[TableGen] Stabilize sort in GET_SUBTARGETINFO_MACRO block

[kpn]

Summary

The sort of the elements in the GET_SUBTARGETINFO_MACRO block is done on the "Name" field of each record. This field is not guaranteed to be unique, is not guaranteed to even have a value at all, and is not used in the output anyway. Change to sort on the "Attribute" field which should be unique.

Problem spotted when lib/Target/PowerPC/PPCGenSubtargetInfo.inc changed unexpectedly.

[craig.topper]

The Attribute field isn't required to be unique. It's only unique for boolean features, but this emitter ignores non-boolean features so maybe that's ok?

[pengfei]

Makes sense to me.

[craig.topper]

llvm/include/llvm/TableGen/Record.h

2038

Probably could keep this in SubtargetEmitter.cpp? Doesn't seem generically useful.

llvm/include/llvm/TableGen/Record.h

 /// Sorting predicate to sort record pointers by their
 /// name field.
 struct LessRecordFieldName {
   bool operator()(const Record *Rec1, const Record *Rec2) const {
     return Rec1->getValueAsString("Name") < Rec2->getValueAsString("Name");
   }
 };
 
+/// Sorting predicate to sort record pointers by their
+/// FieldName field.
+struct LessRecordFieldFieldName {
+  bool operator()(const Record *Rec1, const Record *Rec2) const {
+    return Rec1->getValueAsString("FieldName") <
+           Rec2->getValueAsString("FieldName");
+  }
+};
+
 struct LessRecordRegister {
   struct RecordParts {
     SmallVector<std::pair< bool, StringRef>, 4> Parts;
 
     RecordParts(StringRef Rec) {
       if (Rec.empty())
         return;
 

llvm/utils/TableGen/SubtargetEmitter.cpp

 
 /// Emit some information about the SubtargetFeature as calls to a macro so
 /// that they can be used from C++.
 void SubtargetEmitter::EmitSubtargetInfoMacroCalls(raw_ostream &OS) {
   OS << "\n#ifdef GET_SUBTARGETINFO_MACRO\n";
 
   std::vector<Record *> FeatureList =
       Records.getAllDerivedDefinitions("SubtargetFeature");
-  llvm::sort(FeatureList, LessRecordFieldName());
+  llvm::sort(FeatureList, LessRecordFieldFieldName());
 
   for (const Record *Feature : FeatureList) {
     const StringRef FieldName = Feature->getValueAsString("FieldName");
     const StringRef Value = Feature->getValueAsString("Value");
 
     // Only handle boolean features for now, excluding BitVectors and enums.
     const bool IsBool = (Value == "false" || Value == "true") &&
                         !StringRef(FieldName).contains('[');