Incredible memory consumption for function with huge body

[dlangBugzillaToGithub]

kinke reported this on 2019-03-16T15:05:13Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19745

CC List

• Iain Buclaw (@ibuclaw)
• Puneet Goel

Description

void write(int a) {}

void main()
{
    int a;
    static foreach (i; 1 .. 400_000)
    {
        a = i;
        write(a);
    }
}

On my box with a 64-bit LDC, the process dies due to OOM after some 18 GB. 32-bit DMD dies much sooner obviously. From https://forum.dlang.org/post/nlhybmioaoxkydicmtjj@forum.dlang.org.

!!!There are attachements in the bugzilla issue that have not been copied over!!!

[dlangBugzillaToGithub]

puneet commented on 2019-03-16T17:50:19Z

Created attachment 1735
Code with a BIG function body

[dlangBugzillaToGithub]

puneet commented on 2019-03-16T17:54:28Z

With the static foreach, it seems it is the static foreach unrolling which takes a lot of memory.

On the other hand, if you create physical code with a large function, the compiler does not go OOM, but seems to take forever. On my i7 linux box I kill the compilation process after it failed to produce object file even after 2 hours compiler.

I have attached test.d.xz

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kinke commented on 2019-03-16T20:39:07Z

Ah, thanks for checking - then we have 2 separate, orthogonal issues here.

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ibuclaw (@ibuclaw) commented on 2019-03-21T07:51:10Z

This is a duplicate of another bug I think.

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ibuclaw (@ibuclaw) commented on 2019-03-21T07:55:44Z

(In reply to Puneet Goel from comment #2)
> With the static foreach, it seems it is the static foreach unrolling which
> takes a lot of memory.
> 
> On the other hand, if you create physical code with a large function, the
> compiler does not go OOM, but seems to take forever. On my i7 linux box I
> kill the compilation process after it failed to produce object file even
> after 2 hours compiler.
> 
> I have attached test.d.xz

What you are describing I think is covered by this bug.

https://issues.dlang.org/show_bug.cgi?id=6401

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dfj1esp02 commented on 2019-03-21T15:52:17Z

6401 is dmc backend optimizer problem, this example fails in frontend.