[llvm-tblgen] Support conditional definitions using !casts clauses

This is a follow on to D145108. This started as simply fixing the crash on an error case reported against that change, but I think this also ends up fixing the original reported issue (#49830) as well. More accurately, D145108 fixed the case where the cast resolves to an existing record, and this change fixes the case where the named record doesn't exist.

Differential Revision: https://reviews.llvm.org/D145711

Author: preames

llvm/lib/TableGen/Record.cpp

@@ -800,37 +800,40 @@ Init *UnOpInit::Fold(Record *CurRec, bool IsFinal) const {
 
     } else if (isa<RecordRecTy>(getType())) {
       if (StringInit *Name = dyn_cast<StringInit>(LHS)) {
-        if (!CurRec && !IsFinal)
-          break;
-        assert(CurRec && "NULL pointer");
-        Record *D;
-
-        // Self-references are allowed, but their resolution is delayed until
-        // the final resolve to ensure that we get the correct type for them.
-        auto *Anonymous = dyn_cast<AnonymousNameInit>(CurRec->getNameInit());
-        if (Name == CurRec->getNameInit() ||
-            (Anonymous && Name == Anonymous->getNameInit())) {
-          if (!IsFinal)
-            break;
-          D = CurRec;
-        } else {
-          D = CurRec->getRecords().getDef(Name->getValue());
-          if (!D) {
-            if (IsFinal)
-              PrintFatalError(CurRec->getLoc(),
-                              Twine("Undefined reference to record: '") +
-                              Name->getValue() + "'\n");
-            break;
+        Record *D = RK.getDef(Name->getValue());
+        if (!D && CurRec) {
+          // Self-references are allowed, but their resolution is delayed until
+          // the final resolve to ensure that we get the correct type for them.
+          auto *Anonymous = dyn_cast<AnonymousNameInit>(CurRec->getNameInit());
+          if (Name == CurRec->getNameInit() ||
+              (Anonymous && Name == Anonymous->getNameInit())) {
+            if (!IsFinal)
+              break;
+            D = CurRec;
           }
         }
 
+        auto PrintFatalErrorHelper = [CurRec](const Twine &T) {
+          if (CurRec)
+            PrintFatalError(CurRec->getLoc(), T);
+          else
+            PrintFatalError(T);
+        };
+
+        if (!D) {
+          if (IsFinal) {
+            PrintFatalErrorHelper(Twine("Undefined reference to record: '") +
+                                  Name->getValue() + "'\n");
+          }
+          break;
+        }
+
         DefInit *DI = DefInit::get(D);
         if (!DI->getType()->typeIsA(getType())) {
-          PrintFatalError(CurRec->getLoc(),
-                          Twine("Expected type '") +
-                          getType()->getAsString() + "', got '" +
-                          DI->getType()->getAsString() + "' in: " +
-                          getAsString() + "\n");
+          PrintFatalErrorHelper(Twine("Expected type '") +
+                                getType()->getAsString() + "', got '" +
+                                DI->getType()->getAsString() + "' in: " +
+                                getAsString() + "\n");
         }
         return DI;
       }

llvm/test/TableGen/if-unresolved-cast.td

@@ -0,0 +1,8 @@
+// RUN: not llvm-tblgen %s 2>&1 | FileCheck %s
+// XFAIL: vg_leak
+
+class A { int x; }
+
+// CHECK: Undefined reference to record: ''
+if !cast<A>("").x then
+  def x;