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

[reames]

Summary

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 (https://github.com/llvm/llvm-project/issues/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.

[foad]

but I think this also ends up fixing the original reported issue (https://github.com/llvm/llvm-project/issues/49830) as well

That would be awesome! +@Joe_Nash

[foad]

I'm not competent to review the implementation but it seems to work well for me. This will let us replace lots of instances of foreach _ = BoolToList<cond>.ret in ... with if cond then ... in AMDGPU backend tablegen files.

[Joe_Nash]

This looks like it fixes 49830, and I agree with foad it is useful in the AMDGPU backend. Functionally LGTM! Thanks for working on it.

llvm/lib/TableGen/Record.cpp

if (isa<StringRecTy>(getType())) {
         return StringInit::get(RK, LHSd->getAsString());
 
       if (IntInit *LHSi = dyn_cast_or_null<IntInit>(
               LHS->convertInitializerTo(IntRecTy::get(RK))))
         return StringInit::get(RK, LHSi->getAsString());
 
     } else if (isa<RecordRecTy>(getType())) {
       if (StringInit *Name = dyn_cast<StringInit>(LHS)) {
-        if (!CurRec && !IsFinal)
-          break;
-        assert(CurRec && "NULL pointer");
-        Record *D;
-
+        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;
-        } else {
-          D = CurRec->getRecords().getDef(Name->getValue());
-          if (!D) {
-            if (IsFinal)
-              PrintFatalError(CurRec->getLoc(),
-                              Twine("Undefined reference to record: '") +
+          }
+        }
+
+        auto PrintFatalErrorHelper = [CurRec](const Twine &T) {
+          if (CurRec)
+            PrintFatalError(CurRec->getLoc(), T);
+          else
+            PrintFatalError(T);
+        };
+
+          if (IsFinal) {
+            PrintFatalErrorHelper(Twine("Undefined reference to record: '") +
                                   Name->getValue() + "'\n");
-            break;
           }
+          break;
         }
 
         DefInit *DI = DefInit::get(D);
         if (!DI->getType()->typeIsA(getType())) {
-          PrintFatalError(CurRec->getLoc(),
-                          Twine("Expected type '") +
+          PrintFatalErrorHelper(Twine("Expected type '") +
                                 getType()->getAsString() + "', got '" +
                                 DI->getType()->getAsString() + "' in: " +
                                 getAsString() + "\n");
         }
         return DI;
       }
     }
 
     if (Init *NewInit = LHS->convertInitializerTo(getType()))
       return NewInit;
     break;

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

+// 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;