WorkWrap: Remove mkWWargs (#19874)

`mkWWargs`'s job was pushing casts inwards and doing eta expansion to match
the arity with the number of argument demands we w/w for.

Nowadays, we use the Simplifier to eta expand to arity. In fact, in recent years
we have even seen the eta expansion done by w/w as harmful, see Note [Don't eta
expand in w/w]. If a function hasn't enough manifest lambdas, don't w/w it!

What purpose does `mkWWargs` serve in this world? Not a great one, it turns out!
I could remove it by pulling some important bits,
notably Note [Freshen WW arguments] and Note [Join points and beta-redexes].
Result: We reuse the freshened binder names of the wrapper in the
worker where possible (see testuite changes), much nicer!

In order to avoid scoping errors due to lambda-bound unfoldings in worker
arguments, we zap those unfoldings now. In doing so, we fix #19766.

Fixes #19874.

14 files changed, 73 insertions, 53 deletions

diff --git a/testsuite/tests/simplCore/should_compile/T13143.stderr b/testsuite/tests/simplCore/should_compile/T13143.stderr
index 87fbdd6213..c4c2db7462 100644
--- a/testsuite/tests/simplCore/should_compile/T13143.stderr
+++ b/testsuite/tests/simplCore/should_compile/T13143.stderr
@@ -70,15 +70,15 @@ T13143.$wg [InlPrag=[2], Occ=LoopBreaker]
   :: Bool -> Bool -> GHC.Prim.Int# -> GHC.Prim.Int#
 [GblId, Arity=3, Str=<1L><1L><L>, Unf=OtherCon []]
 T13143.$wg
-  = \ (w :: Bool) (w1 :: Bool) (ww :: GHC.Prim.Int#) ->
-      case w of {
+  = \ (ds :: Bool) (ds1 :: Bool) (ww :: GHC.Prim.Int#) ->
+      case ds of {
         False ->
-          case w1 of {
+          case ds1 of {
             False -> T13143.$wg GHC.Types.False GHC.Types.True ww;
             True -> GHC.Prim.+# ww 1#
           };
         True ->
-          case w1 of {
+          case ds1 of {
             False -> T13143.$wg GHC.Types.True GHC.Types.True ww;
             True -> case lvl of wild2 { }
           }
@@ -94,17 +94,17 @@ g [InlPrag=[2]] :: Bool -> Bool -> Int -> Int
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=3,unsat_ok=True,boring_ok=False)
-         Tmpl= \ (w [Occ=Once1] :: Bool)
-                 (w1 [Occ=Once1] :: Bool)
-                 (w2 [Occ=Once1!] :: Int) ->
-                 case w2 of { GHC.Types.I# ww [Occ=Once1] ->
-                 case T13143.$wg w w1 ww of ww1 [Occ=Once1] { __DEFAULT ->
+         Tmpl= \ (ds [Occ=Once1] :: Bool)
+                 (ds1 [Occ=Once1] :: Bool)
+                 (p [Occ=Once1!] :: Int) ->
+                 case p of { GHC.Types.I# ww [Occ=Once1] ->
+                 case T13143.$wg ds ds1 ww of ww1 [Occ=Once1] { __DEFAULT ->
                  GHC.Types.I# ww1
                  }
                  }}]
-g = \ (w :: Bool) (w1 :: Bool) (w2 :: Int) ->
-      case w2 of { GHC.Types.I# ww ->
-      case T13143.$wg w w1 ww of ww1 { __DEFAULT -> GHC.Types.I# ww1 }
+g = \ (ds :: Bool) (ds1 :: Bool) (p :: Int) ->
+      case p of { GHC.Types.I# ww ->
+      case T13143.$wg ds ds1 ww of ww1 { __DEFAULT -> GHC.Types.I# ww1 }
       }
 
 
diff --git a/testsuite/tests/simplCore/should_compile/T15631.stdout b/testsuite/tests/simplCore/should_compile/T15631.stdout
index e9e6a2bcab..ab181b58ed 100644
--- a/testsuite/tests/simplCore/should_compile/T15631.stdout
+++ b/testsuite/tests/simplCore/should_compile/T15631.stdout
@@ -1,7 +1,7 @@
       case GHC.List.$wlenAcc
-      case GHC.List.$wlenAcc @a w 0# of ww1 { __DEFAULT ->
-      case GHC.List.reverse1 @a w (GHC.Types.[] @a) of {
+      case GHC.List.$wlenAcc @a xs 0# of ww1 { __DEFAULT ->
+      case GHC.List.reverse1 @a xs (GHC.Types.[] @a) of {
         [] -> case Foo.f1 @a of { GHC.Types.I# v1 -> GHC.Prim.+# ww1 v1 };
           case GHC.List.$wlenAcc
-                 case Foo.$wf @a w of ww [Occ=Once1] { __DEFAULT ->
-      case Foo.$wf @a w of ww { __DEFAULT -> GHC.Types.I# ww }
+                 case Foo.$wf @a xs of ww [Occ=Once1] { __DEFAULT ->
+      case Foo.$wf @a xs of ww { __DEFAULT -> GHC.Types.I# ww }
diff --git a/testsuite/tests/simplCore/should_compile/T18013.stderr b/testsuite/tests/simplCore/should_compile/T18013.stderr
index 45f9900830..5c82b03c93 100644
--- a/testsuite/tests/simplCore/should_compile/T18013.stderr
+++ b/testsuite/tests/simplCore/should_compile/T18013.stderr
@@ -140,8 +140,8 @@ mapMaybeRule [InlPrag=[2]]
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=False)
-         Tmpl= \ (@a) (@b) (w [Occ=Once1!] :: Rule IO a b) ->
-                 case w of { Rule @s ww ww1 [Occ=OnceL1!] ->
+         Tmpl= \ (@a) (@b) (f [Occ=Once1!] :: Rule IO a b) ->
+                 case f of { Rule @s ww ww1 [Occ=OnceL1!] ->
                  T18013a.Rule
                    @IO
                    @(Maybe a)
@@ -176,8 +176,8 @@ mapMaybeRule [InlPrag=[2]]
                                       ~R# (s -> Maybe a -> IO (Result s (Maybe b))))
                  }}]
 mapMaybeRule
-  = \ (@a) (@b) (w :: Rule IO a b) ->
-      case w of { Rule @s ww ww1 ->
+  = \ (@a) (@b) (f :: Rule IO a b) ->
+      case f of { Rule @s ww ww1 ->
       let {
         lvl :: Result s (Maybe b)
         [LclId, Unf=OtherCon []]
diff --git a/testsuite/tests/simplCore/should_compile/T19246.stderr b/testsuite/tests/simplCore/should_compile/T19246.stderr
index 0c7894e56d..acfe1500b8 100644
--- a/testsuite/tests/simplCore/should_compile/T19246.stderr
+++ b/testsuite/tests/simplCore/should_compile/T19246.stderr
@@ -6,6 +6,6 @@
 ==================== Tidy Core rules ====================
 "SPEC f" [2] forall ($dOrd :: Ord Int). f @Int $dOrd = $sf
 "SPEC/T19246 $wf @Int" [2]
-    forall (w :: Ord Int). $wf @Int w = $s$wf
+    forall ($dOrd :: Ord Int). $wf @Int $dOrd = $s$wf
 
 
diff --git a/testsuite/tests/simplCore/should_compile/T3717.stderr b/testsuite/tests/simplCore/should_compile/T3717.stderr
index 6e8fe19294..bd6417b729 100644
--- a/testsuite/tests/simplCore/should_compile/T3717.stderr
+++ b/testsuite/tests/simplCore/should_compile/T3717.stderr
@@ -61,15 +61,15 @@ foo [InlPrag=[2]] :: Int -> Int
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=False)
-         Tmpl= \ (w [Occ=Once1!] :: Int) ->
-                 case w of { GHC.Types.I# ww [Occ=Once1] ->
+         Tmpl= \ (ds [Occ=Once1!] :: Int) ->
+                 case ds of { GHC.Types.I# ww [Occ=Once1] ->
                  case T3717.$wfoo ww of ww1 [Occ=Once1] { __DEFAULT ->
                  GHC.Types.I# ww1
                  }
                  }}]
 foo
-  = \ (w :: Int) ->
-      case w of { GHC.Types.I# ww ->
+  = \ (ds :: Int) ->
+      case ds of { GHC.Types.I# ww ->
       case T3717.$wfoo ww of ww1 { __DEFAULT -> GHC.Types.I# ww1 }
       }
 
diff --git a/testsuite/tests/simplCore/should_compile/T3772.stdout b/testsuite/tests/simplCore/should_compile/T3772.stdout
index 5ead45f9c3..abf4b8db14 100644
--- a/testsuite/tests/simplCore/should_compile/T3772.stdout
+++ b/testsuite/tests/simplCore/should_compile/T3772.stdout
@@ -69,10 +69,10 @@ foo [InlPrag=[final]] :: Int -> ()
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=False)
-         Tmpl= \ (w [Occ=Once1!] :: Int) ->
-                 case w of { GHC.Types.I# ww [Occ=Once1] -> T3772.$wfoo ww }}]
+         Tmpl= \ (n [Occ=Once1!] :: Int) ->
+                 case n of { GHC.Types.I# ww [Occ=Once1] -> T3772.$wfoo ww }}]
 foo
-  = \ (w :: Int) -> case w of { GHC.Types.I# ww -> T3772.$wfoo ww }
+  = \ (n :: Int) -> case n of { GHC.Types.I# ww -> T3772.$wfoo ww }
 
 
 
diff --git a/testsuite/tests/simplCore/should_compile/T4908.stderr b/testsuite/tests/simplCore/should_compile/T4908.stderr
index f8f9107485..afea396826 100644
--- a/testsuite/tests/simplCore/should_compile/T4908.stderr
+++ b/testsuite/tests/simplCore/should_compile/T4908.stderr
@@ -63,10 +63,10 @@ T4908.$wf [InlPrag=[2]] :: Int# -> (Int, Int) -> Bool
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True, Guidance=IF_ARGS [30 20] 101 20}]
 T4908.$wf
-  = \ (ww :: Int#) (w :: (Int, Int)) ->
+  = \ (ww :: Int#) (x :: (Int, Int)) ->
       case ww of ds {
         __DEFAULT ->
-          case w of { (a, b) ->
+          case x of { (a, b) ->
           case b of { I# ds1 ->
           case ds1 of ds2 {
             __DEFAULT -> T4908.f_$s$wf a ds2 (-# ds 1#);
@@ -85,10 +85,10 @@ f [InlPrag=[2]] :: Int -> (Int, Int) -> Bool
  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, Int)) ->
-                 case w of { I# ww [Occ=Once1] -> T4908.$wf ww w1 }}]
-f = \ (w :: Int) (w1 :: (Int, Int)) ->
-      case w of { I# ww -> T4908.$wf ww w1 }
+         Tmpl= \ (ds [Occ=Once1!] :: Int) (x [Occ=Once1] :: (Int, Int)) ->
+                 case ds of { I# ww [Occ=Once1] -> T4908.$wf ww x }}]
+f = \ (ds :: Int) (x :: (Int, Int)) ->
+      case ds of { I# ww -> T4908.$wf ww x }
 
 
 ------ Local rules for imported ids --------
diff --git a/testsuite/tests/simplCore/should_compile/T4930.stderr b/testsuite/tests/simplCore/should_compile/T4930.stderr
index 3321809415..9da0009f84 100644
--- a/testsuite/tests/simplCore/should_compile/T4930.stderr
+++ b/testsuite/tests/simplCore/should_compile/T4930.stderr
@@ -61,15 +61,15 @@ foo [InlPrag=[2]] :: Int -> Int
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=False)
-         Tmpl= \ (w [Occ=Once1!] :: Int) ->
-                 case w of { GHC.Types.I# ww [Occ=Once1] ->
+         Tmpl= \ (n [Occ=Once1!] :: Int) ->
+                 case n of { GHC.Types.I# ww [Occ=Once1] ->
                  case T4930.$wfoo ww of ww1 [Occ=Once1] { __DEFAULT ->
                  GHC.Types.I# ww1
                  }
                  }}]
 foo
-  = \ (w :: Int) ->
-      case w of { GHC.Types.I# ww ->
+  = \ (n :: Int) ->
+      case n of { GHC.Types.I# ww ->
       case T4930.$wfoo ww of ww1 { __DEFAULT -> GHC.Types.I# ww1 }
       }
 
diff --git a/testsuite/tests/simplCore/should_compile/T5298.stdout b/testsuite/tests/simplCore/should_compile/T5298.stdout
index 67b106c3be..661e893028 100644
--- a/testsuite/tests/simplCore/should_compile/T5298.stdout
+++ b/testsuite/tests/simplCore/should_compile/T5298.stdout
@@ -6,8 +6,8 @@ $wg
         0# -> 1#
       }
 --
-g = \ w ->
-      case w of { I# ww -> case $wg ww of ww1 { __DEFAULT -> I# ww1 } }
+g = \ ds ->
+      case ds of { I# ww -> case $wg ww of ww1 { __DEFAULT -> I# ww1 } }
 
 
 ------ Local rules for imported ids --------
diff --git a/testsuite/tests/simplCore/should_compile/T8331.stderr b/testsuite/tests/simplCore/should_compile/T8331.stderr
index e84edead21..7219016651 100644
--- a/testsuite/tests/simplCore/should_compile/T8331.stderr
+++ b/testsuite/tests/simplCore/should_compile/T8331.stderr
@@ -16,7 +16,7 @@
                       ReaderT r (ST s) a -> ReaderT r (ST s) b -> ReaderT r (ST s) b))
 "SPEC $c>> @(ST s) _"
     forall (@s) (@r) ($dMonad :: Monad (ST s)).
-      $fMonadReaderT_$c>> @(ST s) @r $dMonad
+      $fMonadReaderT1 @(ST s) @r $dMonad
       = $fMonadAbstractIOSTReaderT_$s$c>> @s @r
 "SPEC $cliftA2 @(ST s) _"
     forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
diff --git a/testsuite/tests/simplCore/should_compile/spec-inline.stderr b/testsuite/tests/simplCore/should_compile/spec-inline.stderr
index 319eba03cb..2ba178e6bf 100644
--- a/testsuite/tests/simplCore/should_compile/spec-inline.stderr
+++ b/testsuite/tests/simplCore/should_compile/spec-inline.stderr
@@ -80,12 +80,12 @@ Roman.$wgo [InlPrag=[2]] :: Maybe Int -> Maybe Int -> GHC.Prim.Int#
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True, Guidance=IF_ARGS [61 30] 249 0}]
 Roman.$wgo
-  = \ (w :: Maybe Int) (w1 :: Maybe Int) ->
-      case w1 of {
+  = \ (u :: Maybe Int) (ds :: Maybe Int) ->
+      case ds of {
         Nothing -> case Roman.foo3 of wild1 { };
         Just x ->
           case x of { GHC.Types.I# ipv ->
-          case w of {
+          case u of {
             Nothing -> Roman.foo_$s$wgo (GHC.Prim.*# 7# ipv) 10#;
             Just n ->
               case n of { GHC.Types.I# x2 ->
@@ -116,14 +116,14 @@ Roman.foo_go [InlPrag=[2]] :: Maybe Int -> Maybe 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] :: Maybe Int)
-                 (w1 [Occ=Once1] :: Maybe Int) ->
-                 case Roman.$wgo w w1 of ww [Occ=Once1] { __DEFAULT ->
+         Tmpl= \ (u [Occ=Once1] :: Maybe Int)
+                 (ds [Occ=Once1] :: Maybe Int) ->
+                 case Roman.$wgo u ds of ww [Occ=Once1] { __DEFAULT ->
                  GHC.Types.I# ww
                  }}]
 Roman.foo_go
-  = \ (w :: Maybe Int) (w1 :: Maybe Int) ->
-      case Roman.$wgo w w1 of ww { __DEFAULT -> GHC.Types.I# ww }
+  = \ (u :: Maybe Int) (ds :: Maybe Int) ->
+      case Roman.$wgo u ds of ww { __DEFAULT -> GHC.Types.I# ww }
 
 -- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
 Roman.foo2 :: Int
diff --git a/testsuite/tests/stranal/should_compile/T16029.stdout b/testsuite/tests/stranal/should_compile/T16029.stdout
index 2d1f2106f3..76bf2617fb 100644
--- a/testsuite/tests/stranal/should_compile/T16029.stdout
+++ b/testsuite/tests/stranal/should_compile/T16029.stdout
@@ -4,8 +4,8 @@
   :: GHC.Prim.Int# -> GHC.Prim.Int#
   = \ (ww :: GHC.Prim.Int#) ->
 g2 [InlPrag=[2]] :: T -> Int -> Int
-         Tmpl= \ (w [Occ=Once1!] :: T) (w1 [Occ=Once1!] :: Int) ->
-  = \ (w :: T) (w1 :: Int) ->
+         Tmpl= \ (ds [Occ=Once1!] :: T) (ds1 [Occ=Once1!] :: Int) ->
+  = \ (ds :: T) (ds1 :: Int) ->
 g1 [InlPrag=[2]] :: S -> Int -> Int
-         Tmpl= \ (w [Occ=Once1!] :: S) (w1 [Occ=Once1!] :: Int) ->
-  = \ (w :: S) (w1 :: Int) ->
+         Tmpl= \ (ds [Occ=Once1!] :: S) (ds1 [Occ=Once1!] :: Int) ->
+  = \ (ds :: S) (ds1 :: Int) ->
diff --git a/testsuite/tests/stranal/should_compile/T19766.hs b/testsuite/tests/stranal/should_compile/T19766.hs
new file mode 100644
index 0000000000..1062c57cc1
--- /dev/null
+++ b/testsuite/tests/stranal/should_compile/T19766.hs
@@ -0,0 +1,19 @@
+{-# OPTIONS_GHC -O #-}
+
+module T19766 where
+
+data T a b = T !a !b
+
+data HasT = A (T Int Int) | B (T Int Int)
+
+getT :: HasT -> T Int Int
+getT (A t) = t
+getT (B t) = t
+
+f :: HasT -> [Int]
+f ht = case getT ht of t@(T _ _) -> reverse $ reverse $ reverse $ reverse $ reverse $ reverse $ lookupGRE t 15 [1,2,3,4]
+{-# NOINLINE f #-}
+
+lookupGRE :: T Int a -> Int -> [Int] -> [Int]
+lookupGRE ~(T n _) !k xs = [ x | x <- xs, x+k == n ]
+{-# NOINLINE lookupGRE #-}
diff --git a/testsuite/tests/stranal/should_compile/all.T b/testsuite/tests/stranal/should_compile/all.T
index f5ebbf289a..9a210ea165 100644
--- a/testsuite/tests/stranal/should_compile/all.T
+++ b/testsuite/tests/stranal/should_compile/all.T
@@ -66,6 +66,7 @@ test('T18894b',  [ grep_errmsg(r'Arity=2') ], compile, ['-ddump-stranal -dsuppre
 test('T18982',  [ grep_errmsg(r'\$w. .*Int#$') ], compile, ['-dppr-cols=1000 -ddump-simpl -dsuppress-idinfo -dsuppress-uniques'])
 
 test('T19180', normal, compile, [''])
+test('T19766', [ grep_errmsg(r'absentError') ], compile, ['-ddump-worker-wrapper'])
 test('T19849', normal, compile, [''])
 test('T19882a', normal, compile, [''])
 test('T19882b', normal, compile, [''])