http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43814
--- Comment #10 from rguenther at suse dot de <rguenther at suse dot de> 2010-12-04 18:49:34 UTC --- On Sat, 4 Dec 2010, mkuvyrkov at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43814 > > --- Comment #9 from Maxim Kuvyrkov <mkuvyrkov at gcc dot gnu.org> 2010-12-04 > 18:09:15 UTC --- > (In reply to comment #8) > > > In the end we _should_ be able to use alignment information of the > > types used at the access (that's also more reliable as compared to > > use alignment information from pointer argument types). > > > > But we already do that in MEM_REF expansion: > > > > align = MAX (TYPE_ALIGN (TREE_TYPE (exp)), > > get_object_alignment (exp, BIGGEST_ALIGNMENT)); > > Indeed. SRC will be considered 4-byte aligned in > == > unsigned long long get_ull(const unsigned int *src) > { > unsigned long long tmp; > > tmp = src[0]; Because here the C language specifies that *src has to be properly aligned. > return tmp; > } > == > , but only 1-byte aligned in > == > unsigned long long get_ull(const unsigned int *src) > { > unsigned long long tmp; > > __builtin_memcpy(&tmp, &src[0], 8); And memcpy has to deal with unaligned memory. > return tmp; > } > == > > It seems we should really use for MEM_REFs > == > align = get_pointer_alignment (exp, BIGGEST_ALIGNMENT); > == > without relying on type alignment. Unfortunately, that will worsen code > generation even more. That was what I did originally ...
