Memory usage exploding for complex pattern matching

[Ben Gamari]

"Victor Miraldo (UU)" <v.cacciarimiraldo at uu.nl> writes:

> Hello,
>
>>>>> I have just tried compiling my code with 8.4.2 and using
>>>>> -fmax-pmcheck-iterations=0,
>>>>> I gave GHC 12GB of ram and it still ran out (through `ulimit
>>>>> -v$((1024*1024*12))`).
>>>>>
>>>> Hmmm, I'm a bit confused. Why are our results so different? How
>>>> precisely are you invoking GHC?
>>>
>>> Here I meant my whole code, not just the repro. I could have been more clear.
>>> Nevertheless, I'm calling it through stack:
>>>
>> I'll admit that I am a bit lost; Minimal.hs compiles for me with a
>> maximum residency of ~3.5 GBytes with both -O1 and the PM check enabled
>> using GHC 8.4.1. Is this not the repro you are referring to?
>
> I get the same behavior as you for Minimal.hs.
>
> The "my code" above referred to the whole library that I'm developping.
> In fact, the Minimal.hs file contains a distilled version of that library with
> a template haskell splice that we are trying to use in one of our
> fully fledged examples.
>
Okay, I just wanted to be certain we were indeed seeing the same
behavior. Indeed 3.5 GB is quite a lot of memory for a 700 LoC program,
even one with the deep matches seen in Minimal.hs.

Cheers,

- Ben

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