What LDC flags should be used to get the fastest executable on Windows?

[Dennis]

On Saturday, 6 March 2021 at 10:57:31 UTC, Preetpal wrote:
> On Saturday, 6 March 2021 at 10:51:35 UTC, Preetpal wrote:
>> On Saturday, 6 March 2021 at 09:07:05 UTC, Imperatorn wrote:
>>> There's not much going on in the code there. Where are you 
>>> experiencing problems? Have you profiled it?
>>
>> As it is small program, I re-implemented it in C 
>> (https://gist.github.com/preetpalS/81405cd78ade738034cfa6d49e2a4202) to see if it could reduce the problem I was seeing. Based on my observations it did reduce the problem but it did not eliminate it. This led me to believe that the issue I was seeing in the D version was performance-related.
>
> I just really want to be sure that the D version of the program 
> can match the C version of the program.

I very much doubt this is performance related.
Your program doesn't do any heavy computations itself, it just 
calls into the Windows API, which is dynamically linked, so 
link-time optimization makes no difference. Optimization flags 
like -O3 just shave off nanoseconds from the calling code.

A notable difference with your C version is that you use global 
variables, which in D are thread-local by default. To match C, 
make your declarations __gshared and see if it helps:

```
__gshared bool altPressed = false;
__gshared bool controlPressed = false;
__gshared bool shiftPressed = false;
__gshared bool winkeyPressed = false;
```