[TableGen] Make sure !if() is propagated across class inheritance.

[tra]

Summary

Without the patch !if() is only evaluated if it's used directly. If it's passed through more than one level of class inheritance, we end up with a reference to an anonymous record with unresolved references to the original arguments !if may have used.

The root cause of the problem is that TernOpInit::isComplete() was always returning false and that prevented use of the folded value of !if() as an initializer for the record at the next level of inheritance.

[tra]

edited a comment.

[arsenm]

LGTM

llvm/include/llvm/TableGen/Record.h

public:
   Init *getLHS() const { return LHS; }
   Init *getMHS() const { return MHS; }
   Init *getRHS() const { return RHS; }
 
   // Fold - If possible, fold this to a simpler init.  Return this if not
   // possible to fold.
   Init *Fold(Record *CurRec, MultiClass *CurMultiClass) const override;
 
-  bool isComplete() const override { return false; }
+  bool isComplete() const override {
+    return LHS->isComplete() && MHS->isComplete() && RHS->isComplete();
+  }
 
   Init *resolveReferences(Record &R, const RecordVal *RV) const override;
 
   std::string getAsString() const override;
 };
 
 /// 'Opcode' - Represent a reference to an entire variable object.
 class VarInit : public TypedInit {

llvm/test/TableGen/if.td

 // CHECK-NEXT: bits<2> val = { 0, 1 };
 // CHECK: def D32
 // CHECK-NEXT: bits<2> val = { 1, 0 };
 // CHECK: def D64
 // CHECK-NEXT: bits<2> val = { 1, 1 };
 // CHECK: def D8
 // CHECK-NEXT: bits<2> val = { 0, 0 };
 
+// Make sure !if gets evaluated throughout multiple layers of inheritance.
+class getInt<int c> {
+  int ret = !if(c, 0, 1);
+}
+class I1<int c> {
+  int i = getInt<c>.ret;
+}
+class I2<int c> : I1<c>;
+
+// CHECK: def DI1 {     // I1
+// CHECK-NEXT: int i = 0;
+def DI1: I1<1>;
+
+// CHECK: def DI2 {     // I1 I2
+// CHECK-NEXT: int i = 0;
+def DI2: I2<1>;
+
 // CHECK:      def One
 // CHECK-NEXT: list<int> first = [1, 2, 3];
 // CHECK-NEXT: list<int> rest = [1, 2, 3];
 
 // CHECK:      def OneB
 // CHECK-NEXT: list<int> vals = [1, 2, 3];
 
 // CHECK:      def Two