[OT] compiler optimisations

[Rikki Cattermole via Digitalmars-d]

On 23/04/2015 10:02 p.m., Andrea Fontana wrote:
> On Thursday, 23 April 2015 at 08:33:56 UTC, John Colvin wrote:
>> Why can no compiler I try optimise this toy example as I would expect?
>>
>> // uncomment if using a C compiler
>> // typedef unsigned int uint;
>> uint foo(uint a)
>> {
>>   if (a < 5)
>>     return (a * 3) / 3;
>>   else
>>     return 0;
>> }
>>
>> So, I would expect the compiler to be able to see that it is
>> equivalent to
>>
>> uint foo(uint a)
>> {
>>   return (a < 5) ? a : 0;
>> }
>>
>> But apparently not a single modern compiler I tried can do this
>> optimisation, unless it's hidden in some obscure flag I'm not aware of.
>>
>> An even more striking example can be found if you replace the / with
>> %, where the result of the function is then unconditionally zero, but
>> every compiler i tried still spat out multiplication instructions.
>>
>> Is there a good reason for this, or is it just " * and / aren't always
>> inverses, so never mind all the cases where they are"?
>>
>> Now I know that this seems like a unrealistic example, but when you're
>> in complicated meta-programming situations code like this can and will
>> appear.
>
> If I'm right, there's a website where I can see assembly generated by d
> compiler. And it's not dpaste... any hint?

asm.dlang.org