Re: Code optimization only in loops

[Jean Christophe Beyler <jean.christophe.beyler@gmail.com>]

Sorry to be coming back to this problem, I'm working on many projects
at the same time at the moment.

The port actually has a shift-immediate. It actually sees it later in
the fwprop pass:

In insn 14, replacing
 (ashift:DI (reg:DI 79)
        (reg:DI 77))
 with (ashift:DI (reg:DI 79)
        (const_int 3 [0x3]))
Changed insn 14
deferring rescan insn with uid = 14.

(not the same numbers but you get the idea). I don't understand why
there is a problem here but it does seem that it is linked to the way
my port handles the calculations of addresses.

Thanks again if you have any ideas, or anything I can do to give
information or ideas,
Jc


On Fri, Jun 12, 2009 at 3:55 AM, Paolo Bonzini<paolo.bonzini@gmail.com> wrote:
> Jean Christophe Beyler wrote:
>>
>> I've gone back to this problem (since I've solved another one ;-)).
>> And I've moved forward a bit:
>>
>> It seems that if I consider an array of characters, there are no
>> longer any shifts and therefore I do get my two loads with the use of
>> an offset:
>
> The reason there are shifts instead of multiplies is that multiplications
> are canonicalized to shifts whenever possible outside addresses, because a
> shift instruction should be more efficient.
>
> The interesting dump should be fwprop which is where the address generation
> happens.
>
> From your dumps, however, the problem seems to be that you do not have a
> shift-by-immediate instruction.  You may consider adding it even though it
> does not apply to your assembly, either with define_insn_and_split or by
> loosening the predicate and keeping a "r" constraint (or whatever you're
> using now).
>
> Paolo
>