[patch] Fix ICE on unaligned record field

[Eric Botcazou]

> Note that I think the place of the check is unfortunate as you for example
> will not remove the argument if it is unused.  In fact I'm not yet sure
> what transform exactly we are disabling.  I am guessing we are
> passing an aggregate by value that resides at a bit-aligned offset
> of some outer object:
> 
>   foo (x.aggr);
> 
> and the function then does
> 
> foo (Aggr a)
> {
>   int i = a.foo;
> ...
> }
> 
> thus use only a part of the aggregate.  Then IPA SRA would like to
> pass x.aggr.foo instead of x.aggr and thus tries to materialize a
> load from x.aggr.foo at all callers but fails to do that in a valid way.

Right, it's the usual MEM_EXPR business creating ADDR_EXPRs out of nowhere and 
miserably failing on something not addressable.

> Erics fix did, at all callers
> 
>   Aggr tem = x.aggr;
>   foo (tem.foo);
> 
> ?

Yes, because the code wants to take &tem afterwards.

> While we should be able to simply do
> 
>   foo (BIT_FIELD_REF <x.aggr, .....>)
> 
> with the appropriate bit offset and size?  (if that's of register type
> you need to do the load in a separate stmt of couse).
> 
> Thus similar to Erics fix but avoiding the aggregate copy.

Yes, that should be doable, but I'm not sure it's worth the hassle.

-- 
Eric Botcazou