Add a test for returning memory to the OS

testsuite/tests/ghc-regress/rts/all.T

@@ -91,3 +91,5 @@ test('exec_signals', [
      cmd_prefix('$MAKE exec_signals-prep && ./exec_signals_prepare'),
      extra_clean(['exec_signals_child', 'exec_signals_prepare'])
     ], compile_and_run, [''])
+
+test('return_mem_to_os', normal, compile_and_run, [''])

testsuite/tests/ghc-regress/rts/return_mem_to_os.hs

+
+import Control.Concurrent
+import System.IO
+import System.Mem
+
+main :: IO ()
+main = do hSetBuffering stdout LineBuffering
+          mapM_ doIter [1..3]
+
+doIter :: Int -> IO ()
+doIter n = do putStrLn ("Iteration " ++ show n)
+              let xs = [n .. 1000000 + n]
+              putStrLn ("Last: " ++ show (last xs))
+              putStrLn "GC 1 start"
+              performGC
+              putStrLn "GC 1 done"
+              putStrLn ("Head: " ++ show (head xs))
+              putStrLn "GC 2 start"
+              performGC
+              putStrLn "GC 2 done"
+

testsuite/tests/ghc-regress/rts/return_mem_to_os.stdout

+Iteration 1
+Last: 1000001
+GC 1 start
+GC 1 done
+Head: 1
+GC 2 start
+GC 2 done
+Iteration 2
+Last: 1000002
+GC 1 start
+GC 1 done
+Head: 2
+GC 2 start
+GC 2 done
+Iteration 3
+Last: 1000003
+GC 1 start
+GC 1 done
+Head: 3
+GC 2 start
+GC 2 done