Alias analysis: consoles

I've wanted to fix the alias analysis problems in our code base for a few years now. Today, while waiting for a Linux kernel compile to finish, I took at look at one of them. It is caused by this definition in console-impl.h: #ifdef ERROR_CHECK_TYPES DECLARE_INLINE_HEADER ( struct console * error_check_console_type (struct console *con, Lisp_Object sym) ) { assert (EQ (CONSOLE_TYPE (con), sym)); return con; } # define CONSOLE_TYPE_DATA(con, type) \ (*(struct type##_console **) \ &(error_check_console_type (con, Q##type))->console_data) #else # define CONSOLE_TYPE_DATA(con, type) \ (*(struct type##_console **) &((con)->console_data)) #endif That way, CONSOLE_TYPE_DATA(foo, bar) is an lvalue. However, it breaks compilations with alias analysis turned on. The way to fix this is to give up on having a single polymorphic macro that is both an rvalue and an lvalue. I'll admit it's cute, but with today's compilers, it is also dangerous. The rvalue version should look like this: #ifdef ERROR_CHECK_TYPES DECLARE_INLINE_HEADER ( struct console * error_check_console_type (struct console *con, Lisp_Object sym) ) { assert (EQ (CONSOLE_TYPE (con), sym)); return con; } # define CONSOLE_TYPE_DATA(con, type) \ ((struct type##_console *) \ (error_check_console_type (con, Q##type))->console_data) #else # define CONSOLE_TYPE_DATA(con, type) \ ((struct type##_console *) ((con)->console_data)) #endif The lvalue version is easy, since console_data is a void *, so anything can be assigned to it. I'd probably write the non-error-checking version like this: #define CONSOLE_TYPE_DATA_LVALUE(con) ((con)->console_data) or, more likely, just dispense with the stupid macro and assign to con->console_data directly. What do you other developers think? -- Jerry James http://www.jamezone.org/ _______________________________________________ XEmacs-Beta mailing list XEmacs-Beta(a)xemacs.org http://calypso.tux.org/cgi-bin/mailman/listinfo/xemacs-beta