1 //===- llvm/CodeGen/AntiDepBreaker.h - Anti-Dependence Breaking -*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the AntiDepBreaker class, which implements
10 // anti-dependence breaking heuristics for post-register-allocation scheduling.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_CODEGEN_ANTIDEPBREAKER_H
15 #define LLVM_CODEGEN_ANTIDEPBREAKER_H
16 
17 #include "llvm/ADT/iterator_range.h"
18 #include "llvm/CodeGen/MachineBasicBlock.h"
19 #include "llvm/CodeGen/MachineInstr.h"
20 #include "llvm/CodeGen/TargetSubtargetInfo.h"
21 #include "llvm/Support/Compiler.h"
22 #include <cassert>
23 #include <utility>
24 #include <vector>
25 
26 namespace llvm {
27 
28 class RegisterClassInfo;
29 
30 /// This class works in conjunction with the post-RA scheduler to rename
31 /// registers to break register anti-dependencies (WAR hazards).
32 class AntiDepBreaker {
33 public:
34   using DbgValueVector =
35       std::vector<std::pair<MachineInstr *, MachineInstr *>>;
36 
37   virtual ~AntiDepBreaker();
38 
39   /// Initialize anti-dep breaking for a new basic block.
40   virtual void StartBlock(MachineBasicBlock *BB) = 0;
41 
42   /// Identifiy anti-dependencies within a basic-block region and break them by
43   /// renaming registers. Return the number of anti-dependencies broken.
44   virtual unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits,
45                                          MachineBasicBlock::iterator Begin,
46                                          MachineBasicBlock::iterator End,
47                                          unsigned InsertPosIndex,
48                                          DbgValueVector &DbgValues) = 0;
49 
50   /// Update liveness information to account for the current
51   /// instruction, which will not be scheduled.
52   virtual void Observe(MachineInstr &MI, unsigned Count,
53                        unsigned InsertPosIndex) = 0;
54 
55   /// Finish anti-dep breaking for a basic block.
56   virtual void FinishBlock() = 0;
57 
58   /// Update DBG_VALUE or DBG_PHI if dependency breaker is updating
59   /// other machine instruction to use NewReg.
UpdateDbgValue(MachineInstr & MI,unsigned OldReg,unsigned NewReg)60   void UpdateDbgValue(MachineInstr &MI, unsigned OldReg, unsigned NewReg) {
61     if (MI.isDebugValue()) {
62       if (MI.getDebugOperand(0).isReg() &&
63           MI.getDebugOperand(0).getReg() == OldReg)
64         MI.getDebugOperand(0).setReg(NewReg);
65     } else if (MI.isDebugPHI()) {
66       if (MI.getOperand(0).isReg() &&
67           MI.getOperand(0).getReg() == OldReg)
68         MI.getOperand(0).setReg(NewReg);
69     } else {
70       llvm_unreachable("MI is not DBG_VALUE / DBG_PHI!");
71     }
72   }
73 
74   /// Update all DBG_VALUE instructions that may be affected by the dependency
75   /// breaker's update of ParentMI to use NewReg.
UpdateDbgValues(const DbgValueVector & DbgValues,MachineInstr * ParentMI,unsigned OldReg,unsigned NewReg)76   void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI,
77                        unsigned OldReg, unsigned NewReg) {
78     // The following code is dependent on the order in which the DbgValues are
79     // constructed in ScheduleDAGInstrs::buildSchedGraph.
80     MachineInstr *PrevDbgMI = nullptr;
81     for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) {
82       MachineInstr *PrevMI = DV.second;
83       if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) {
84         MachineInstr *DbgMI = DV.first;
85         UpdateDbgValue(*DbgMI, OldReg, NewReg);
86         PrevDbgMI = DbgMI;
87       } else if (PrevDbgMI) {
88         break; // If no match and already found a DBG_VALUE, we're done.
89       }
90     }
91   }
92 };
93 
94 AntiDepBreaker *createAggressiveAntiDepBreaker(
95     MachineFunction &MFi, const RegisterClassInfo &RCI,
96     TargetSubtargetInfo::RegClassVector &CriticalPathRCs);
97 
98 AntiDepBreaker *createCriticalAntiDepBreaker(MachineFunction &MFi,
99                                              const RegisterClassInfo &RCI);
100 
101 } // end namespace llvm
102 
103 #endif // LLVM_CODEGEN_ANTIDEPBREAKER_H
104