llvm/lib/CodeGen/MIRVRegNamerUtils.cpp

   1 //===---------- MIRVRegNamerUtils.cpp - MIR VReg Renaming Utilities -------===//
   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 #include "MIRVRegNamerUtils.h"
  10 #include "llvm/CodeGen/MachineRegisterInfo.h"
  11 #include "llvm/CodeGen/MachineStableHash.h"
  12 #include "llvm/IR/Constants.h"
  13 #include "llvm/Support/Debug.h"
  14
  15 using namespace llvm;
  16
  17 #define DEBUG_TYPE "mir-vregnamer-utils"
  18
  19 static cl::opt<bool>
  20     UseStableNamerHash("mir-vreg-namer-use-stable-hash", cl::init(false),
  21                        cl::Hidden,
  22                        cl::desc("Use Stable Hashing for MIR VReg Renaming"));
  23
  24 using VRegRenameMap = std::map<unsigned, unsigned>;
  25
  26 bool VRegRenamer::doVRegRenaming(const VRegRenameMap &VRM) {
  27   bool Changed = false;
  28
  29   for (const auto &E : VRM) {
  30     Changed = Changed || !MRI.reg_empty(E.first);
  31     MRI.replaceRegWith(E.first, E.second);
  32   }
  33
  34   return Changed;
  35 }
  36
  37 VRegRenameMap
  38 VRegRenamer::getVRegRenameMap(const std::vector<NamedVReg> &VRegs) {
  39
  40   StringMap<unsigned> VRegNameCollisionMap;
  41
  42   auto GetUniqueVRegName = [&VRegNameCollisionMap](const NamedVReg &Reg) {
  43     if (VRegNameCollisionMap.find(Reg.getName()) == VRegNameCollisionMap.end())
  44       VRegNameCollisionMap[Reg.getName()] = 0;
  45     const unsigned Counter = ++VRegNameCollisionMap[Reg.getName()];
  46     return Reg.getName() + "__" + std::to_string(Counter);
  47   };
  48
  49   VRegRenameMap VRM;
  50   for (const auto &VReg : VRegs) {
  51     const unsigned Reg = VReg.getReg();
  52     VRM[Reg] = createVirtualRegisterWithLowerName(Reg, GetUniqueVRegName(VReg));
  53   }
  54   return VRM;
  55 }
  56
  57 std::string VRegRenamer::getInstructionOpcodeHash(MachineInstr &MI) {
  58   std::string S;
  59   raw_string_ostream OS(S);
  60
  61   if (UseStableNamerHash) {
  62     auto Hash = stableHashValue(MI, /* HashVRegs */ true,
  63                                 /* HashConstantPoolIndices */ true,
  64                                 /* HashMemOperands */ true);
  65     assert(Hash && "Expected non-zero Hash");
  66     return std::to_string(Hash).substr(0, 5);
  67   }
  68
  69   // Gets a hashable artifact from a given MachineOperand (ie an unsigned).
  70   auto GetHashableMO = [this](const MachineOperand &MO) -> unsigned {
  71     switch (MO.getType()) {
  72     case MachineOperand::MO_CImmediate:
  73       return hash_combine(MO.getType(), MO.getTargetFlags(),
  74                           MO.getCImm()->getZExtValue());
  75     case MachineOperand::MO_FPImmediate:
  76       return hash_combine(
  77           MO.getType(), MO.getTargetFlags(),
  78           MO.getFPImm()->getValueAPF().bitcastToAPInt().getZExtValue());
  79     case MachineOperand::MO_Register:
  80       if (Register::isVirtualRegister(MO.getReg()))
  81         return MRI.getVRegDef(MO.getReg())->getOpcode();
  82       return MO.getReg();
  83     case MachineOperand::MO_Immediate:
  84       return MO.getImm();
  85     case MachineOperand::MO_TargetIndex:
  86       return MO.getOffset() | (MO.getTargetFlags() << 16);
  87     case MachineOperand::MO_FrameIndex:
  88     case MachineOperand::MO_ConstantPoolIndex:
  89     case MachineOperand::MO_JumpTableIndex:
  90       return llvm::hash_value(MO);
  91
  92     // We could explicitly handle all the types of the MachineOperand,
  93     // here but we can just return a common number until we find a
  94     // compelling test case where this is bad. The only side effect here
  95     // is contributing to a hash collision but there's enough information
  96     // (Opcodes,other registers etc) that this will likely not be a problem.
  97
  98     // TODO: Handle the following Index/ID/Predicate cases. They can
  99     // be hashed on in a stable manner.
 100     case MachineOperand::MO_CFIIndex:
 101     case MachineOperand::MO_IntrinsicID:
 102     case MachineOperand::MO_Predicate:
 103
 104     // In the cases below we havn't found a way to produce an artifact that will
 105     // result in a stable hash, in most cases because they are pointers. We want
 106     // stable hashes because we want the hash to be the same run to run.
 107     case MachineOperand::MO_MachineBasicBlock:
 108     case MachineOperand::MO_ExternalSymbol:
 109     case MachineOperand::MO_GlobalAddress:
 110     case MachineOperand::MO_BlockAddress:
 111     case MachineOperand::MO_RegisterMask:
 112     case MachineOperand::MO_RegisterLiveOut:
 113     case MachineOperand::MO_Metadata:
 114     case MachineOperand::MO_MCSymbol:
 115     case MachineOperand::MO_ShuffleMask:
 116       return 0;
 117     }
 118     llvm_unreachable("Unexpected MachineOperandType.");
 119   };
 120
 121   SmallVector<unsigned, 16> MIOperands = {MI.getOpcode(), MI.getFlags()};
 122   llvm::transform(MI.uses(), std::back_inserter(MIOperands), GetHashableMO);
 123
 124   for (const auto *Op : MI.memoperands()) {
 125     MIOperands.push_back((unsigned)Op->getSize());
 126     MIOperands.push_back((unsigned)Op->getFlags());
 127     MIOperands.push_back((unsigned)Op->getOffset());
 128     MIOperands.push_back((unsigned)Op->getSuccessOrdering());
 129     MIOperands.push_back((unsigned)Op->getAddrSpace());
 130     MIOperands.push_back((unsigned)Op->getSyncScopeID());
 131     MIOperands.push_back((unsigned)Op->getBaseAlign().value());
 132     MIOperands.push_back((unsigned)Op->getFailureOrdering());
 133   }
 134
 135   auto HashMI = hash_combine_range(MIOperands.begin(), MIOperands.end());
 136   return std::to_string(HashMI).substr(0, 5);
 137 }
 138
 139 unsigned VRegRenamer::createVirtualRegister(unsigned VReg) {
 140   assert(Register::isVirtualRegister(VReg) && "Expected Virtual Registers");
 141   std::string Name = getInstructionOpcodeHash(*MRI.getVRegDef(VReg));
 142   return createVirtualRegisterWithLowerName(VReg, Name);
 143 }
 144
 145 bool VRegRenamer::renameInstsInMBB(MachineBasicBlock *MBB) {
 146   std::vector<NamedVReg> VRegs;
 147   std::string Prefix = "bb" + std::to_string(CurrentBBNumber) + "_";
 148   for (MachineInstr &Candidate : *MBB) {
 149     // Don't rename stores/branches.
 150     if (Candidate.mayStore() || Candidate.isBranch())
 151       continue;
 152     if (!Candidate.getNumOperands())
 153       continue;
 154     // Look for instructions that define VRegs in operand 0.
 155     MachineOperand &MO = Candidate.getOperand(0);
 156     // Avoid non regs, instructions defining physical regs.
 157     if (!MO.isReg() || !Register::isVirtualRegister(MO.getReg()))
 158       continue;
 159     VRegs.push_back(
 160         NamedVReg(MO.getReg(), Prefix + getInstructionOpcodeHash(Candidate)));
 161   }
 162
 163   return VRegs.size() ? doVRegRenaming(getVRegRenameMap(VRegs)) : false;
 164 }
 165
 166 unsigned VRegRenamer::createVirtualRegisterWithLowerName(unsigned VReg,
 167                                                          StringRef Name) {
 168   std::string LowerName = Name.lower();
 169   const TargetRegisterClass *RC = MRI.getRegClassOrNull(VReg);
 170   return RC ? MRI.createVirtualRegister(RC, LowerName)
 171             : MRI.createGenericVirtualRegister(MRI.getType(VReg), LowerName);
 172 }