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The GHC compiler crashes on the following program.

module Test where

import Unsafe.Coerce
import Graphics.Rendering.OpenGL (color, Color3, GLdouble)

data D4 = D4 Double Double Double Double

crash :: D4 -> IO ()
crash c = color (invalidCast c)

invalidCast :: D4 -> Color3 GLdouble
invalidCast = unsafeCoerce

With the following output:

[1 of 1] Compiling Test             ( Test.hs, Test.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.6.1 for x86_64-apple-darwin):
	cgLookupPanic (probably invalid Core; try -dcore-lint)
    ww_s28U{v} [lid]
    static binds for:
    local binds for:

I've made several attempts to make the input program smaller, but all modifications will result in successful compilation.

The cast is invalid but should produce an runtime error, not a compile time error.

Changes I made that somehow prevent this bug from appearing:

• Changing the crash functions into point free style color . invalidCast.
• Decreasing the amount of doubles in the D4 datatype.
• Inlining the exact definitions from the OpenGL package.
• Using the print function instead of the color function.

(btw, I know I shouldn't use unsafeCoerce)

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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