[TableGen][DecoderEmitter] Outline InstructionEncoding constructor (NFC) (#154673)

It is going to grow, so it makes sense to move its definition
out of class. Instead, inline `populateInstruction()` into it.
Also, rename a couple of methods to better convey their meaning.

Author: s-barannikov

llvm/utils/TableGen/DecoderEmitter.cpp

@@ -155,21 +155,8 @@ class InstructionEncoding {
   SmallVector<OperandInfo, 16> Operands;
 
 public:
-  InstructionEncoding(const Record *EncodingDef, const CodeGenInstruction *Inst)
-      : EncodingDef(EncodingDef), Inst(Inst) {
-    const Record *InstDef = Inst->TheDef;
-
-    // Give this encoding a name.
-    if (EncodingDef != InstDef)
-      Name = (EncodingDef->getName() + Twine(':')).str();
-    Name.append(InstDef->getName());
-
-    DecoderMethod = EncodingDef->getValueAsString("DecoderMethod");
-    if (!DecoderMethod.empty())
-      HasCompleteDecoder = EncodingDef->getValueAsBit("hasCompleteDecoder");
-
-    populateEncoding();
-  }
+  InstructionEncoding(const Record *EncodingDef,
+                      const CodeGenInstruction *Inst);
 
   /// Returns the Record this encoding originates from.
   const Record *getRecord() const { return EncodingDef; }
@@ -197,9 +184,8 @@ class InstructionEncoding {
   ArrayRef<OperandInfo> getOperands() const { return Operands; }
 
 private:
-  void populateVarLenEncoding(const VarLenInst &VLI);
-  void populateFixedLenEncoding(const BitsInit &Bits);
-  void populateEncoding();
+  void parseVarLenOperands(const VarLenInst &VLI);
+  void parseFixedLenOperands(const BitsInit &Bits);
 };
 
 typedef std::vector<uint32_t> FixupList;
@@ -1899,7 +1885,7 @@ OperandInfo getOpInfo(const Record *TypeRecord) {
   return OperandInfo(findOperandDecoderMethod(TypeRecord), HasCompleteDecoder);
 }
 
-void InstructionEncoding::populateVarLenEncoding(const VarLenInst &VLI) {
+void InstructionEncoding::parseVarLenOperands(const VarLenInst &VLI) {
   SmallVector<int> TiedTo;
 
   for (const auto &[Idx, Op] : enumerate(Inst->Operands)) {
@@ -1996,7 +1982,7 @@ static void addOneOperandFields(const Record *EncodingDef, const BitsInit &Bits,
   }
 }
 
-void InstructionEncoding::populateFixedLenEncoding(const BitsInit &Bits) {
+void InstructionEncoding::parseFixedLenOperands(const BitsInit &Bits) {
   const Record &Def = *Inst->TheDef;
 
   // Gather the outputs/inputs of the instruction, so we can find their
@@ -2110,20 +2096,33 @@ void InstructionEncoding::populateFixedLenEncoding(const BitsInit &Bits) {
   }
 }
 
-void InstructionEncoding::populateEncoding() {
+InstructionEncoding::InstructionEncoding(const Record *EncodingDef,
+                                         const CodeGenInstruction *Inst)
+    : EncodingDef(EncodingDef), Inst(Inst) {
+  const Record *InstDef = Inst->TheDef;
+
+  // Give this encoding a name.
+  if (EncodingDef != InstDef)
+    Name = (EncodingDef->getName() + Twine(':')).str();
+  Name.append(InstDef->getName());
+
+  DecoderMethod = EncodingDef->getValueAsString("DecoderMethod");
+  if (!DecoderMethod.empty())
+    HasCompleteDecoder = EncodingDef->getValueAsBit("hasCompleteDecoder");
+
   const RecordVal *InstField = EncodingDef->getValue("Inst");
   if (const auto *DI = dyn_cast<DagInit>(InstField->getValue())) {
     VarLenInst VLI(DI, InstField);
     BitWidth = VLI.size();
     // If the encoding has a custom decoder, don't bother parsing the operands.
     if (DecoderMethod.empty())
-      populateVarLenEncoding(VLI);
+      parseVarLenOperands(VLI);
   } else {
     const auto *BI = cast<BitsInit>(InstField->getValue());
     BitWidth = BI->getNumBits();
     // If the encoding has a custom decoder, don't bother parsing the operands.
     if (DecoderMethod.empty())
-      populateFixedLenEncoding(*BI);
+      parseFixedLenOperands(*BI);
   }
 }