http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54965
--- Comment #3 from Siarhei Siamashka <siarhei.siamashka at gmail dot com>
2012-10-18 10:47:51 UTC ---
(In reply to comment #2)
> void combine_conjoint_xor_ca_float ()
> {
> combine_channel_t j = pd_combine_conjoint_xor, k =
> pd_combine_conjoint_xor;
> a[0] = k (0, b, 0, a[0]);
> a[0] = k (0, b, 0, a[0]);
> a[0] = k (0, b, 0, a[0]);
> a[0] = j (0, c[0], 0, a[0]);
> a[0] = k (0, c[0], 0, a[0]);
> a[0] = k (0, c[0], 0, a[0]);
> a[0] = k (0, c[0], 0, a[0]);
>
> you are using indirect function calls here, GCC in 4.6 is not smart enough
> to transform them to direct calls before inlining. Inlining of
> always-inline indirect function calls is not going to work reliably.
Does this only apply to GCC 4.6?
> Don't use always-inline or don't use indirect function calls to always-inline
> functions.
This looks like it might be really inconvenient. Pixman relies on this
functionality in a number of places by doing something like this:
void always_inline per_pixel_operation_a(...)
{
...
}
void always_inline per_pixel_operation_b(...)
{
...
}
void always_inline big_function_template(..., per_pixel_operation_ptr foo)
{
...
/* do some calls to foo() in an inner loop */
...
}
void big_function_a(...)
{
big_function_template(..., per_pixel_operation_a);
}
void big_function_b(...)
{
big_function_template(..., per_pixel_operation_b);
}
Needless to say that we want to be absolutely sure that per-pixel operations
are always inlined. Otherwise the performance gets really bad if the compiler
ever makes a bad inlining decision.
The same functionality can be probably achieved by replacing always_inline
functions with macros. But the code becomes less readable, more error prone and
somewhat more difficult to maintain.
