Pointer aliasing in D (Was: Programming language benchmarks)

[Don]

Jens Mueller wrote:
> Andrei Alexandrescu wrote:
>> On 4/28/11 12:57 PM, Jens Mueller wrote:
>>> Walter Bright wrote:
>>>> On 4/28/2011 9:19 AM, Daniel Gibson wrote:
>>>>> But there's no need for a D compiler to optimize loops that just copy
>>>>> parts of an array into another array (and similar stuff), because in D
>>>>> you use slices for that - they're (probably) faster and easier to use.
>>>>> So IMHO it's fair to use slices where possible.
>>>>> (And they're a language feature and not just part of the library)
>>>>> Furthermore this particular benchmark is a "programming language
>>>>> benchmark" and not a compiler benchmark, so it's fair to use every
>>>>> feature of the language.
>>>>
>>>> For example, a lot of effort is expended in C and Fortran compilers
>>>> "reverse engineering" loops so they can be recompiled and optimized
>>>> as vector operations. I don't see ever bothering with this in D
>>>> compilers, as D offers a vector notation.
>>> If somebody wants to read the elaborate version of the above:
>>> http://drdobbs.com/blogs/229300270
>>> Walter's Dr. Dobb's articles are very good. I only read the new ones
>>> posted. But I have to read the older ones if I find some time.
>>> BTW
>>> In the book "Coder at Work" Fran Allen takes a quite strong position
>>> against C. She was deeply into Fortran compilers. She says: "We have
>>> seriously regressed, since C developed. C has destroyed our ability to
>>> advance the state of the art in automatic optimization, automatic
>>> parallelization, automatic mapping of a high-level language to the
>>> machine."
>>> When I read this some time ago I found that position quite interesting.
>>> But unfortunately I cannot tell how valid it is. Walter with all of his
>>> experience in developing compilers may give a well informed evaluation
>>> on Allen's statement. I'm just curious.
>>>
>>> Jens
>> It's simple - Fortran can assume that all data is unaliased
>> (although aliasing is still technically possible). C, with its
>> intensive pointer-based ethos that makes many aliasing-related
>> optimizations difficult, has annoyed many a Fortran aficionados.
> 
> Thanks. So if a compiler can assume that pointers do not alias it can
> generate much better code. What's D's standpoint on that matter then?
> C99 has restrict. I never came across something similar in D.
> 
> Jens

D reduces the use of pointers. You can do much more with arrays.