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
14 using namespace llvm;
15
16 #define DEBUG_TYPE "mir-vregnamer-utils"
17
18 static cl::opt<bool>
19 UseStableNamerHash("mir-vreg-namer-use-stable-hash", cl::init(false),
20 cl::Hidden,
21 cl::desc("Use Stable Hashing for MIR VReg Renaming"));
22
23 using VRegRenameMap = std::map<unsigned, unsigned>;
24
doVRegRenaming(const VRegRenameMap & VRM)25 bool VRegRenamer::doVRegRenaming(const VRegRenameMap &VRM) {
26 bool Changed = false;
27
28 for (const auto &E : VRM) {
29 Changed = Changed || !MRI.reg_empty(E.first);
30 MRI.replaceRegWith(E.first, E.second);
31 }
32
33 return Changed;
34 }
35
36 VRegRenameMap
getVRegRenameMap(const std::vector<NamedVReg> & VRegs)37 VRegRenamer::getVRegRenameMap(const std::vector<NamedVReg> &VRegs) {
38
39 StringMap<unsigned> VRegNameCollisionMap;
40
41 auto GetUniqueVRegName = [&VRegNameCollisionMap](const NamedVReg &Reg) {
42 if (!VRegNameCollisionMap.contains(Reg.getName()))
43 VRegNameCollisionMap[Reg.getName()] = 0;
44 const unsigned Counter = ++VRegNameCollisionMap[Reg.getName()];
45 return Reg.getName() + "__" + std::to_string(Counter);
46 };
47
48 VRegRenameMap VRM;
49 for (const auto &VReg : VRegs) {
50 const unsigned Reg = VReg.getReg();
51 VRM[Reg] = createVirtualRegisterWithLowerName(Reg, GetUniqueVRegName(VReg));
52 }
53 return VRM;
54 }
55
getInstructionOpcodeHash(MachineInstr & MI)56 std::string VRegRenamer::getInstructionOpcodeHash(MachineInstr &MI) {
57 std::string S;
58 raw_string_ostream OS(S);
59
60 if (UseStableNamerHash) {
61 auto Hash = stableHashValue(MI, /* HashVRegs */ true,
62 /* HashConstantPoolIndices */ true,
63 /* HashMemOperands */ true);
64 assert(Hash && "Expected non-zero Hash");
65 OS << format_hex_no_prefix(Hash, 16, true);
66 return OS.str();
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 (MO.getReg().isVirtual())
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 case MachineOperand::MO_DbgInstrRef:
117 return 0;
118 }
119 llvm_unreachable("Unexpected MachineOperandType.");
120 };
121
122 SmallVector<unsigned, 16> MIOperands = {MI.getOpcode(), MI.getFlags()};
123 llvm::transform(MI.uses(), std::back_inserter(MIOperands), GetHashableMO);
124
125 for (const auto *Op : MI.memoperands()) {
126 MIOperands.push_back((unsigned)Op->getSize().getValue());
127 MIOperands.push_back((unsigned)Op->getFlags());
128 MIOperands.push_back((unsigned)Op->getOffset());
129 MIOperands.push_back((unsigned)Op->getSuccessOrdering());
130 MIOperands.push_back((unsigned)Op->getAddrSpace());
131 MIOperands.push_back((unsigned)Op->getSyncScopeID());
132 MIOperands.push_back((unsigned)Op->getBaseAlign().value());
133 MIOperands.push_back((unsigned)Op->getFailureOrdering());
134 }
135
136 auto HashMI = hash_combine_range(MIOperands.begin(), MIOperands.end());
137 OS << format_hex_no_prefix(HashMI, 16, true);
138 return OS.str();
139 }
140
createVirtualRegister(unsigned VReg)141 unsigned VRegRenamer::createVirtualRegister(unsigned VReg) {
142 assert(Register::isVirtualRegister(VReg) && "Expected Virtual Registers");
143 std::string Name = getInstructionOpcodeHash(*MRI.getVRegDef(VReg));
144 return createVirtualRegisterWithLowerName(VReg, Name);
145 }
146
renameInstsInMBB(MachineBasicBlock * MBB)147 bool VRegRenamer::renameInstsInMBB(MachineBasicBlock *MBB) {
148 std::vector<NamedVReg> VRegs;
149 std::string Prefix = "bb" + std::to_string(CurrentBBNumber) + "_";
150 for (MachineInstr &Candidate : *MBB) {
151 // Don't rename stores/branches.
152 if (Candidate.mayStore() || Candidate.isBranch())
153 continue;
154 if (!Candidate.getNumOperands())
155 continue;
156 // Look for instructions that define VRegs in operand 0.
157 MachineOperand &MO = Candidate.getOperand(0);
158 // Avoid non regs, instructions defining physical regs.
159 if (!MO.isReg() || !MO.getReg().isVirtual())
160 continue;
161 VRegs.push_back(
162 NamedVReg(MO.getReg(), Prefix + getInstructionOpcodeHash(Candidate)));
163 }
164
165 return VRegs.size() ? doVRegRenaming(getVRegRenameMap(VRegs)) : false;
166 }
167
createVirtualRegisterWithLowerName(unsigned VReg,StringRef Name)168 unsigned VRegRenamer::createVirtualRegisterWithLowerName(unsigned VReg,
169 StringRef Name) {
170 std::string LowerName = Name.lower();
171 const TargetRegisterClass *RC = MRI.getRegClassOrNull(VReg);
172 return RC ? MRI.createVirtualRegister(RC, LowerName)
173 : MRI.createGenericVirtualRegister(MRI.getType(VReg), LowerName);
174 }
175