LLVM学习笔记（38）

栏目: 服务器 · 编程工具 · 发布时间: 6年前

3.5.2. 代码生成

这部分代码输出到文件X86GenInstrInfo.inc中。

3.5.2.1. 枚举常量

从InstrInfoEmitter的构造函数返回到EmitInstrInfo，接下来调用的InstrInfoEmitter::run方法来输出相关的代码。

342 void InstrInfoEmitter::run (raw_ostream &OS) {

343 emitSourceFileHeader("Target Instruction Enum Values", OS);

344 (OS);

一如既往，首先需要输出枚举常量的定义。583行的getInstructionsByEnumValue方法以名字序返回指令的CodeGenInstruction对象集（除了部分有指定次序的指令，参考一节）。

567 void InstrInfoEmitter::emitEnums (raw_ostream &OS) {

568

569 OS << "\n#ifdef GET_INSTRINFO_ENUM\n";

570 OS << "#undef GET_INSTRINFO_ENUM\n";

571

572 OS << "namespace llvm {\n\n";

573

574 CodeGenTarget Target(Records);

575

576 // We must emit the PHI opcode first...

577 std::string Namespace = Target.getInstNamespace();

578

579 if (Namespace.empty())

580 PrintFatalError("No instructions defined!");

581

582 const std::vector< const CodeGenInstruction*> &NumberedInstructions =

583 Target. getInstructionsByEnumValue ();

584

585 OS << "namespace " << Namespace << " {\n";

586 OS << " enum {\n";

587 unsigned Num = 0;

588 for ( const CodeGenInstruction *Inst : NumberedInstructions)

589 OS << " " << Inst->TheDef->getName() << "\t= " << Num++ << ",\n";

590 OS << " INSTRUCTION_LIST_END = " << NumberedInstructions.size() << "\n";

591 OS << " };\n\n";

592 OS << "namespace Sched {\n";

593 OS << " enum {\n";

594 Num = 0;

595 for ( const auto &Class : SchedModels.explicit_classes())

596 OS << " " << Class.Name << "\t= " << Num++ << ",\n";

597 OS << " SCHED_LIST_END = " << SchedModels.numInstrSchedClasses() << "\n";

598 OS << " };\n";

599 OS << "} // End Sched namespace\n";

600 OS << "} // End " << Namespace << " namespace\n";

601 OS << "} // End llvm namespace \n";

602

603 OS << "#endif // GET_INSTRINFO_ENUM\n\n";

604 }

585~591行输出代表指令的枚举常量，其输出结果是：

namespace X86 {

enum {

PHI = 0,

INLINEASM = 1,

CFI_INSTRUCTION = 2,

EH_LABEL = 3,

GC_LABEL = 4,

…

XSHA256 = 12098,

XSTORE = 12099,

XTEST = 12100,

INSTRUCTION_LIST_END = 12101

};

X86家族的指令数真是令人印象深刻（这意味着有X86家族的各种处理器一共贡献了12100个Instruction定义，为此X86使用了20个指令描述文件）。相比之下，ARM家族的指令数是2822条。

CodeGenSchedModels的容器SchedClasses保存了已知的所有调度类型，CodeGenSchedClass的来源有两种，第一种来自指令定义，包括方法从InstRW定义直接得到的类型，它们优先保存在SchedClasses容器，其他推导自ItinRW，InstRW及指令定义中的SchedVariant定义。CodeGenSchedModels成员NumInstrSchedClasses记录了第一种CodeGenSchedClass对象的个数（即597行numInstrSchedClasses方法所返回的值）。因此，592~600行输出第一种调度类型的枚举值。

namespace Sched {

enum {

NoInstrModel = 0,

IIC_AAA_WriteMicrocoded = 1,

IIC_AAD_WriteMicrocoded = 2,

IIC_AAM_WriteMicrocoded = 3,

IIC_AAS_WriteMicrocoded = 4,

…

ANDNPDrm_ANDNPSrm_ANDPDrm_ANDPSrm_ORPDrm_ORPSrm_VANDNPDYrm_VANDNPDrm_VANDNPSYrm_VANDNPSrm_VANDPDYrm_VANDPDrm_VANDPSYrm_VANDPSrm_VORPDYrm_VORPDrm_VORPSYrm_VORPSrm_VXORPDYrm_VXORPDrm_VXORPSYrm_VXORPSrm_XORPDrm_XORPSrm = 945,

VZEROUPPER = 946,

VZEROALL = 947,

LDMXCSR_VLDMXCSR = 948,

STMXCSR_VSTMXCSR = 949,

SCHED_LIST_END = 950

};

} // End Sched namespace

} // End X86 namespace

在这些定义里我们能看到一个来自InstrRW定义的调度类型，它枚举值是945。这样调度类型的名字是由对应InstRW定义所援引的指令名合成而来。另外，枚举值为1的调度类型则是一个通过指令定义得到的调度类型，这些指令使用执行步骤IIC_AAA，资源使用情况由WriteMicrocoded描述。

3.5.2.2. 操作数描述数组

在InstrInfoEmitter::run接下来输出所谓的“目标机器指令描述符”。在355行获取目标机器的指令集描述，对X86目标机器就是定义X86InstrInfo（它与基类的内容是一致的）。

InstrInfoEmitter::run（续）

346 emitSourceFileHeader("Target Instruction Descriptors", OS);

347

348 OS << "\n#ifdef GET_INSTRINFO_MC_DESC\n";

349 OS << "#undef GET_INSTRINFO_MC_DESC\n";

350

351 OS << "namespace llvm {\n\n";

352

353 CodeGenTarget &Target = CDP.getTargetInfo();

354 const std::string &TargetName = Target.getName();

355 Record *InstrInfo = Target.getInstructionSet();

356

357 // Keep track of all of the def lists we have emitted already.

358 std::map<std::vector<Record*>, unsigned> EmittedLists;

359 unsigned ListNumber = 0;

360

361 // Emit all of the instruction's implicit uses and defs.

362 for ( const CodeGenInstruction *II : Target.instructions()) {

363 Record *Inst = II->TheDef;

364 std::vector<Record*> Uses = Inst->getValueAsListOfDefs("Uses");

365 if (!Uses.empty()) {

366 unsigned &IL = EmittedLists[Uses];

367 if (!IL)(Uses, IL = ++ListNumber, OS);

368 }

369 std::vector<Record*> Defs = Inst->getValueAsListOfDefs("Defs");

370 if (!Defs.empty()) {

371 unsigned &IL = EmittedLists[Defs];

372 if (!IL) PrintDefList(Defs, IL = ++ListNumber, OS);

373 }

374 }

375

376 OperandInfoMapTy OperandInfoIDs;

377

378 // Emit all of the operand info records.

379 (OS, OperandInfoIDs);

在指令定义中Uses与Defs分别表示该指令缺省使用及改写的非操作数寄存器。首先通过下面的PrintDefList方法输出一系列ImplicitList为前缀的数组。而容器EmittedLists则关联了这些寄存器与所输出的数组（367行）。

75 static void PrintDefList ( const std::vector<Record*> &Uses,

76 unsigned Num, raw_ostream &OS) {

77 OS << "static const uint16_t ImplicitList" << Num << "[] = { ";

78 for (unsigned i = 0, e = Uses.size(); i != e; ++i)

79 OS << getQualifiedName(Uses[i]) << ", ";

80 OS << "0 };\n";

81 }

对X86目标机器，当前版本一共会输出95个数组，我们只给出几个例子，不一一列举。它们将作为后面输出的X86Insts数组元素的成员。

static const uint16_t ImplicitList1[] = { X86::FPSW, 0 };

static const uint16_t ImplicitList2[] = { X86::AX, X86::EFLAGS, 0 };

static const uint16_t ImplicitList3[] = { X86::EFLAGS, 0 };

static const uint16_t ImplicitList4[] = { X86::EAX, X86::EFLAGS, 0 };

376行的OperandInfoMapTy是std::map<std::vector<std::string>, unsigned>的typedef，它的实例OperandInfoIDs作为379行EmitOperandInfo方法的一个参数。在下面的176行看到，这个容器的第一项是不使用的。

172 void InstrInfoEmitter::EmitOperandInfo (raw_ostream &OS,

173 OperandInfoMapTy &OperandInfoIDs) {

174 // ID #0 is for no operand info.

175 unsigned OperandListNum = 0;

176 OperandInfoIDs[std::vector<std::string>()] = ++OperandListNum;

177

178 OS << "\n";

179 const CodeGenTarget &Target = CDP.getTargetInfo();

180 for ( const CodeGenInstruction *Inst : Target.instructions()) {

181 std::vector<std::string> OperandInfo =(*Inst);

182 unsigned &N = OperandInfoIDs[OperandInfo];

183 if (N != 0) continue ;

184

185 N = ++OperandListNum;

186 OS << "static const MCOperandInfo OperandInfo" << N << "[] = { ";

187 for ( const std::string &Info : OperandInfo)

188 OS << "{ " << Info << " }, ";

189 OS << "};\n";

190 }

191 }

在180行遍历所有指令定义的CodeGenInstruction 实例，以该实例为参数，在181行调用下面的GetOperandInfo方法来获取描述类型MCOperandInfo的字符串。类型MCOperandInfo是这样定义的：

56 class MCOperandInfo {

57 public :

58 /// \brief This specifies the register class enumeration of the operand

59 /// if the operand is a register. If isLookupPtrRegClass is set, then this is

60 /// an index that is passed to TargetRegisterInfo::getPointerRegClass(x) to

61 /// get a dynamic register class.

62 int16_t RegClass;

64 /// \brief These are flags from the MCOI::OperandFlags enum.

65 uint8_t Flags;

67 /// \brief Information about the type of the operand.

68 uint8_t OperandType;

69 /// \brief The lower 16 bits are used to specify which constraints are set.

70 /// The higher 16 bits are used to specify the value of constraints (4 bits

71 /// each).

72 uint32_t Constraints;

74 /// \brief Set if this operand is a pointer value and it requires a callback

75 /// to look up its register class.

76 bool isLookupPtrRegClass() const {

77 return Flags & (1 << MCOI::LookupPtrRegClass);

78 }

80 /// \brief Set if this is one of the operands that made up of the predicate

81 /// operand that controls an isPredicable() instruction.

82 bool isPredicate() const { return Flags & (1 << MCOI::Predicate); }

84 /// \brief Set if this operand is a optional def.

85 bool isOptionalDef() const { return Flags & (1 << MCOI::OptionalDef); }

86 };

这是MC用来描述指令操作数的定义，也是我们需要为每个指令操作数所输出的类型。另外，在InstrInfoEmitter::GetOperandInfo用到的嵌套类CGIOperandList::OperandInfo定义如下：

65 struct OperandInfo {

66 /// Rec - The definition this operand is declared as.

67 ///

68 Record *Rec;

70 /// Name - If this operand was assigned a symbolic name, this is it,

71 /// otherwise, it's empty.

72 std::string Name;

74 /// PrinterMethodName - The method used to print operands of this type in

75 /// the asmprinter.

76 std::string PrinterMethodName;

78 /// EncoderMethodName - The method used to get the machine operand value

79 /// for binary encoding. "getMachineOpValue" by default.

80 std::string EncoderMethodName;

82 /// OperandType - A value from MCOI::OperandType representing the type of

83 /// the operand.

84 std::string OperandType;

86 /// MIOperandNo - Currently (this is meant to be phased out), some logical

87 /// operands correspond to multiple MachineInstr operands. In the X86

88 /// target for example, one address operand is represented as 4

89 /// MachineOperands. Because of this, the operand number in the

90 /// OperandList may not match the MachineInstr operand num. Until it

91 /// does, this contains the MI operand index of this operand.

92 unsigned MIOperandNo;

93 unsigned MINumOperands; // The number of operands.

95 /// DoNotEncode - Bools are set to true in this vector for each operand in

96 /// the DisableEncoding list. These should not be emitted by the code

97 /// emitter.

98 std::vector<bool> DoNotEncode;

100 /// MIOperandInfo - Default MI operand type. Note an operand may be made

101 /// up of multiple MI operands.

102 DagInit *MIOperandInfo;

103

104 /// Constraint info for this operand. This operand can have pieces, so we

105 /// track constraint info for each.

106 std::vector<ConstraintInfo> Constraints;

107

108 OperandInfo(Record *R, const std::string &N, const std::string &PMN,

109 const std::string &EMN, const std::string &OT, unsigned MION,

110 unsigned MINO, DagInit *MIOI)

111 : Rec(R), Name(N), PrinterMethodName(PMN), EncoderMethodName(EMN),

112 OperandType(OT), MIOperandNo(MION), MINumOperands(MINO),

113 MIOperandInfo(MIOI) {}

114

115

116 /// getTiedOperand - If this operand is tied to another one, return the

117 /// other operand number. Otherwise, return -1.

118 int getTiedRegister() const {

119 for (unsigned j = 0, e = Constraints.size(); j != e; ++j) {

120 const CGIOperandList::ConstraintInfo &CI = Constraints[j];

121 if (CI.isTied()) return CI.getTiedOperand();

122 }

123 return -1;

124 }

125 };

下面91行的循环变量Op的类型也是CGIOperandList::OperandInfo。我们已经知道有些复杂指令使用的操作数是包含子操作数的。这些子操作数在.td文件里构成了以ops为操作符的一个dag值。在解析.td文件时，这个dag值被记录在相应OperandInfo对象的MIOperandInfo成员（上面102行）。缺省地，MIOperandInfo在.td文件里是(ops)，满足下面的102条件。而对于具有子操作数的情形，这些子操作数都被记录到容器OperandList里，这时OperandInfo定义里68行的Record被借用来记录子操作数的Record对象。

87 std::vector<std::string>

88 InstrInfoEmitter::GetOperandInfo ( const CodeGenInstruction &Inst) {

89 std::vector<std::string> Result;

91 for ( auto &Op : Inst.Operands) {

92 // Handle aggregate operands and normal operands the same way by expanding

93 // either case into a list of operands for this op.

94 std::vector<CGIOperandList::OperandInfo> OperandList;

96 // This might be a multiple operand thing. Targets like X86 have

97 // registers in their multi-operand operands. It may also be an anonymous

98 // operand, which has a single operand, but no declared class for the

99 // operand.

100 DagInit *MIOI = Op.MIOperandInfo;

101

102 if (!MIOI || MIOI->getNumArgs() == 0) {

103 // Single, anonymous, operand.

104 OperandList.push_back(Op);

105 } else {

106 for (unsigned j = 0, e = Op.MINumOperands; j != e; ++j) {

107 OperandList.push_back(Op);

108

109 Record *OpR = cast<DefInit>(MIOI->getArg(j))->getDef();

110 OperandList.back().Rec = OpR;

111 }

112 }

113

114 for (unsigned j = 0, e = OperandList.size(); j != e; ++j) {

115 Record *OpR = OperandList[j].Rec;

116 std::string Res;

117

118 if (OpR->isSubClassOf("RegisterOperand"))

119 OpR = OpR->getValueAsDef("RegClass");

120 if (OpR->isSubClassOf("RegisterClass"))

121 Res += getQualifiedName(OpR) + "RegClassID, ";

122 else if (OpR->isSubClassOf("PointerLikeRegClass"))

123 Res += utostr(OpR->getValueAsInt("RegClassKind")) + ", ";

124 else

125 // -1 means the operand does not have a fixed register class.

126 Res += "-1, ";

127

128 // Fill in applicable flags.

129 Res += "0";

130

131 // Ptr value whose register class is resolved via callback.

132 if (OpR->isSubClassOf("PointerLikeRegClass"))

133 Res += "|(1<<MCOI::LookupPtrRegClass)";

134

135 // Predicate operands. Check to see if the original unexpanded operand

136 // was of type PredicateOp.

137 if (Op.Rec->isSubClassOf("PredicateOp"))

138 Res += "|(1<<MCOI::Predicate)";

139

140 // Optional def operands. Check to see if the original unexpanded operand

141 // was of type OptionalDefOperand.

142 if (Op.Rec->isSubClassOf("OptionalDefOperand"))

143 Res += "|(1<<MCOI::OptionalDef)";

144

145 // Fill in operand type.

146 Res += ", ";

147 assert (!Op.OperandType.empty() && "Invalid operand type.");

148 Res += Op.OperandType;

149

150 // Fill in constraint info.

151 Res += ", ";

152

153 const CGIOperandList::ConstraintInfo &Constraint =

154 Op.Constraints[j];

155 if (Constraint.isNone())

156 Res += "0";

157 else if (Constraint.isEarlyClobber())

158 Res += "(1 << MCOI::EARLY_CLOBBER)";

159 else {

160 assert (Constraint.isTied());

161 Res += "((" + utostr(Constraint.getTiedOperand()) +

162 " << 16) | (1 << MCOI::TIED_TO))";

163 }

164

165 Result.push_back(Res);

166 }

167 }

168

169 return Result;

170 }

接下来遍历OperandList容器，根据下列枚举常量定义，输出对应的字符串。

31 namespace MCOI {

32 // Operand constraints

33 enum OperandConstraint {

34 TIED_TO = 0, // Must be allocated the same register as.

35 EARLY_CLOBBER // Operand is an early clobber register operand

36 };

38 /// \brief These are flags set on operands, but should be considered

39 /// private, all access should go through the MCOperandInfo accessors.

40 /// See the accessors for a description of what these are.

41 enum OperandFlags { LookupPtrRegClass = 0, Predicate, OptionalDef };

43 /// \brief Operands are tagged with one of the values of this enum.

44 enum OperandType {

45 OPERAND_UNKNOWN = 0,

46 OPERAND_IMMEDIATE = 1,

47 OPERAND_REGISTER = 2,

48 OPERAND_MEMORY = 3,

49 OPERAND_PCREL = 4,

50 OPERAND_FIRST_TARGET = 5

51 };

52 }

从GetOperandInfo回到EmitOperandInfo，返回值OperandInfo进而保存在OperandInfoIDs容器里作为键值，而与键值对应的则是输出MCOperandInfo的序号（0是不使用的）。因此，我们得到以下的输出（仅列举作为例子）。

static const MCOperandInfo OperandInfo2[] = { { -1, 0, MCOI::OPERAND_IMMEDIATE, 0 }, };

static const MCOperandInfo OperandInfo3[] = { { -1, 0, MCOI::OPERAND_UNKNOWN, 0 }, { -1, 0, MCOI::OPERAND_UNKNOWN, 0 }, { -1, 0, MCOI::OPERAND_IMMEDIATE, 0 }, };

static const MCOperandInfo OperandInfo4[] = { { -1, 0, MCOI::OPERAND_UNKNOWN, 0 }, { -1, 0, MCOI::OPERAND_UNKNOWN, ((0 << 16) | (1 << MCOI::TIED_TO)) }, { -1, 0, MCOI::OPERAND_UNKNOWN, 0 }, { -1, 0, MCOI::OPERAND_IMMEDIATE, 0 }, };

static const MCOperandInfo OperandInfo5[] = { { -1, 0, MCOI::OPERAND_UNKNOWN, 0 }, };

static const MCOperandInfo OperandInfo12[] = { { X86::RFP32RegClassID, 0, MCOI::OPERAND_REGISTER, 0 }, { X86::RFP32RegClassID, 0, MCOI::OPERAND_REGISTER, 0 }, };

操作数由几个子操作数构成，这个数组就有多长。另外，注意EmitOperandInfo的180行，Target.instructions()实际上是返回由getInstructionsByEnumValue方法给出的迭代器范围，因此我们遍历指令的次序还是相同的。

对X86目标机器来说，这次输出的数组有821个，这也是.td文件里给出的Operand定义的个数。它们也将作为后面输出的X86Insts数组元素的成员。

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