DmdAnal: Testcase about splitFVs and dmdFix abortion

Any variable with useful information (strict or used-once) will not be
included in lazy_fv (according to splitFVs). If we now also remove them
from the strictness signatures, their uses are not recorded anywhere –
and then probably considered absent.

2 files changed, 30 insertions, 0 deletions

diff --git a/testsuite/tests/stranal/should_run/T12368a.hs b/testsuite/tests/stranal/should_run/T12368a.hs
new file mode 100644
index 0000000000..301d044493
--- /dev/null
+++ b/testsuite/tests/stranal/should_run/T12368a.hs
@@ -0,0 +1,27 @@
+-- Needs to be a product type
+data Stream = S Int Stream
+
+-- a is wrongly recorded abstent if the non-lazy-fv from foo are thrown away.
+bar :: Int -> Int -> Stream -> Int
+bar a n s = foo n s
+  where
+    -- Non terminating local rec, strict in a
+    foo :: Int -> Stream -> Int
+    foo 0 (S n s) = a
+    foo i (S n s) = a `seq` n + foo (i-1) s
+{-# NOINLINE bar #-}
+
+
+baz :: Int -> Int -> Int
+baz 0 not_absent = 0
+baz 1 not_absent = baz 2 not_absent
+baz x not_absent = bar not_absent 1000 arg
+  where
+    arg = S 1 arg
+
+bamf x = baz x (error "This is good!")
+{-# NOINLINE bamf #-}
+
+
+main :: IO ()
+main = bamf 10 `seq` return ()
diff --git a/testsuite/tests/stranal/should_run/T12368a.stderr b/testsuite/tests/stranal/should_run/T12368a.stderr
new file mode 100644
index 0000000000..98246d33d0
--- /dev/null
+++ b/testsuite/tests/stranal/should_run/T12368a.stderr
@@ -0,0 +1,3 @@
+T12368a: This is good!
+CallStack (from HasCallStack):
+  error, called at T12368a.hs:22:17 in main:Main