Hi Guys,

There's a tool running the dmd testsuite.
called d_do_test.d

It uses so much memory during compilation that the "-lowmem" switch is mandatory and it uses about as much time to compile as does dmd itself.

Interestingly in the case the reason is actually legitimately CTFE.

My profiling tool pointed to a function called unifyNewLines as the main time taker.
This was actually wrong.
But the real time taker was not far from it.

string unifyDirSep(string str, string sep)

For demonstration purposes, and because I am lazy, I did a quick hack to remove the CTFE from it

---
string unifyDirSep(string str, string sep)
{
    version(ctfe)
    {
    static Regex!char re  = regex(`(?<=[-\w{}][-\w{}]*)/(?=[-\w][-\w/]*\.(di?|mixin)\b)`, "g");
    return std.regex.replace(str, re, sep);
    }
    else
    {
    static Regex!char* re;
    if (re is null)
        (*re) = regex(`(?<=[-\w{}][-\w{}]*)/(?=[-\w][-\w/]*\.(di?|mixin)\b)`, "g");
    return std.regex.replace(str, (*re), sep);
    }
}
---

Take this function; put it into a file and compile that file.
If your configuration is anything like mine that'll take around 2 seconds.
And it'll eat about 500 MB of ram
now compile that file with -version=ctfe
And you will see it taking 5 seconds and eating around 1.3GB of ram.

Cheers,

Stefan

P.S. Don't put your regex as initExp!

On Saturday, 6 June 2020 at 18:04:26 UTC, Stefan Koch wrote:

> And it'll eat about 500 MB of ram
> now compile that file with -version=ctfe
> And you will see it taking 5 seconds and eating around 1.3GB of ram.

All I can say is... ouch.