Internal Compiler Error Example #1

[tharnival]

With the files 1.fut (renamed because GitHub doesn't accept .fut):
1.txt
(At line 43 and 47 are some comments about the general location of the problem.)

And games.fut (again renamed):
games.txt

If I run the command "futhark opencl 1.fut" with Futhark 0.22.0, I get the error:

Internal compiler error.  Please report this:
  https://github.com/diku-dk/futhark/issues
After internalisation:
In function brute_force_8110
When checking function body
In expression of statement
  {brute_force_res_12160 : ({}, [1i64]f64),
   brute_force_res_12161 : ({}, i64)}
in true branch
In expression of statement
  {results_12239 : ({}, i64),
   results_12240 : ({}, i64),
   results_12241 : ({}, bool),
   results_12242 : ({}, [1i64][n₆_12163]i32),
   results_12243 : ({}, [1i64][n₆_12163]i32),
   results_12244 : ({}, [1i64][depth2_12148]i64),
   results_12245 : ({}, [1i64]i64),
   results_12246 : ({}, [1i64]bool),
   results_12247 : ({}, [1i64][n₆_12163]f64),
   results_12248 : ({}, [1i64][n₆_12163]f64),
   results_12249 : ({}, [1i64][n₆_12163]f64),
   results_12250 : ({}, [1i64]i64),
   results_12251 : ({states_12183, states_12184, states_12185, states_12186,
                     states_12187, states_12188, states_12189, states_12190,
                     states_12191, loop_init_12192}, [results_12239]i64),
   results_12252 : ({loop_init_12193}, [results_12240]i64)}
Type error:
Variable states_12174 referenced after being consumed.

[athas]

I think this program is wrong and shouldn't pass the type checker. Here is a simpler example of what is happening:

def main [n] (xs: *[n](i32,i32)) =
  let f i = let (a,_) = xs[i] in a
  in loop xs for i < n do xs with [i] = (f i, f i)

A local function is closing over a variable that is consumed later, yet we can still apply that function. We do track aliases of functions for just this reason, but there must be a bug somewhere.