1 //===- llvm/CodeGen/AntiDepBreaker.h - Anti-Dependence Breaking -*- 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 the AntiDepBreaker class, which implements
11 // anti-dependence breaking heuristics for post-register-allocation scheduling.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #ifndef LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H
16 #define LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H
17
18 #include "llvm/ADT/iterator_range.h"
19 #include "llvm/CodeGen/MachineBasicBlock.h"
mixedOptionsTest()20 #include "llvm/CodeGen/MachineInstr.h"
21 #include "llvm/CodeGen/MachineOperand.h"
22 #include "llvm/CodeGen/ScheduleDAG.h"
23 #include "llvm/Support/Compiler.h"
24 #include <cassert>
25 #include <utility>
26 #include <vector>
27
28 namespace llvm {
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 LLVM_LIBRARY_VISIBILITY 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 if dependency breaker is updating
59 /// other machine instruction to use NewReg.
60 void UpdateDbgValue(MachineInstr &MI, unsigned OldReg, unsigned NewReg) {
61 assert(MI.isDebugValue() && "MI is not DBG_VALUE!");
62 if (MI.getOperand(0).isReg() && MI.getOperand(0).getReg() == OldReg)
63 MI.getOperand(0).setReg(NewReg);
64 }
65
66 /// Update all DBG_VALUE instructions that may be affected by the dependency
67 /// breaker's update of ParentMI to use NewReg.
68 void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI,
69 unsigned OldReg, unsigned NewReg) {
70 // The following code is dependent on the order in which the DbgValues are
71 // constructed in ScheduleDAGInstrs::buildSchedGraph.
72 MachineInstr *PrevDbgMI = nullptr;
73 for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) {
74 MachineInstr *PrevMI = DV.second;
75 if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) {
76 MachineInstr *DbgMI = DV.first;
77 UpdateDbgValue(*DbgMI, OldReg, NewReg);
78 PrevDbgMI = DbgMI;
79 } else if (PrevDbgMI) {
80 break; // If no match and already found a DBG_VALUE, we're done.
81 }
82 }
83 }
84 };
85
86 } // end namespace llvm
87
88 #endif // LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H
89