1 //===-- llvm/CodeGen/AllocationOrder.h - Allocation Order -*- 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 implements an allocation order for virtual registers.
11 //
12 // The preferred allocation order for a virtual register depends on allocation
13 // hints and target hooks. The AllocationOrder class encapsulates all of that.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #ifndef LLVM_LIB_CODEGEN_ALLOCATIONORDER_H
18 #define LLVM_LIB_CODEGEN_ALLOCATIONORDER_H
19 
20 #include "llvm/ADT/ArrayRef.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/MC/MCRegisterInfo.h"
23 
24 namespace llvm {
25 
26 class RegisterClassInfo;
27 class VirtRegMap;
28 class LiveRegMatrix;
29 
30 class LLVM_LIBRARY_VISIBILITY AllocationOrder {
31   SmallVector<MCPhysReg, 16> Hints;
32   ArrayRef<MCPhysReg> Order;
33   int Pos;
34 
35 public:
36   /// Create a new AllocationOrder for VirtReg.
37   /// @param VirtReg      Virtual register to allocate for.
38   /// @param VRM          Virtual register map for function.
39   /// @param RegClassInfo Information about reserved and allocatable registers.
40   AllocationOrder(unsigned VirtReg,
41                   const VirtRegMap &VRM,
42                   const RegisterClassInfo &RegClassInfo,
43                   const LiveRegMatrix *Matrix);
44 
45   /// Get the allocation order without reordered hints.
46   ArrayRef<MCPhysReg> getOrder() const { return Order; }
47 
48   /// Return the next physical register in the allocation order, or 0.
49   /// It is safe to call next() again after it returned 0, it will keep
50   /// returning 0 until rewind() is called.
51   unsigned next(unsigned Limit = 0) {
52     if (Pos < 0)
53       return Hints.end()[Pos++];
54     if (!Limit)
55       Limit = Order.size();
56     while (Pos < int(Limit)) {
57       unsigned Reg = Order[Pos++];
58       if (!isHint(Reg))
59         return Reg;
60     }
61     return 0;
62   }
63 
64   /// As next(), but allow duplicates to be returned, and stop before the
65   /// Limit'th register in the RegisterClassInfo allocation order.
66   ///
67   /// This can produce more than Limit registers if there are hints.
68   unsigned nextWithDups(unsigned Limit) {
69     if (Pos < 0)
70       return Hints.end()[Pos++];
71     if (Pos < int(Limit))
72       return Order[Pos++];
73     return 0;
74   }
75 
76   /// Start over from the beginning.
77   void rewind() { Pos = -int(Hints.size()); }
78 
79   /// Return true if the last register returned from next() was a preferred register.
80   bool isHint() const { return Pos <= 0; }
81 
82   /// Return true if PhysReg is a preferred register.
83   bool isHint(unsigned PhysReg) const { return is_contained(Hints, PhysReg); }
84 };
85 
86 } // end namespace llvm
87 
88 #endif
89