using intervals, then
  15 // on-the-fly interference checking is cheap. Furthermore, interferences can be
  16 // lazily cached and reused.
  17 //
  18 // - Register allocation complexity, and generated code performance is
  19 // determined by the effectiveness of live range splitting rather than optimal
  20 // coloring.
  21 //
  22 // Following the first principle, interfering checking revolves around the
  23 // LiveIntervalUnion data structure.
  24 //
  25 // To fulfill the second principle, the basic allocator provides a driver for
  26 // incremental splitting. It essentially punts on the problem of register
  27 // coloring, instead driving the assignment of virtual to physical registers by
  28 // the cost of splitting. The basic allocator allows for heuristic reassignment
  29 // of registers, if a more sophisticated allocator chooses to do that.
  30 //
  31 // This framework provides a way to engineer the compile time vs. code
  32 // quality trade-off without relying on a particular theoretical solver.
  33 //
  34 //===----------------------------------------------------------------------===//
  35
  36 #ifndef LLVM_LIB_CODEGEN_REGALLOCBASE_H
  37 #define LLVM_LIB_CODEGEN_REGALLOCBASE_H
  38
  39 #include "llvm/ADT/SmallPtrSet.h"
  40 #include "llvm/CodeGen/RegisterClassInfo.h"
  41
  42 namespace llvm {
  43
  44 class LiveInterval;
  45 class LiveIntervals;
  46 class LiveRegMatrix;
  47 class MachineInstr;
  48 class MachineRegisterInfo;
  49 template<typename T> class SmallVectorImpl;
  50 class Spiller;
  51 class TargetRegisterInfo;
  52 class VirtRegMap;
  53
  54 /// RegAllocBase provides the register allocation driver and interface that can
  55 /// be extended to add interesting heuristics.
  56 ///
  57 /// Register allocators must override the selectOrSplit() method to implement
  58 /// live range splitting. They must also override enqueue/dequeue to provide an
  59 /// assignment order.
  60 class RegAllocBase {
  61   virtual void anchor();
  62
  63 protected:
  64   const TargetRegisterInfo *TRI = nullptr;
  65   MachineRegisterInfo *MRI = nullptr;
  66   VirtRegMap *VRM = nullptr;
  67   LiveIntervals *LIS = nullptr;
  68   LiveRegMatrix *Matrix = nullptr;
  69   RegisterClassInfo RegClassInfo;
  70
  71   /// Inst which is a def of an original reg and whose defs are already all
  72   /// dead after remat is saved in DeadRemats. The deletion of such inst is
  73   /// postponed till all the allocations are done, so its remat expr is
  74   /// always available for the remat of all the siblings of the original reg.
  75   SmallPtrSet<MachineInstr *, 32> DeadRemats;
  76
  77   RegAllocBase() = default;
  78   virtual ~RegAllocBase() = default;
  79
  80   // A RegAlloc pass should call this before allocatePhysRegs.
  81   void init(VirtRegMap &vrm, LiveIntervals &lis, LiveRegMatrix &mat);
  82
  83   // The top-level driver. The output is a VirtRegMap that us updated with
  84   // physical register assignments.
  85   void allocatePhysRegs();
  86
  87   // Include spiller post optimization and removing dead defs left because of
  88   // rematerialization.
  89   virtual void postOptimization();
  90
  91   // Get a temporary reference to a Spiller instance.
  92   virtual Spiller &spiller() = 0;
  93
  94   /// enqueue - Add VirtReg to the priority queue of unassigned registers.
  95   virtual void enqueue(LiveInterval *LI) = 0;
  96
  97   /// dequeue - Return the next unassigned register, or NULL.
  98   virtual LiveInterval *dequeue() = 0;
  99
 100   // A RegAlloc pass should override this to provide the allocation heuristics.
 101   // Each call must guarantee forward progess by returning an available PhysReg
 102   // or new set of split live virtual registers. It is up to the splitter to
 103   // converge quickly toward fully spilled live ranges.
 104   virtual unsigned selectOrSplit(LiveInterval &VirtReg,
 105                                  SmallVectorImpl<unsigned> &splitLVRs) = 0;
 106
 107   // Use this group name for NamedRegionTimer.
 108   static const char TimerGroupName[];
 109   static const char TimerGroupDescription[];
 110
 111   /// Method called when the allocator is about to remove a LiveInterval.
 112   virtual void aboutToRemoveInterval(LiveInterval &LI) {}
 113
 114 public:
 115   /// VerifyEnabled - True when -verify-regalloc is given.
 116   static bool VerifyEnabled;
 117
 118 private:
 119   void seedLiveRegs();
 120 };
 121
 122 } // end namespace llvm
 123
 124 #endif // LLVM_LIB_CODEGEN_REGALLOCBASE_H