http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54965
--- Comment #4 from rguenther at suse dot de <rguenther at suse dot de> 2012-10-18 10:58:56 UTC --- On Thu, 18 Oct 2012, siarhei.siamashka at gmail dot com wrote: > > 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? No, that applies in general. If GCC isn't able to figure out which function is called it cannot make sure always-inline functions are always inlined. always-inline is an attribute that should be used if it is incorrect to not inline, not if that's just good for optimziation. > > 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. In the above case you probably want big_function_a to have all calls inlined. You can then conveniently use the flatten attribute: void __attribute__((flatten)) big_function_b (...) { big_function_template(..., per_pixel_operation_b); } GCC will then inline all calls in that function but not ICE when it fails to inline one case for some weird reason. Richard.
