AllocationOrder.h revision 280031 
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/MC/MCRegisterInfo.h"
22
23namespace llvm {
24
25class RegisterClassInfo;
26class VirtRegMap;
27
28class AllocationOrder {
29  SmallVector<MCPhysReg, 16> Hints;
30  ArrayRef<MCPhysReg> Order;
31  int Pos;
32
33public:
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  /// Get the allocation order without reordered hints.
43  ArrayRef<MCPhysReg> getOrder() const { return Order; }
44
45  /// Return the next physical register in the allocation order, or 0.
46  /// It is safe to call next() again after it returned 0, it will keep
47  /// returning 0 until rewind() is called.
48  unsigned next(unsigned Limit = 0) {
49    if (Pos < 0)
50      return Hints.end()[Pos++];
51    if (!Limit)
52      Limit = Order.size();
53    while (Pos < int(Limit)) {
54      unsigned Reg = Order[Pos++];
55      if (!isHint(Reg))
56        return Reg;
57    }
58    return 0;
59  }
60
61  /// As next(), but allow duplicates to be returned, and stop before the
62  /// Limit'th register in the RegisterClassInfo allocation order.
63  ///
64  /// This can produce more than Limit registers if there are hints.
65  unsigned nextWithDups(unsigned Limit) {
66    if (Pos < 0)
67      return Hints.end()[Pos++];
68    if (Pos < int(Limit))
69      return Order[Pos++];
70    return 0;
71  }
72
73  /// Start over from the beginning.
74  void rewind() { Pos = -int(Hints.size()); }
75
76  /// Return true if the last register returned from next() was a preferred register.
77  bool isHint() const { return Pos <= 0; }
78
79  /// Return true if PhysReg is a preferred register.
80  bool isHint(unsigned PhysReg) const {
81    return std::find(Hints.begin(), Hints.end(), PhysReg) != Hints.end();
82  }
83};
84
85} // end namespace llvm
86
87#endif
88