Align a variable on the stack.

[TheFlyingFiddle via Digitalmars-d-learn]

On Friday, 6 November 2015 at 11:38:29 UTC, Marc Schütz wrote:
> On Friday, 6 November 2015 at 11:37:22 UTC, Marc Schütz wrote:
>> Ok, benchA and benchB have the same assembler code generated. 
>> However, I _can_ reproduce the slowdown albeit on average only 
>> 20%-40%, not a factor of 10.
>
> Forgot to add that this is on Linux x86_64, so that probably 
> explains the difference.
>
>>
>> It turns out that it's always the first tested function that's 
>> slower. You can test this by switching benchA and benchB in 
>> the call to benchmark(). I suspect the reason is that the OS 
>> is paging in the code the first time, and we're actually 
>> seeing the cost of the page fault. If you a second round of 
>> benchmarks after the first one, that one shows more or less 
>> the same performance for both functions.

I tested swapping around the functions on windows x86 and I still 
get the same slowdown with the default initializer. Still 
basically the same running speed of both functions on windows 
x64. Interestingly enough the slowdown disappear if I add another 
float variable to the structs. This causes the assembly to change 
to using different instructions so I guess that is why. Also it 
only seems to affect small structs with floats in them. If I 
change the memebers to int both versions run at the same speed on 
x86 aswell.