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Re: Potential bug with wide_int_storage::set_len


On Thu, Oct 13, 2016 at 10:34 AM, Andre Vieira (lists)
<Andre.SimoesDiasVieira@arm.com> wrote:
>
>> That is correct.  In RTL constants are always sign-extended from their
>> precision to HOST_BITS_PER_WIDE_INT, regardless if it is "signed" or
>> "unsigned" constant.  Whether you treat the low precision bits of the
>> constant as signed or unsigned is something encoded in the operation on it.
>>
>>       Jakub
>>
> Euhm, but then surely we must get rid of the is_sign_extended parameter
> altogether?
>
> Right now if you call that function for the same example, but with
> is_sign_extended set to true, the value will __NOT__ be sign extended.

I believe that is an optimization to cater for the difference between
the internal
storage used for INTEGER_CST trees and CONST_INT RTLs.  INTEGER_CSTs
representation is _not_ sign-extended (but it carries precision and
sign information).

Both CONST_INT and INTEGER_CST can be accessed as wide-ints without
copying the storage via some clever adaptor use but users need to care about
this subtle difference.

Richard.


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