Very slow compiling when computing big constant arrays

[tsoj]

The following example takes almost 4 minutes to compile on an i5-8250U.

Example

const size = 50_000

const stuff = block:
    var a: array[size, int]
    a

const zeugs = block:
    var zeugs: array[size, int]
    for i in 0..<size:
        zeugs[i] = stuff[i]
    zeugs

echo zeugs[0]

Current Output

$ time nim c --run main.nim
Hint: used config file '/home/tsoj/.choosenim/toolchains/nim-#devel/config/nim.cfg' [Conf]
Hint: used config file '/home/tsoj/.choosenim/toolchains/nim-#devel/config/config.nims' [Conf]
.........................................................
CC: stdlib_digitsutils.nim
CC: stdlib_assertions.nim
CC: stdlib_dollars.nim
CC: stdlib_io.nim
CC: stdlib_system.nim
CC: main.nim
Hint:  [Link]
Hint: gc: refc; opt: none (DEBUG BUILD, `-d:release` generates faster code)
26631 lines; 237.035s; 145.992MiB peakmem; proj: /home/tsoj/Dokumente/Projects/nim-slow-compile-test/main.nim; out: /home/tsoj/Dokumente/Projects/nim-slow-compile-test/main [SuccessX]
Hint: /home/tsoj/Dokumente/Projects/nim-slow-compile-test/main  [Exec]
0

________________________________________________________
Executed in  237.21 secs    fish           external
   usr time  236.79 secs    1.02 millis  236.79 secs
   sys time    0.23 secs    0.59 millis    0.23 secs

Expected Output

I would expect the compilation to take less time. The following example compiles in less than one second, despite having equally big constant arrays:

import random

const size = 50_000

const stuff = block:
    var a: array[size, int]
    a

const zeugs = block:
    var zeugs: array[size, int]
    for i in 0..<size:
        zeugs[i] = i
    zeugs

echo stuff[rand(0..<size)]
echo zeugs[rand(0..<size)]

Additional information

$ nim -v
Nim Compiler Version 1.7.1 [Linux: amd64]
Compiled at 2021-10-31
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 2bda4a30a6b12dd0840dc347e454e54fe26721e7
active boot switches: -d:release

[jackhftang]

Not a solution, but to mitigate the problem, move the const stuff outside for loop.

const size = 50_000

const stuff = block:
    var a: array[size, int]
    a

const zeugs = block:
    let inline = stuff
    var zeugs: array[size, int]
    for i in 0..<size:
        zeugs[i] = inline[i]
    zeugs

echo zeugs[1]