replace do-while macros with static inline functions

replace do-while macros with static inline functions

[Prathamesh Kulkarni]

I was wondering if it was a good idea to replace do-while macros with
static inline functions returning void, where appropriate ?
By "where appropriate" I mean:
a) call to macro contains no side-effects
b) macro does not modify the arguments.
c) macro does not use any preprocessor operators (like ##)
d) macro does not get undefined or is conditionally defined.
e) macro is not type independent (use inline template for these?)
f) Any other case ?

Example:
Consider C_EXPR_APPEND macro defined in c-tree.h:

/* Append a new c_expr_t element to V.  */
#define C_EXPR_APPEND(V, ELEM) \
  do { \
    c_expr_t __elem = (ELEM); \
    vec_safe_push (V, __elem); \
  } while (0)

It is called at two places in c-parser.c:
0 c-parser.c <global> 6140 C_EXPR_APPEND (cexpr_list, expr);
1 c-parser.c <global> 6145 C_EXPR_APPEND (cexpr_list, expr);

Shall be replaced by:

static inline void
C_EXPR_APPEND( vec<c_expr_t, va_gc> * V, c_expr_t ELEM)
{
    vec_safe_push(V, ELEM);
}

I will volunteer to do it, if it's accepted.

Thanks and Regards,
Prathamesh

Re: replace do-while macros with static inline functions

[Trevor Saunders]

On Wed, Dec 11, 2013 at 08:33:03PM +0530, Prathamesh Kulkarni wrote:
> I was wondering if it was a good idea to replace do-while macros with
> static inline functions returning void, where appropriate ?
> By "where appropriate" I mean:
> a) call to macro contains no side-effects
> b) macro does not modify the arguments.
> c) macro does not use any preprocessor operators (like ##)
> d) macro does not get undefined or is conditionally defined.
> e) macro is not type independent (use inline template for these?)
> f) Any other case ?

in general I'm infavor of replacing macros with unctions / constants /
templates etc.

> Example:
> Consider C_EXPR_APPEND macro defined in c-tree.h:
> 
> /* Append a new c_expr_t element to V.  */
> #define C_EXPR_APPEND(V, ELEM) \
>   do { \
>     c_expr_t __elem = (ELEM); \
>     vec_safe_push (V, __elem); \
>   } while (0)

Its not my code, but that macro looks like a totally useless
abstruction, why not just inline the vec_safe_push() ?

Trev

> 
> It is called at two places in c-parser.c:
> 0 c-parser.c <global> 6140 C_EXPR_APPEND (cexpr_list, expr);
> 1 c-parser.c <global> 6145 C_EXPR_APPEND (cexpr_list, expr);
> 
> Shall be replaced by:
> 
> static inline void
> C_EXPR_APPEND( vec<c_expr_t, va_gc> * V, c_expr_t ELEM)
> {
>     vec_safe_push(V, ELEM);
> }
> 
> I will volunteer to do it, if it's accepted.
> 
> Thanks and Regards,
> Prathamesh

Re: replace do-while macros with static inline functions

[Diego Novillo]

Bah. Forgot to remove html.

On Fri, Dec 13, 2013 at 2:47 PM, Diego Novillo <dnovillo@google.com> wrote:
>
>
>
> On Wed, Dec 11, 2013 at 10:03 AM, Prathamesh Kulkarni
> <bilbotheelffriend@gmail.com> wrote:
>>
>> I was wondering if it was a good idea to replace do-while macros with
>> static inline functions returning void, where appropriate ?
>> By "where appropriate" I mean:
>> a) call to macro contains no side-effects
>> b) macro does not modify the arguments.
>> c) macro does not use any preprocessor operators (like ##)
>> d) macro does not get undefined or is conditionally defined.
>> e) macro is not type independent (use inline template for these?)
>> f) Any other case ?
>>
>> Example:
>> Consider C_EXPR_APPEND macro defined in c-tree.h:
>>
>> /* Append a new c_expr_t element to V.  */
>> #define C_EXPR_APPEND(V, ELEM) \
>>   do { \
>>     c_expr_t __elem = (ELEM); \
>>     vec_safe_push (V, __elem); \
>>   } while (0)
>>
>
> Yes, it's a good idea.  One thing you will likely need to do, however, is to
> add some of the replaced functions into gdb's list of ignored inline
> functions. Some folks are used to gdb stepping over macro calls when 's' is
> used.
>
> Not all macros need to be turned into functions. Some can be completely
> removed (Trevor mentions an example in his reply).
>
>
> Diego.

Re: replace do-while macros with static inline functions

[Ondřej Bílka]

On Fri, Dec 13, 2013 at 02:42:23PM -0500, Trevor Saunders wrote:
> On Wed, Dec 11, 2013 at 08:33:03PM +0530, Prathamesh Kulkarni wrote:
> > I was wondering if it was a good idea to replace do-while macros with
> > static inline functions returning void, where appropriate ?
> > By "where appropriate" I mean:
> > a) call to macro contains no side-effects
> > b) macro does not modify the arguments.
> > c) macro does not use any preprocessor operators (like ##)
> > d) macro does not get undefined or is conditionally defined.
> > e) macro is not type independent (use inline template for these?)
> > f) Any other case ?
> 
> in general I'm infavor of replacing macros with unctions / constants /
> templates etc.
> 
> > Example:
> > Consider C_EXPR_APPEND macro defined in c-tree.h:
> > 
> > /* Append a new c_expr_t element to V.  */
> > #define C_EXPR_APPEND(V, ELEM) \
> >   do { \
> >     c_expr_t __elem = (ELEM); \
> >     vec_safe_push (V, __elem); \
> >   } while (0)
> 
> Its not my code, but that macro looks like a totally useless
> abstruction, why not just inline the vec_safe_push() ?
> 
Anyway if you inline macros you typically need to use always_inline.

Quite often gcc makes mistake of not inlining these, a body looks much
larger than actual inline expansion. Which is understandable as reason
of macro could be avoiding a function call overhead. 

Re: replace do-while macros with static inline functions

[Prathamesh Kulkarni]

On Sat, Dec 14, 2013 at 1:17 AM, Diego Novillo <dnovillo@google.com> wrote:
>
>
>
> On Wed, Dec 11, 2013 at 10:03 AM, Prathamesh Kulkarni
> <bilbotheelffriend@gmail.com> wrote:
>>
>> I was wondering if it was a good idea to replace do-while macros with
>> static inline functions returning void, where appropriate ?
>> By "where appropriate" I mean:
>> a) call to macro contains no side-effects
>> b) macro does not modify the arguments.
>> c) macro does not use any preprocessor operators (like ##)
>> d) macro does not get undefined or is conditionally defined.
>> e) macro is not type independent (use inline template for these?)
>> f) Any other case ?
>>
>> Example:
>> Consider C_EXPR_APPEND macro defined in c-tree.h:
>>
>> /* Append a new c_expr_t element to V.  */
>> #define C_EXPR_APPEND(V, ELEM) \
>>   do { \
>>     c_expr_t __elem = (ELEM); \
>>     vec_safe_push (V, __elem); \
>>   } while (0)
>>
>
> Yes, it's a good idea.  One thing you will likely need to do, however, is to
> add some of the replaced functions into gdb's list of ignored inline
> functions. Some folks are used to gdb stepping over macro calls when 's' is
> used.
>
> Not all macros need to be turned into functions. Some can be completely
> removed (Trevor mentions an example in his reply).

Thanks. I shall start working on it.
>
>
> Diego.