lib/CodeGen/AntiDepBreaker.h

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