Re: pure functions/methods
Namespace:
So only GDC optimized "pure" functions at all?
I've seen DMD performs some optimizations with "strongly pure"
functions that return integral values.
If you have code like:
int sqr(in int x) pure nothrow { return x * x; }
int y = ...
auto r = sqr(y) + sqr(y);
I think DMD replaces that with this, even when inlining is
disabled:
int y = ...
auto r = sqr(y) * 2;
Bye,
bearophile
Re: pure functions/methods
On Friday, 20 April 2012 at 09:55:28 UTC, Timon Gehr wrote: On 04/20/2012 10:06 AM, Namespace wrote: The sense of pure functions isn't clear to me. What is the advantage of pure functions / methods? 1. It enables stateless reasoning about program parts. 2. It enables certain compiler optimizations. I inform the compiler with "const" that this method does not change the current object, and therefore he can optimize (at least in C++) this method. const on a method does not give any guarantees in C++. A C++ compiler cannot perform optimizations based on a const method. How and what optimized the compiler if i have "pure" or "const pure" functions / methods? DMD does not do a lot there currently. This article seems to discuss what GCC does with pure functions: http://lwn.net/Articles/285332/ So only GDC optimized "pure" functions at all?
Re: pure functions/methods
On 04/20/2012 10:06 AM, Namespace wrote: The sense of pure functions isn't clear to me. What is the advantage of pure functions / methods? 1. It enables stateless reasoning about program parts. 2. It enables certain compiler optimizations. I inform the compiler with "const" that this method does not change the current object, and therefore he can optimize (at least in C++) this method. const on a method does not give any guarantees in C++. A C++ compiler cannot perform optimizations based on a const method. How and what optimized the compiler if i have "pure" or "const pure" functions / methods? DMD does not do a lot there currently. This article seems to discuss what GCC does with pure functions: http://lwn.net/Articles/285332/
Re: pure functions/methods
On 4/20/2012 3:06 AM, Namespace wrote: The sense of pure functions isn't clear to me. What is the advantage of pure functions / methods? I inform the compiler with "const" that this method does not change the current object, and therefore he can optimize (at least in C++) this method. How and what optimized the compiler if i have "pure" or "const pure" functions / methods? Simplest explanation I can think of is: a const function of a class can't modify its own classes data a pure function can't modify any data, or call other functions that are not also pure (though there are exceptions)
Re: pure functions/methods
On 4/20/12 4:06 PM, Namespace wrote: The sense of pure functions isn't clear to me. What is the advantage of pure functions / methods? I inform the compiler with "const" that this method does not change the current object, and therefore he can optimize (at least in C++) this method. How and what optimized the compiler if i have "pure" or "const pure" functions / methods? As far as I know pure functions always return the same results given the same arguments. They also don't cause any side effect. http://en.wikipedia.org/wiki/Pure_function Many invocations of a pure function can be executed in parallel because they don't have side effects. There's also a chance of caching their result since it only depends on the value of their arguments (though I doubt what rule the compiler can use to decide to do it). I don't think any of the following benefits are implemented in DMD.
pure functions/methods
The sense of pure functions isn't clear to me. What is the advantage of pure functions / methods? I inform the compiler with "const" that this method does not change the current object, and therefore he can optimize (at least in C++) this method. How and what optimized the compiler if i have "pure" or "const pure" functions / methods?
