//code...
any_type_t *retVal = function_that_runs_very_long_time(a, b, &&c, **d, &e, *f);
//other code...

//code...
any_type_t *retVal =
    TIMER(
          function_that_runs_very_long_time(a, b, &&c, **d, &e, *f),
          "TIMING FOR VALUE <%d, %d>", a, b
         );
//other code...

#define TIMER(expr, fmt_msg, ...)
({
    struct timeval before, after;
    uint64_t time_span;
    int time_span_sec, time_span_usec;
    gettimeofday(&before, NULL);
    typeof(expr) _timer_expr__ = (expr);                     // <- static if?
    gettimeofday(&after, NULL);
    time_span = (after.tv_sec * 1000000 + after.tv_usec)
              - (before.tv_sec * 1000000 + before.tv_usec);
    time_span_sec  = time_span / 1000000;
    time_span_usec = time_span % 1000000;
    TRACE(fmt_msg "n%s : %d.%d seconds",
          #expr, time_span_sec, time_span_usec, ...);
    _timer_expr__;
})

#define __type_is_void(expr) __builtin_types_compatible_p(typeof(expr), void)

#define __DO(expr)
    ({ typeof(expr) __ret; __ret = (expr); __ret; })

#define __DO_VOID(expr)
    (void) (expr)

#define DO(expr)
    __builtin_choose_expr(__type_is_void(expr),
        __DO_VOID(expr),
        __DO(expr))  # won't work

test.c:28:9: error: variable or field ‘__ret’ declared void
test.c:28:9: error: void value not ignored as it ought to be

#define __expr_or_zero(expr) __builtin_choose_expr(__type_is_void(expr), 0, (expr))

#define DO(expr)
    __builtin_choose_expr(__type_is_void(expr),
        __DO_VOID(expr),
        __DO(__expr_or_zero(expr))) # works fine!

#define TIMER(is_void, expr, fmt_msg, ...)
({
    struct timeval before, after;
    uint64_t time_span;
    int time_span_sec, time_span_usec;
    gettimeofday(&before, NULL);
    if (is_void)
        (expr)
    else
        typeof(expr) _timer_expr__ = (expr);                 // <- static if?
    gettimeofday(&after, NULL);
    time_span = (after.tv_sec * 1000000 + after.tv_usec)
              - (before.tv_sec * 1000000 + before.tv_usec);
    time_span_sec  = time_span / 1000000;
    time_span_usec = time_span % 1000000;
    TRACE(fmt_msg "n%s : %d.%d seconds",
          #expr, time_span_sec, time_span_usec, ...);
    if (!is_void)
        _timer_expr__;
})

#include <stdio.h>
#define __type_is_void(expr) _Generic((typeof(expr)*){0}, void*:1, default:0)
#define __expr_or_zero(expr) _Generic((typeof(expr)*){0}, void*:0, default:(expr))

#define DO(expr)
    _Generic((typeof(expr)*){0},
        void*:__DO_VOID(expr),
        default:__DO(__expr_or_zero(expr)))

#define __DO(expr)
    ({ typeof(expr) __ret; puts("do nonvoid"); __ret = (expr); __ret; })

#define __DO_VOID(expr)
    (void)({ puts("do void"); (void)(expr); })

void foo(void) { }
int bar(void) { return 1; }

int main(void)
{
    DO(foo());
    DO(bar());
    return 0;
}