On 06/10/16 12:15 +0200, Jakub Jelinek wrote:
On Thu, Oct 06, 2016 at 11:05:19AM +0100, Jonathan Wakely wrote:
>I would think that we want the same answer for bool and enums: Either
>the whole type size participates in the value representation, but only
>certain values have defined behavior (so we should return true), or
>only certain bits participate in the value representation (so we
>should return false). This is a question for the committee, but I'm
>inclined to use the INTEGER_TYPE code for BOOLEAN_TYPE and
>ENUMERAL_TYPE as well, since we don't mask off the other bits when
>loading one of these types.
Yes, my new, slightly improved understanding is that if the front-end
always did a mask operation when accessing enumeration types and bool
then the bits outside its valid range of values would be padding. They
would not contribute to its value if set to non-zero values e.g. by
memset. But since we just load those values without masking, and rely
on a well-defined program not to set bits outside the valid range, we
should return true for those types.
And if bool is always implemented as load of byte and comparison against 0,
then the other bits wouldn't be padding, they would participate in the
value, but it would mean the representation of true is not unique.
But as we do sometimes comparison, sometimes masking and sometimes neither,
the behavior with values other than 0/1 is really not well defined, they
just shouldn't appear in valid programs.
So, shall I just return true for INTEGER_TYPE/BOOLEAN_TYPE/ENUMERAL_TYPE
as well as POINTER_TYPE/REFERENCE_TYPE, and if some target needs something
different, add (later on if the need arises or right away?) a target hook
where target can override.
That makes sense to me.
