2 files changed, 21 insertions, 0 deletions
diff --git a/testsuite/tests/simplCore/should_compile/T20143.hs b/testsuite/tests/simplCore/should_compile/T20143.hs
new file mode 100644
index 0000000000..d85f173954
--- /dev/null
+++ b/testsuite/tests/simplCore/should_compile/T20143.hs
@@ -0,0 +1,20 @@
+{-# LANGUAGE ViewPatterns, GADTs #-}
+
+module T30243( getUL ) where
+
+import Data.Kind
+import Unsafe.Coerce
+
+newtype AsUnitLoop a (b :: Type) (c :: Type) = UnsafeUL a
+
+data SafeUnitLoop a b c where
+  SafeUnitLoop :: !a -> SafeUnitLoop a () ()
+
+mkSafeUnitLoop :: AsUnitLoop a b c -> SafeUnitLoop a b c
+mkSafeUnitLoop (UnsafeUL a) = unsafeCoerce (SafeUnitLoop a)
+
+getUL :: AsUnitLoop a b c -> a
+getUL (mkSafeUnitLoop -> SafeUnitLoop a) = a
+
+-- There should be no unsafeEqualityProof in the output
+-- when compiled with -O
diff --git a/testsuite/tests/simplCore/should_compile/all.T b/testsuite/tests/simplCore/should_compile/all.T
index 2fe050e1ba..616a469746 100644
--- a/testsuite/tests/simplCore/should_compile/all.T
+++ b/testsuite/tests/simplCore/should_compile/all.T
@@ -368,3 +368,4 @@ test('T19780', normal, compile, ['-O2'])
 test('T19794', normal, compile, ['-O'])
 test('T19890',  [ grep_errmsg(r'= T19890.foo1') ], compile, ['-O -ddump-simpl'])
 test('T20125',  [ grep_errmsg(r'= T20125.MkT') ], compile, ['-O -ddump-simpl -dsuppress-uniques'])
+test('T20143',  [ grep_errmsg(r'unsafeEqualityProof') ], compile, ['-O -ddump-simpl -dsuppress-uniques'])