DmdAnal: Turn `LP(A)` into `LP(L)` in signatures (#19407)wip/T19407

This patch fixes some abundant reboxing of `DynFlags` in
`GHC.HsToCore.Match.Literal.warnAboutOverflowedLit` with a justifiable hack.

See the new `Note [Turn LP(A) into LP(M) in signatures]` and the new regression
test `T19407`.

There is a +4% ghc/alloc metric increase in T12545. The baseline is 1.7GB, this
patch uses 1.76GB. But if I pass `-v` then suddenly the baseline takes 1.8GB, this
patch 1.78GB. So it's actually an improvement! It appears that this patch is
somehow a bit more strict. In fact, in other jobs the same metric decreases.
Tracked as #19801.

Metric Increase:
    T12545
Metric Decrease:
    T12545

9 files changed, 141 insertions, 41 deletions

diff --git a/compiler/GHC/Types/Demand.hs b/compiler/GHC/Types/Demand.hs
index c4e25a1a47..2dc89cb175 100644
--- a/compiler/GHC/Types/Demand.hs
+++ b/compiler/GHC/Types/Demand.hs
@@ -716,7 +716,7 @@ These two SubDemands:
 are semantically equivalent, but we do not turn the former into
 the latter, for a regrettable-subtle reason.  Consider
   f p1@(x,y) = (y,x)
-  g h p2@(_,_) = h p
+  g h p2@(_,_) = h p2
 We want to unbox @p1@ of @f@, but not @p2@ of @g@, because @g@ only uses
 @p2@ boxed and we'd have to rebox. So we give @p1@ demand LP(L,L) and @p2@
 demand @L@ to inform 'GHC.Core.Opt.WorkWrap.Utils.wantToUnboxArg', which will
@@ -729,7 +729,7 @@ little bit of boxity analysis.  Not very nice.
 Note [L should win]
 ~~~~~~~~~~~~~~~~~~~
 Both in 'lubSubDmd' and 'plusSubDmd' we want @L `plusSubDmd` LP(..))@ to be @L@.
-Why?  Because U carries the implication the whole thing is used, box and all,
+Why?  Because L carries the implication the whole thing is used, box and all,
 so we don't want to w/w it, cf. Note [Don't optimise LP(L,L,...) to L].
 If we use it both boxed and unboxed, then we are definitely using the box,
 and so we are quite likely to pay a reboxing cost. So we make U win here.
@@ -751,6 +751,31 @@ Compare with: (C) making L win for plus, but LP(..) win for lub
             Max          +0.1%     +1.0%    +21.0%    +21.0%     +0.5%
  Geometric Mean          +0.0%     +0.0%     -0.0%     -0.1%     -0.1%
 
+Note [Turn LP(A) into LP(M) in signatures]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider T19407:
+
+  data Huge = Huge Bool () ... () -- think: DynFlags
+  data T = T { h :: Huge, n :: Int }
+  f t@(T h _) = g h t
+  g (H b _ ... _) t = if b then 1 else n t
+
+The body of `g` puts (approx.) demand `LP(A,1)` on `t`. But we better not put
+that demand in `g`'s signature! If we do, then `f` puts demand
+`SP(1P(1L,A,..),ML)` on `t` and we get
+
+  f (T (H b _ ... _) n) = $wf b n
+  $wf b n = $wg b (T (H b x ... x) n)
+  $wg = ...
+
+Massive reboxing in `$wf`! Solution: The signature of `g` should better say
+`LP(M,1)`, then `f`'s signature says `SP(1P(1L,M,..),ML)` and `h` will not be
+reboxed because passing all fields of `h` to `$wf` would run beyond the arg
+limit in W/W. Which in turn means that `f` will not be W/W'd *at all*!
+So this solution is quite unsatisfying as then `f`'s signature lies, probably
+incurring reboxing at its call sites... I can think of no fix other than a =
+proper boxity analysis.
+
 Note [Computing one-shot info]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Consider a call
@@ -1436,11 +1461,25 @@ newtype DmdSig
   deriving Eq
 
 -- | Turns a 'DmdType' computed for the particular 'Arity' into a 'DmdSig'
--- unleashable at that arity. See Note [Understanding DmdType and DmdSig]
+-- unleashable at that arity. See Note [Understanding DmdType and DmdSig].
 mkDmdSigForArity :: Arity -> DmdType -> DmdSig
 mkDmdSigForArity arity dmd_ty@(DmdType fvs args div)
-  | arity < dmdTypeDepth dmd_ty = DmdSig (DmdType fvs (take arity args) div)
-  | otherwise                   = DmdSig (etaExpandDmdType arity dmd_ty)
+  | arity < dmdTypeDepth dmd_ty = DmdSig dmd_ty'
+  | otherwise                   = DmdSig (etaExpandDmdType arity dmd_ty')
+  where
+    -- See Note [Turn LP(A) into LP(M) in signatures]
+    args' = map forgetAbsentInLazyProd args
+    !dmd_ty' = DmdType fvs (take arity args') div
+
+forgetAbsentInLazyProd :: Demand -> Demand
+forgetAbsentInLazyProd (n :* Prod ds)
+  | isStrict n = n :* Prod (map forgetAbsentInLazyProd ds)
+  | otherwise  = n :* Prod (map abs_to_once ds)
+  where
+    abs_to_once d@(n :* _)
+      | isAbs n   = polyDmd C_01
+      | otherwise = d
+forgetAbsentInLazyProd d  = d
 
 mkClosedDmdSig :: [Demand] -> Divergence -> DmdSig
 mkClosedDmdSig ds res = mkDmdSigForArity (length ds) (DmdType emptyDmdEnv ds res)
diff --git a/testsuite/tests/arityanal/should_compile/Arity11.stderr b/testsuite/tests/arityanal/should_compile/Arity11.stderr
index 92c7649dd2..6581192225 100644
--- a/testsuite/tests/arityanal/should_compile/Arity11.stderr
+++ b/testsuite/tests/arityanal/should_compile/Arity11.stderr
@@ -1,6 +1,6 @@
 
 ==================== Tidy Core ====================
-Result size of Tidy Core = {terms: 129, types: 94, coercions: 0, joins: 0/5}
+Result size of Tidy Core = {terms: 129, types: 98, coercions: 0, joins: 0/5}
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 F11.fib1 :: Integer
@@ -33,50 +33,50 @@ F11.f11_fib
       }
 end Rec }
 
--- RHS size: {terms: 52, types: 26, coercions: 0, joins: 0/5}
-F11.$wfib [InlPrag=[2]] :: forall {a1} {a2}. (a1 -> a1 -> Bool) -> (Num a1, Num a2) => a1 -> a2
-[GblId, Arity=4, Str=<SCS(C1(L))><LP(A,LCL(C1(L)),A,A,A,A,L)><LP(LCL(C1(L)),A,A,A,A,A,MCM(L))><L>, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 150 60 0] 460 0}]
+-- RHS size: {terms: 52, types: 27, coercions: 0, joins: 0/5}
+F11.$wfib [InlPrag=[2]] :: forall {t} {a}. (t -> t -> Bool) -> (Num t, Num a) => t -> a
+[GblId, Arity=4, Str=<SCS(C1(L))><LP(M,LCL(C1(L)),M,M,M,M,L)><LP(LCL(C1(L)),M,M,M,M,M,MCM(L))><L>, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 150 60 0] 460 0}]
 F11.$wfib
-  = \ (@a) (@a1) (ww :: a -> a -> Bool) (w :: Num a) (w1 :: Num a1) (w2 :: a) ->
+  = \ (@t) (@a) (ww :: t -> t -> Bool) (w :: Num t) (w1 :: Num a) (w2 :: t) ->
       let {
-        lvl :: a
+        lvl :: t
         [LclId]
-        lvl = fromInteger @a w F11.fib3 } in
+        lvl = fromInteger @t w F11.fib3 } in
       let {
-        lvl1 :: a
+        lvl1 :: t
         [LclId]
-        lvl1 = fromInteger @a w F11.fib2 } in
+        lvl1 = fromInteger @t w F11.fib2 } in
       let {
-        lvl2 :: a1
+        lvl2 :: a
         [LclId]
-        lvl2 = fromInteger @a1 w1 F11.fib3 } in
+        lvl2 = fromInteger @a w1 F11.fib3 } in
       let {
-        lvl3 :: a
+        lvl3 :: t
         [LclId]
-        lvl3 = fromInteger @a w F11.fib1 } in
+        lvl3 = fromInteger @t w F11.fib1 } in
       letrec {
-        fib4 [Occ=LoopBreaker, Dmd=SCS(L)] :: a -> a1
+        fib4 [Occ=LoopBreaker, Dmd=SCS(L)] :: t -> a
         [LclId, Arity=1, Str=<L>, Unf=OtherCon []]
         fib4
-          = \ (ds :: a) ->
+          = \ (ds :: t) ->
               case ww ds lvl3 of {
                 False ->
                   case ww ds lvl of {
-                    False -> + @a1 w1 (fib4 (- @a w ds lvl)) (fib4 (- @a w ds lvl1));
+                    False -> + @a w1 (fib4 (- @t w ds lvl)) (fib4 (- @t w ds lvl1));
                     True -> lvl2
                   };
                 True -> lvl2
               }; } in
       fib4 w2
 
--- RHS size: {terms: 14, types: 19, coercions: 0, joins: 0/0}
-fib [InlPrag=[2]] :: forall {a1} {a2}. (Eq a1, Num a1, Num a2) => a1 -> a2
+-- RHS size: {terms: 14, types: 20, coercions: 0, joins: 0/0}
+fib [InlPrag=[2]] :: forall {t} {a}. (Eq t, Num t, Num a) => t -> a
 [GblId,
  Arity=4,
- Str=<1P(SCS(C1(L)),A)><LP(A,LCL(C1(L)),A,A,A,A,L)><LP(LCL(C1(L)),A,A,A,A,A,L)><L>,
+ Str=<1P(SCS(C1(L)),A)><LP(L,LCL(C1(L)),L,L,L,L,L)><LP(LCL(C1(L)),L,L,L,L,L,L)><L>,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=4,unsat_ok=True,boring_ok=False)
-         Tmpl= \ (@a) (@a1) (w [Occ=Once1!] :: Eq a) (w1 [Occ=Once1] :: Num a) (w2 [Occ=Once1] :: Num a1) (w3 [Occ=Once1] :: a) -> case w of { GHC.Classes.C:Eq ww1 [Occ=Once1] _ [Occ=Dead] -> F11.$wfib @a @a1 ww1 w1 w2 w3 }}]
-fib = \ (@a) (@a1) (w :: Eq a) (w1 :: Num a) (w2 :: Num a1) (w3 :: a) -> case w of { GHC.Classes.C:Eq ww1 ww2 -> F11.$wfib @a @a1 ww1 w1 w2 w3 }
+         Tmpl= \ (@t) (@a) (w [Occ=Once1!] :: Eq t) (w1 [Occ=Once1] :: Num t) (w2 [Occ=Once1] :: Num a) (w3 [Occ=Once1] :: t) -> case w of { GHC.Classes.C:Eq ww [Occ=Once1] _ [Occ=Dead] -> F11.$wfib @t @a ww w1 w2 w3 }}]
+fib = \ (@t) (@a) (w :: Eq t) (w1 :: Num t) (w2 :: Num a) (w3 :: t) -> case w of { GHC.Classes.C:Eq ww ww1 -> F11.$wfib @t @a ww w1 w2 w3 }
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 F11.f3 :: Integer
diff --git a/testsuite/tests/arityanal/should_compile/Arity14.stderr b/testsuite/tests/arityanal/should_compile/Arity14.stderr
index d2a9716d04..5a395e1343 100644
--- a/testsuite/tests/arityanal/should_compile/Arity14.stderr
+++ b/testsuite/tests/arityanal/should_compile/Arity14.stderr
@@ -1,8 +1,8 @@
 
 ==================== Tidy Core ====================
-Result size of Tidy Core = {terms: 56, types: 81, coercions: 0, joins: 0/3}
+Result size of Tidy Core = {terms: 56, types: 87, coercions: 0, joins: 0/3}
 
--- RHS size: {terms: 3, types: 2, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 3, types: 3, coercions: 0, joins: 0/0}
 F14.f1 :: forall {t}. t -> t
 [GblId,
  Arity=1,
@@ -16,9 +16,9 @@ F14.f2 :: Integer
 [GblId, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 100 0}]
 F14.f2 = 1
 
--- RHS size: {terms: 35, types: 23, coercions: 0, joins: 0/3}
+-- RHS size: {terms: 35, types: 24, coercions: 0, joins: 0/3}
 F14.$wf14 [InlPrag=[2]] :: forall {t}. (t -> t -> Bool) -> Num t => t -> t -> t -> t
-[GblId, Arity=4, Str=<SCS(C1(L))><LP(LCL(C1(L)),A,A,A,A,A,MCM(L))><L><L>, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 90 0 0] 300 0}]
+[GblId, Arity=4, Str=<SCS(C1(L))><LP(LCL(C1(L)),M,M,M,M,M,MCM(L))><L><L>, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 90 0 0] 300 0}]
 F14.$wf14
   = \ (@t) (ww :: t -> t -> Bool) (w :: Num t) (w1 :: t) (w2 :: t) ->
       let {
@@ -41,14 +41,14 @@ F14.$wf14
               }; } in
       f3 w1 w2
 
--- RHS size: {terms: 13, types: 33, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 13, types: 34, coercions: 0, joins: 0/0}
 f14 [InlPrag=[2]] :: forall {t}. (Ord t, Num t) => t -> t -> t -> t
 [GblId,
  Arity=4,
- Str=<1P(A,A,SCS(C1(L)),A,A,A,A,A)><LP(LCL(C1(L)),A,A,A,A,A,L)><L><L>,
+ Str=<1P(A,A,SCS(C1(L)),A,A,A,A,A)><LP(LCL(C1(L)),L,L,L,L,L,L)><L><L>,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=4,unsat_ok=True,boring_ok=False)
-         Tmpl= \ (@t) (w [Occ=Once1!] :: Ord t) (w1 [Occ=Once1] :: Num t) (w2 [Occ=Once1] :: t) (w3 [Occ=Once1] :: t) -> case w of { GHC.Classes.C:Ord _ [Occ=Dead] _ [Occ=Dead] ww3 [Occ=Once1] _ [Occ=Dead] _ [Occ=Dead] _ [Occ=Dead] _ [Occ=Dead] _ [Occ=Dead] -> F14.$wf14 @t ww3 w1 w2 w3 }}]
-f14 = \ (@t) (w :: Ord t) (w1 :: Num t) (w2 :: t) (w3 :: t) -> case w of { GHC.Classes.C:Ord ww1 ww2 ww3 ww4 ww5 ww6 ww7 ww8 -> F14.$wf14 @t ww3 w1 w2 w3 }
+         Tmpl= \ (@t) (w [Occ=Once1!] :: Ord t) (w1 [Occ=Once1] :: Num t) (w2 [Occ=Once1] :: t) (w3 [Occ=Once1] :: t) -> case w of { GHC.Classes.C:Ord _ [Occ=Dead] _ [Occ=Dead] ww2 [Occ=Once1] _ [Occ=Dead] _ [Occ=Dead] _ [Occ=Dead] _ [Occ=Dead] _ [Occ=Dead] -> F14.$wf14 @t ww2 w1 w2 w3 }}]
+f14 = \ (@t) (w :: Ord t) (w1 :: Num t) (w2 :: t) (w3 :: t) -> case w of { GHC.Classes.C:Ord ww ww1 ww2 ww3 ww4 ww5 ww6 ww7 -> F14.$wf14 @t ww2 w1 w2 w3 }
 
 
 
diff --git a/testsuite/tests/simplCore/should_compile/T4908.stderr b/testsuite/tests/simplCore/should_compile/T4908.stderr
index f8f9107485..6002e010ac 100644
--- a/testsuite/tests/simplCore/should_compile/T4908.stderr
+++ b/testsuite/tests/simplCore/should_compile/T4908.stderr
@@ -59,7 +59,7 @@ end Rec }
 T4908.$wf [InlPrag=[2]] :: Int# -> (Int, Int) -> Bool
 [GblId,
  Arity=2,
- Str=<1L><MP(A,MP(ML))>,
+ Str=<1L><MP(M,MP(ML))>,
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True, Guidance=IF_ARGS [30 20] 101 20}]
 T4908.$wf
@@ -81,7 +81,7 @@ T4908.$wf
 f [InlPrag=[2]] :: Int -> (Int, Int) -> Bool
 [GblId,
  Arity=2,
- Str=<1P(1L)><MP(A,MP(ML))>,
+ Str=<1P(1L)><MP(M,MP(ML))>,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=2,unsat_ok=True,boring_ok=False)
diff --git a/testsuite/tests/stranal/should_compile/T10694.stderr b/testsuite/tests/stranal/should_compile/T10694.stderr
index 481c350fc2..a0891f8100 100644
--- a/testsuite/tests/stranal/should_compile/T10694.stderr
+++ b/testsuite/tests/stranal/should_compile/T10694.stderr
@@ -34,8 +34,8 @@ pm [InlPrag=[final]] :: Int -> Int -> (Int, Int)
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=2,unsat_ok=True,boring_ok=False)
          Tmpl= \ (w [Occ=Once1] :: Int) (w1 [Occ=Once1] :: Int) ->
-                 case T10694.$wpm w w1 of { (# ww1 [Occ=Once1], ww2 [Occ=Once1] #) -> (ww1, ww2) }}]
-pm = \ (w :: Int) (w1 :: Int) -> case T10694.$wpm w w1 of { (# ww1, ww2 #) -> (ww1, ww2) }
+                 case T10694.$wpm w w1 of { (# ww [Occ=Once1], ww1 [Occ=Once1] #) -> (ww, ww1) }}]
+pm = \ (w :: Int) (w1 :: Int) -> case T10694.$wpm w w1 of { (# ww, ww1 #) -> (ww, ww1) }
 
 -- RHS size: {terms: 8, types: 9, coercions: 0, joins: 0/0}
 m :: Int -> Int -> Int
@@ -45,7 +45,7 @@ m :: Int -> Int -> Int
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=2,unsat_ok=True,boring_ok=False)
          Tmpl= \ (x [Occ=Once1] :: Int) (y [Occ=Once1] :: Int) -> case pm x y of { (_ [Occ=Dead], mr [Occ=Once1]) -> mr }}]
-m = \ (x :: Int) (y :: Int) -> case T10694.$wpm x y of { (# ww1, ww2 #) -> ww2 }
+m = \ (x :: Int) (y :: Int) -> case T10694.$wpm x y of { (# ww, ww1 #) -> ww1 }
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 T10694.$trModule4 :: GHC.Prim.Addr#
diff --git a/testsuite/tests/stranal/sigs/T19407.hs b/testsuite/tests/stranal/sigs/T19407.hs
new file mode 100644
index 0000000000..af5eca8616
--- /dev/null
+++ b/testsuite/tests/stranal/sigs/T19407.hs
@@ -0,0 +1,21 @@
+{-# OPTIONS_GHC -O2 -fforce-recomp #-}
+
+-- | The gist here: `f` is strict in `t::T` and its field `h::Huge`, but mustn't unbox it.
+-- Otherwise, `$wf` has to rebox it for the call to `$wg` (which is lazy in `t`) and that
+-- also means reconstructing `h`, although most fields are absent anyway.
+--
+-- Solution: `g` is lazy in `t` and we can't unbox it. Thus, its signature
+-- shouldn't say which parts of `t` are absent!
+module T19407 where
+
+data Huge = Huge Bool () () () () () () () () () () () () () () () () () () () () ()
+data T = T { h :: Huge, n :: Int }
+
+f :: T -> Int -- like warnAboutOverflowedLit
+f t = g (h t) t
+{-# NOINLINE f #-}
+
+g :: Huge -> T -> Int -- like warnAboutOverflowedLiterals
+g (Huge b _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) t =
+  if b then 0 else n t
+{-# NOINLINE g #-}
diff --git a/testsuite/tests/stranal/sigs/T19407.stderr b/testsuite/tests/stranal/sigs/T19407.stderr
new file mode 100644
index 0000000000..7604ec039e
--- /dev/null
+++ b/testsuite/tests/stranal/sigs/T19407.stderr
@@ -0,0 +1,39 @@
+
+==================== Strictness signatures ====================
+T19407.$tc'Huge:
+T19407.$tc'T:
+T19407.$tcHuge:
+T19407.$tcT:
+T19407.$trModule:
+T19407.f: <SP(SP(SL,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M),ML)>
+T19407.g: <1P(1L,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A)><MP(M,ML)>
+T19407.h: <1P(1L,A)>
+T19407.n: <1P(A,1L)>
+
+
+
+==================== Cpr signatures ====================
+T19407.$tc'Huge:
+T19407.$tc'T:
+T19407.$tcHuge:
+T19407.$tcT:
+T19407.$trModule:
+T19407.f:
+T19407.g:
+T19407.h:
+T19407.n:
+
+
+
+==================== Strictness signatures ====================
+T19407.$tc'Huge:
+T19407.$tc'T:
+T19407.$tcHuge:
+T19407.$tcT:
+T19407.$trModule:
+T19407.f: <1P(SP(SL,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M),ML)>
+T19407.g: <1P(1L,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A)><MP(M,ML)>
+T19407.h: <1P(1L,A)>
+T19407.n: <1P(A,1L)>
+
+
diff --git a/testsuite/tests/stranal/sigs/T5075.stderr b/testsuite/tests/stranal/sigs/T5075.stderr
index e17d5e7c5c..e25bc744e9 100644
--- a/testsuite/tests/stranal/sigs/T5075.stderr
+++ b/testsuite/tests/stranal/sigs/T5075.stderr
@@ -1,7 +1,7 @@
 
 ==================== Strictness signatures ====================
 T5075.$trModule:
-T5075.loop: <SP(A,A,SCS(C1(L)),A,A,A,A,A)><LP(A,A,LCL(C1(L)),A,A,A,L)><L>
+T5075.loop: <SP(A,A,SCS(C1(L)),A,A,A,A,A)><LP(M,M,LCL(C1(L)),M,M,M,L)><L>
 
 
 
@@ -13,6 +13,6 @@ T5075.loop:
 
 ==================== Strictness signatures ====================
 T5075.$trModule:
-T5075.loop: <1P(A,A,SCS(C1(L)),A,A,A,A,A)><LP(A,A,LCL(C1(L)),A,A,A,L)><L>
+T5075.loop: <1P(A,A,SCS(C1(L)),A,A,A,A,A)><LP(L,L,LCL(C1(L)),L,L,L,L)><L>
 
 
diff --git a/testsuite/tests/stranal/sigs/all.T b/testsuite/tests/stranal/sigs/all.T
index 5d562a6a8c..39a70e3577 100644
--- a/testsuite/tests/stranal/sigs/all.T
+++ b/testsuite/tests/stranal/sigs/all.T
@@ -23,3 +23,4 @@ test('T13380c', expect_broken('!3014'), compile, [''])
 test('T13380f', normal, compile, [''])
 test('T18086', normal, compile, ['-package ghc'])
 test('T18957', normal, compile, [''])
+test('T19407', normal, compile, [''])