• #ponce <aliloko gmail.com> Sep 05 2009
• Jarrett Billingsley <jarrett.billingsley gmail.com> Sep 05 2009
• bearophile <bearophileHUGS lycos.com> Sep 05 2009
• Stewart Gordon <smjg_1998 yahoo.com> Sep 05 2009
• #ponce <aliloko gmail.com> Sep 07 2009
• #ponce <aliloko gmail.com> Sep 07 2009
• "Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> Sep 07 2009
• Stewart Gordon <smjg_1998 yahoo.com> Sep 07 2009
• grauzone <none example.net> Sep 09 2009
• #ponce <aliloko gmail.com> Sep 09 2009

#ponce <aliloko gmail.com> writes:

I'm currently using a lot of pointers to perform heavy computation

Has D the equivalent for C's restrict ? More generally, how does D cope with
the aliasing of pointers ? I think it's crucial for the code optimizer.

Jarrett Billingsley <jarrett.billingsley gmail.com> writes:

On Sat, Sep 5, 2009 at 3:49 AM, #ponce<aliloko gmail.com> wrote:
 I'm currently using a lot of pointers to perform heavy computation

 Has D the equivalent for C's restrict ? More generally, how does D cope with
the aliasing of pointers ? I think it's crucial for the code optimizer.


It doesn't.

bearophile <bearophileHUGS lycos.com> writes:

#ponce:
 I'm currently using a lot of pointers to perform heavy computation  Has D the
equivalent for C's restrict ? More generally, how does D cope with the aliasing
of pointers ? I think it's crucial for the code optimizer.<


DMD probably just doesn't perform such optimizations. LLVM that's under LDC is
probably able to perform such optimizations, but in the language there is no
way to give such semantics to the compiler.
My suggestion for you is to ask for such feature in the main D newsgroup,
and/or in bugzilla. In the meantime you can also ask such feature to LDC
developers, they may just add a small LDC-specific pragma that gives such
semantics to the LLVM (in future, when D will add such annotation LDC
developers will just change the syntax of this feature). (I'll ask to LDC
developers to see what they think).

Bye,
bearophile

Stewart Gordon <smjg_1998 yahoo.com> writes:

#ponce wrote:
 I'm currently using a lot of pointers to perform heavy computation
 
 Has D the equivalent for C's restrict ? More generally, how does D 
 cope with the aliasing of pointers ? I think it's crucial for the 
 code optimizer.


My recollection of reading the spec is that a D compiler is allowed to 
optimise by assuming no pointer aliasing.  But I can't remember at the 
moment where I read this.

But in the absence of this, you can use contracts to guard against at 
least the simplest forms of aliasing.

Stewart.

#ponce <aliloko gmail.com> writes:

Stewart Gordon Wrote:
 My recollection of reading the spec is that a D compiler is allowed to 
 optimise by assuming no pointer aliasing.  But I can't remember at the 
 moment where I read this.


I don't know if this is neat or nasty for a compiler to do so. 

OT : Is there a DMD switch to disable bound check exceptions ? This way I
wouldn't have to rely on pointers so much.

#ponce <aliloko gmail.com> writes:

#ponce Wrote:

 Stewart Gordon Wrote:
 My recollection of reading the spec is that a D compiler is allowed to 
 optimise by assuming no pointer aliasing.  But I can't remember at the 
 moment where I read this.


 I don't know if this is neat or nasty for a compiler to do so. 
 
 OT : Is there a DMD switch to disable bound check exceptions ? This way I
wouldn't have to rely on pointers so much.

"Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> writes:

#ponce wrote:
 Stewart Gordon Wrote:
 My recollection of reading the spec is that a D compiler is allowed to 
 optimise by assuming no pointer aliasing.  But I can't remember at the 
 moment where I read this.


 I don't know if this is neat or nasty for a compiler to do so. 
 
 OT : Is there a DMD switch to disable bound check exceptions ? This way I
wouldn't have to rely on pointers so much.



The -release switch turns off array bounds checking. However, it also 
disables contracts and asserts.

-Lars

Stewart Gordon <smjg_1998 yahoo.com> writes:

#ponce wrote:
<snip>
 OT : Is there a DMD switch to disable bound check exceptions ? This way I
wouldn't have to rely on pointers so much.


Why do you want to do that?  Sounds like a case of trying to fix the 
wrong problem.

Stewart.

grauzone <none example.net> writes:

#ponce wrote:
 Stewart Gordon Wrote:
 My recollection of reading the spec is that a D compiler is allowed to 
 optimise by assuming no pointer aliasing.  But I can't remember at the 
 moment where I read this.


 I don't know if this is neat or nasty for a compiler to do so. 
 
 OT : Is there a DMD switch to disable bound check exceptions ? This way I
wouldn't have to rely on pointers so much.


If you always want DMD never to bounds check for specific code, you just 
can write "a.ptr[index]" instead of "a[index]" (when a is an array). 
That's because array.ptr returns a pointer to the first element, and 
using [] on a pointer works exactly like C pointer math. The good thing 
about this is that you still can use array slices and the .length field, 
so the code most likely is less messy than the C version would be.

#ponce <aliloko gmail.com> writes:

 If you always want DMD never to bounds check for specific code, you just 
 can write "a.ptr[index]" instead of "a[index]" (when a is an array). 
 That's because array.ptr returns a pointer to the first element, and 
 using [] on a pointer works exactly like C pointer math. The good thing 
 about this is that you still can use array slices and the .length field, 
 so the code most likely is less messy than the C version would be.


Interesting tip, thanks !