LLVM  10.0.0svn
MIRVRegNamerUtils.h
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1 
2 //===------------ MIRVRegNamerUtils.h - MIR VReg Renaming Utilities -------===//
3 //
4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // See https://llvm.org/LICENSE.txt for license information.
6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // The purpose of these utilities is to abstract out parts of the MIRCanon pass
11 // that are responsible for renaming virtual registers with the purpose of
12 // sharing code with a MIRVRegNamer pass that could be the analog of the
13 // opt -instnamer pass.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #ifndef LLVM_LIB_CODEGEN_MIRVREGNAMERUTILS_H
18 #define LLVM_LIB_CODEGEN_MIRVREGNAMERUTILS_H
19 
21 #include "llvm/ADT/STLExtras.h"
25 #include "llvm/CodeGen/Passes.h"
27 
28 #include <queue>
29 
30 namespace llvm {
31 
32 /// NamedVRegCursor - The cursor is an object that keeps track of what the next
33 /// vreg name should be. It does book keeping to determine when to skip the
34 /// index value and by how much, or if the next vreg name should be an increment
35 /// from the previous.
38 
39  /// virtualVRegNumber - Book keeping of the last vreg position.
40  unsigned virtualVRegNumber;
41 
42  /// SkipGapSize - Used to calculate a modulo amount to skip by after every
43  /// sequence of instructions starting from a given side-effecting
44  /// MachineInstruction for a given MachineBasicBlock. The general idea is that
45  /// for a given program compiled with two different opt pipelines, there
46  /// shouldn't be greater than SkipGapSize difference in how many vregs are in
47  /// play between the two and for every def-use graph of vregs we rename we
48  /// will round up to the next SkipGapSize'th number so that we have a high
49  /// change of landing on the same name for two given matching side-effects
50  /// for the two compilation outcomes.
51  const unsigned SkipGapSize;
52 
53  /// RenamedInOtherBB - VRegs that we already renamed: ie breadcrumbs.
54  std::vector<Register> RenamedInOtherBB;
55 
56 public:
57  NamedVRegCursor() = delete;
58  /// 1000 for the SkipGapSize was a good heuristic at the time of the writing
59  /// of the MIRCanonicalizerPass. Adjust as needed.
60  NamedVRegCursor(MachineRegisterInfo &MRI, unsigned SkipGapSize = 1000)
61  : MRI(MRI), virtualVRegNumber(0), SkipGapSize(SkipGapSize) {}
62 
63  /// SkipGapSize - Skips modulo a gap value of indices. Indices are used to
64  /// produce the next vreg name.
65  void skipVRegs();
66 
67  unsigned getVirtualVReg() const { return virtualVRegNumber; }
68 
69  /// incrementVirtualVReg - This increments an index value that us used to
70  /// create a new vreg name. This is not a Register.
71  unsigned incrementVirtualVReg(unsigned incr = 1) {
72  virtualVRegNumber += incr;
73  return virtualVRegNumber;
74  }
75 
76  /// createVirtualRegister - Given an existing vreg, create a named vreg to
77  /// take its place.
78  unsigned createVirtualRegister(unsigned VReg);
79 
80  /// renameVRegs - For a given MachineBasicBlock, scan for side-effecting
81  /// instructions, walk the def-use from each side-effecting root (in sorted
82  /// root order) and rename the encountered vregs in the def-use graph in a
83  /// canonical ordering. This method maintains book keeping for which vregs
84  /// were already renamed in RenamedInOtherBB.
85  // @return changed
86  bool renameVRegs(MachineBasicBlock *MBB);
87 };
88 
89 } // namespace llvm
90 
91 #endif
This class represents lattice values for constants.
Definition: AllocatorList.h:23
bool renameVRegs(MachineBasicBlock *MBB)
renameVRegs - For a given MachineBasicBlock, scan for side-effecting instructions, walk the def-use from each side-effecting root (in sorted root order) and rename the encountered vregs in the def-use graph in a canonical ordering.
unsigned createVirtualRegister(unsigned VReg)
createVirtualRegister - Given an existing vreg, create a named vreg to take its place.
unsigned incrementVirtualVReg(unsigned incr=1)
incrementVirtualVReg - This increments an index value that us used to create a new vreg name...
unsigned getVirtualVReg() const
void skipVRegs()
SkipGapSize - Skips modulo a gap value of indices.
NamedVRegCursor - The cursor is an object that keeps track of what the next vreg name should be...
MachineRegisterInfo - Keep track of information for virtual and physical registers, including vreg register classes, use/def chains for registers, etc.
NamedVRegCursor(MachineRegisterInfo &MRI, unsigned SkipGapSize=1000)
1000 for the SkipGapSize was a good heuristic at the time of the writing of the MIRCanonicalizerPass...