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