On 3 December 2014 at 14:36, Martin Jambor <mjam...@suse.cz> wrote:
> On Wed, Dec 03, 2014 at 10:53:54AM +0000, Jay Foad wrote:
>> > Index: src/gcc/ipa-prop.h
>> > ===================================================================
>> > --- src.orig/gcc/ipa-prop.h
>> > +++ src/gcc/ipa-prop.h
>> > @@ -144,6 +144,17 @@ struct GTY(()) ipa_agg_jump_function
>> >
>> > typedef struct ipa_agg_jump_function *ipa_agg_jump_function_p;
>> >
>> > +/* Info about poiner alignments. */
>>
>> "pointer"
>>
>> > +struct GTY(()) ipa_alignment
>> > +{
>> > + /* The data fields below are valid only if known is true. */
>> > + bool known;
>>
>> Just curious: why is the "known" flag necessary? The comments for
>> ptr_info_def say that align=0 means unknown.
>
> It is necessary. In IPA-CP, when know is false, this means the
> lattice is in TOP state (i.e. once we learn something about the
> parameter, let's overwrite this), whereas when it is true and
> alignment is 0, it means it is in BOTTOM state (i.e. we know we cannot
> rely on this and never will be able to).
Can't you use align=1, misalign=0 for TOP ? This means that we don't
know anything useful about the pointer yet, just that it's a multiple
of 1 (which is trivially true for all pointers, isn't it?).
When you have vectors of these struct they will pack MUCH more nicely
without the "bool known" field.
Thanks,
Jay.
