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Date: Tue, 01 Sep 2009 02:20:00 -0000
Message-ID: <c568a2600908311920s22d4db28obecbf66614356bca@mail.gmail.com>
Subject: Re: Bit fields
From: Jean Christophe Beyler <jean.christophe.beyler@gmail.com>
To: Richard Henderson <rth@redhat.com>
Cc: Ian Lance Taylor <iant@google.com>, gcc@gcc.gnu.org
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On Mon, Aug 31, 2009 at 5:27 PM, Richard Henderson<rth@redhat.com> wrote:
> On 08/31/2009 02:07 PM, Jean Christophe Beyler wrote:
>>
>> I am going to try this but shouldn't it be :
>>
>> (set (reg:QI new-scratch))
>> =A0 =A0 =A0 (zero_extract:DI ...))
>
> No.

Ok, I think I understand why not:

>> (insn 9 8 10 3 struct4.c:24 (set (subreg:DI (reg:QI 76) 0)
>>         (zero_extract:DI (reg:DI 75)
>>             (const_int 1 [0x1])
>>             (const_int 0 [0x0]))) -1 (nil))

Is basically saying :

(set (reg:DI new-scratch)
        (zero_extract:DI (reg:DI 75)
            (const_int 1 [0x1])
            (const_int 0 [0x0]))) -1 (nil))

and then apply the subreg:

(set (reg:QI 76) (subreg:QI (reg:DI new-scratch)))

which is what you were saying. I was reading the subreg the other way aroun=
d.

>
>> Any ideas?
>
> Nope. =A0You'll have to debug it.
>

Ok, is it normal to see a ashift with a negative value though or is
this already sign of a (potentially) different problem?

Thanks again and sorry about the random questions,
Jc