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_CODEGEN_ALLOCATIONORDER_H
18 #define LLVM_CODEGEN_ALLOCATIONORDER_H
19 
20 #include "llvm/ADT/ArrayRef.h"
21 #include "llvm/MC/MCRegisterInfo.h"
22 
23 namespace llvm {
24 
25 class RegisterClassInfo;
26 class VirtRegMap;
27 
28 class AllocationOrder {
29   SmallVector<MCPhysReg, 16> Hints;
30   ArrayRef<MCPhysReg> Order;
31   int Pos;
32 
33 public:
34   /// Create a new AllocationOrder for VirtReg.
35   /// @param VirtReg      Virtual register to allocate for.
36   /// @param VRM          Virtual register map for function.
37   /// @param RegClassInfo Information about reserved and allocatable registers.
38   AllocationOrder(unsigned VirtReg,
39                   const VirtRegMap &VRM,
40                   const RegisterClassInfo &RegClassInfo);
41 
42   /// Return the next physical register in the allocation order, or 0.
43   /// It is safe to call next() again after it returned 0, it will keep
44   /// returning 0 until rewind() is called.
45   unsigned next() {
46     if (Pos < 0)
47       return Hints.end()[Pos++];
48     while (Pos < int(Order.size())) {
49       unsigned Reg = Order[Pos++];
50       if (!isHint(Reg))
51         return Reg;
52     }
53     return 0;
54   }
55 
56   /// Start over from the beginning.
57   void rewind() { Pos = -int(Hints.size()); }
58 
59   /// Return true if the last register returned from next() was a preferred register.
60   bool isHint() const { return Pos <= 0; }
61 
62   /// Return true if PhysReg is a preferred register.
63   bool isHint(unsigned PhysReg) const {
64     return std::find(Hints.begin(), Hints.end(), PhysReg) != Hints.end();
65   }
66 };
67 
68 } // end namespace llvm
69 
70 #endif
71