Re: GCC porting tutorials

["Jonas Paulsson" <d03jp@student.lth.se>]

It feels good to know that the widening mults issue has been resolved as
it was a bit of a disapointment I noted the erratic behaviour with GCC
4.4.1. Perhaps you would care to comment on what to expect as a user now,
then?

Another issue that gave me porting problems was the SIMD memory accesses,
for e g doing a wide load into two adjacent narrow registers with one
instruction. This was resolved earlier on the mailinglist to not be
handleable on RTL, so I wonder now if anything has been done for this, as
it too seems rather reasonable, just like the widening loads?

/Jonas Paulsson




> On 04/27/2010 08:41 PM, Jonas Paulsson wrote:
>
>>> I've recently been bitten by the lost-widening-multiplication-
>>> when-in-loop issue myself, and noted it for revisit Some Day.
>>> Fixing that by other means made a whopping 27% improvement for
>>> the application where I saw it: a hot loop doing a MDCT using
>>> Q31 fixed-point, where a common operation is to widen-multiply
>>> two 32-bit numbers and pick the high 32 bits of the 64-bit
>>> result (being the result divided by 2; i.e. Q30-ish for that
>>> operation).
>>>
>>> brgds, H-P
>
> Widening multiplies should work again after r158633 and 158643.  If
> there are cases that still don't work for you, please file bugzilla PRs.
>
>
> Bernd
>
>