Help optimizing code?

[Muld]

On Monday, 1 January 2018 at 16:47:40 UTC, Adam D. Ruppe wrote:
> On Monday, 1 January 2018 at 16:13:37 UTC, Muld wrote:
>> If you use .ptr then you get zero detection, even in debug 
>> builds.
>
> It is limited to the one expression where you wrote it, instead 
> of on the ENTIRE program like the build switches do.
>
> It is a lot easier to check correctness in an individual 
> expression than it is to check the entire program, including 
> stuff you didn't even realize might have been a problem.
>
> With the .ptr pattern, it is correct by default and you 
> individually change ones you (should) look carefully at. With 
> -boundscheck, it is wrong by default and most people don't even 
> look at it - people suggest it to newbies as an optimization 
> without mentioning how nasty it is.

It won't be just one line though. When you pretty much have to 
use it EVERYWHERE to get the optimization you want. It makes more 
sense to just turn off the check for the entire program and use 
your own asserts() where they are actually needed. That way you 
still get the checks in debug builds and have asserts where they 
are actually necessary.

>> I'd rather there be a potential bug than the program running 
>> to slow to be usable
>
> That's a ridiculous exaggeration. In this program, I saw a < 1% 
> time difference using those flags. -O -inline make a 50x bigger 
> difference!

Read the sentence right before this.. Jesus. People only read 
what they want.

>> or have zero debugging for indices in debug builds.
>
> You shouldn't be using .ptr until after you've carefully 
> checked and debugged the line of code where you are writing it. 
> That's the beauty of the pattern: it only affects one line of 
> code, so you can test it before you use it without affecting 
> the rest of the program.

It won't just be one line, and that's not beautiful. What happens 
when code gets refactored? You are constantly going to be 
flip-flopping the source code rather than a compiler flag or 
using multiple build configurations? How long are you even going 
to test for? The error that might happen for the code is probably 
difficult to detect, if it wasn't then having bounds checking at 
all wouldn't be necessary. Just test your code, that's the beauty 
of testing!