Disallow empty function bodies

Author: marbre

mlir/lib/Dialect/EmitC/IR/EmitC.cpp

@@ -436,6 +436,10 @@ LogicalResult FuncOp::verify() {
   if (getNumResults() > 1)
     return emitOpError("requires zero or exactly one result, but has ")
            << getNumResults();
+
+  if (isExternal())
+    return emitOpError("does not support empty function bodies");
+
   return success();
 }
 

mlir/test/Dialect/EmitC/invalid_ops.mlir

@@ -321,3 +321,8 @@ func.func @return_inside_func.func(%0: i32) -> (i32) {
 
 // expected-error@+1 {{expected non-function type}}
 emitc.func @func_variadic(...)
+
+// -----
+
+// expected-error@+1 {{'emitc.func' op does not support empty function bodies}}
+emitc.func private @empty()