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