lib/CodeGen/AntiDepBreaker.h

   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"
  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