TableGen: Explicitly forbid self-references to field members

Summary:
Otherwise, patterns like in the test case produce cryptic error
messages about fields being resolved incompletely.

Change-Id: I713c0191f00fe140ad698675803ab1f8823dc5bd

Reviewers: arsenm, craig.topper, tra, MartinO

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D44476

llvm-svn: 327850

llvm/include/llvm/TableGen/Record.h

@@ -1200,7 +1200,7 @@ public:
   Init *getBit(unsigned Bit) const override;
 
   Init *resolveReferences(Resolver &R) const override;
-  Init *Fold() const;
+  Init *Fold(Record *CurRec) const;
 
   std::string getAsString() const override {
     return Rec->getAsString() + "." + FieldName->getValue().str();

llvm/lib/TableGen/Record.cpp

@@ -1684,13 +1684,19 @@ Init *FieldInit::getBit(unsigned Bit) const {
 Init *FieldInit::resolveReferences(Resolver &R) const {
   Init *NewRec = Rec->resolveReferences(R);
   if (NewRec != Rec)
-    return FieldInit::get(NewRec, FieldName)->Fold();
+    return FieldInit::get(NewRec, FieldName)->Fold(R.getCurrentRecord());
   return const_cast<FieldInit *>(this);
 }
 
-Init *FieldInit::Fold() const {
+Init *FieldInit::Fold(Record *CurRec) const {
   if (DefInit *DI = dyn_cast<DefInit>(Rec)) {
-    Init *FieldVal = DI->getDef()->getValue(FieldName)->getValue();
+    Record *Def = DI->getDef();
+    if (Def == CurRec)
+      PrintFatalError(CurRec->getLoc(),
+                      Twine("Attempting to access field '") +
+                      FieldName->getAsUnquotedString() + "' of '" +
+                      Rec->getAsString() + "' is a forbidden self-reference");
+    Init *FieldVal = Def->getValue(FieldName)->getValue();
     if (FieldVal->isComplete())
       return FieldVal;
   }

llvm/lib/TableGen/TGParser.cpp

@@ -1943,7 +1943,7 @@ Init *TGParser::ParseValue(Record *CurRec, RecTy *ItemType, IDParseMode Mode) {
                  Result->getAsString() + "'");
         return nullptr;
       }
-      Result = FieldInit::get(Result, FieldName)->Fold();
+      Result = FieldInit::get(Result, FieldName)->Fold(CurRec);
       Lex.Lex();  // eat field name
       break;
     }

llvm/test/TableGen/self-reference-recursion.td

@@ -0,0 +1,9 @@
+// RUN: not llvm-tblgen %s 2>&1 | FileCheck %s
+// XFAIL: vg_leak
+
+class A<string self> {
+  int x = !cast<A>(self).x;
+}
+
+// CHECK: error: Attempting to access field 'x' of 'A0' is a forbidden self-reference
+def A0 : A<"A0">;