[Heavy] Fix nested ifs in tail pos

Author: ricejasonf

heavy/lib/OpGen.cpp

@@ -877,8 +877,11 @@ mlir::Value OpGen::createIf(SourceLocation Loc, Value Cond, Value Then,
       Builder.setInsertionPointToStart(Block);
       mlir::Value Result = Visit(Value);
       Block = Builder.getBlock();
-      if (Block->empty() || !isa<ApplyOp>(Block->back()))
+      if (Result) {
+        assert(Block->empty() ||
+          !Block->back().hasTrait<mlir::OpTrait::IsTerminator>());
         create<ContOp>(Loc, Result);
+      }
     };
 
     handleBranch(Then, ThenBlock);

heavy/test/Evaluate/if.scm

@@ -103,3 +103,19 @@
 (write
   (if (null? 42) 'return-baz))
 (newline)
+
+; Should compile
+(define (maybe-literal-op* Arg)
+  (define AttrVal
+    (if (number? Arg)
+      (write (number->string Arg))
+      (if (symbol? Arg)
+        (error "oof")
+        (if (string? Arg)
+          (error "woof")
+          #f))))
+  (if AttrVal
+    'ok
+    Arg))
+; CHECK-NEXT: "5"
+(maybe-literal-op* 5)