Rubbish literals for all representations (#18983)

This patch cleans up the complexity around WW's `mk_absent_let` by
broadening the scope of `LitRubbish`. Rubbish literals now store the
`PrimRep` they represent and are ultimately lowered in Cmm.
This in turn allows absent literals of `VecRep` or `VoidRep`. The latter
allows absent literals for unlifted coercions, as requested in #18983.

I took the liberty to rewrite and clean up `Note [Absent fillers]` and
`Note [Rubbish values]` to account for the new implementation and to
make them more orthogonal in their description.

I didn't add a new regression test, as `T18982` already contains the
test in the ticket and its test output changes as expected.

Fixes #18983.

1 files changed, 15 insertions, 15 deletions

diff --git a/testsuite/tests/stranal/should_compile/T18982.stderr b/testsuite/tests/stranal/should_compile/T18982.stderr
index 3e6074e759..310eed5cc3 100644
--- a/testsuite/tests/stranal/should_compile/T18982.stderr
+++ b/testsuite/tests/stranal/should_compile/T18982.stderr
@@ -1,8 +1,8 @@
 
 ==================== Tidy Core ====================
-Result size of Tidy Core = {terms: 311, types: 249, coercions: 4, joins: 0/0}
+Result size of Tidy Core = {terms: 315, types: 214, coercions: 2, joins: 0/0}
 
--- RHS size: {terms: 8, types: 11, coercions: 1, joins: 0/0}
+-- RHS size: {terms: 8, types: 9, coercions: 1, joins: 0/0}
 T18982.$WExGADT :: forall e. (e ~ Int) => e %1 -> Int %1 -> ExGADT Int
 T18982.$WExGADT = \ (@e) (dt :: e ~ Int) (dt :: e) (dt :: Int) -> T18982.ExGADT @Int @e @~(<Int>_N :: Int GHC.Prim.~# Int) dt dt dt
 
@@ -10,7 +10,7 @@ T18982.$WExGADT = \ (@e) (dt :: e ~ Int) (dt :: e) (dt :: Int) -> T18982.ExGADT
 T18982.$WGADT :: Int %1 -> GADT Int
 T18982.$WGADT = \ (dt :: Int) -> T18982.GADT @Int @~(<Int>_N :: Int GHC.Prim.~# Int) dt
 
--- RHS size: {terms: 7, types: 8, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 7, types: 6, coercions: 0, joins: 0/0}
 T18982.$WEx :: forall e a. e %1 -> a %1 -> Ex a
 T18982.$WEx = \ (@e) (@a) (dt :: e) (dt :: a) -> T18982.Ex @a @e dt dt
 
@@ -210,27 +210,27 @@ T18982.$tc'ExGADT2 = GHC.Types.TrNameS T18982.$tc'ExGADT3
 T18982.$tc'ExGADT :: GHC.Types.TyCon
 T18982.$tc'ExGADT = GHC.Types.TyCon 8468257409157161049## 5503123603717080600## T18982.$trModule T18982.$tc'ExGADT2 1# T18982.$tc'ExGADT1
 
--- RHS size: {terms: 11, types: 14, coercions: 0, joins: 0/0}
-T18982.$wi :: forall {a} {e}. (a GHC.Prim.~# Int) -> e -> GHC.Prim.Int# -> GHC.Prim.Int#
-T18982.$wi = \ (@a) (@e) (ww :: a GHC.Prim.~# Int) (ww1 :: e) (ww2 :: GHC.Prim.Int#) -> case ww1 of { __DEFAULT -> GHC.Prim.+# ww2 1# }
+-- RHS size: {terms: 13, types: 15, coercions: 0, joins: 0/0}
+T18982.$wi :: forall {a} {e}. e -> GHC.Prim.Int# -> GHC.Prim.Int#
+T18982.$wi = \ (@a) (@e) (ww :: e) (ww1 :: GHC.Prim.Int#) -> case RUBBISH[] @(a GHC.Prim.~# Int) of ww2 { __DEFAULT -> case ww of { __DEFAULT -> GHC.Prim.+# ww1 1# } }
 
--- RHS size: {terms: 15, types: 27, coercions: 1, joins: 0/0}
+-- RHS size: {terms: 15, types: 22, coercions: 0, joins: 0/0}
 i :: forall a. ExGADT a -> Int
-i = \ (@a) (w :: ExGADT a) -> case w of { ExGADT @e ww1 ww2 ww3 ww4 -> case ww4 of { GHC.Types.I# ww6 -> case T18982.$wi @a @e @~(ww1 :: a GHC.Prim.~# Int) ww3 ww6 of ww7 { __DEFAULT -> GHC.Types.I# ww7 } } }
+i = \ (@a) (w :: ExGADT a) -> case w of { ExGADT @e ww1 ww2 ww3 ww4 -> case ww4 of { GHC.Types.I# ww6 -> case T18982.$wi @a @e ww3 ww6 of ww7 { __DEFAULT -> GHC.Types.I# ww7 } } }
 
--- RHS size: {terms: 6, types: 10, coercions: 0, joins: 0/0}
-T18982.$wh :: forall {a}. (a GHC.Prim.~# Int) -> GHC.Prim.Int# -> GHC.Prim.Int#
-T18982.$wh = \ (@a) (ww :: a GHC.Prim.~# Int) (ww1 :: GHC.Prim.Int#) -> GHC.Prim.+# ww1 1#
+-- RHS size: {terms: 8, types: 12, coercions: 0, joins: 0/0}
+T18982.$wh :: forall {a}. GHC.Prim.Int# -> GHC.Prim.Int#
+T18982.$wh = \ (@a) (ww :: GHC.Prim.Int#) -> case RUBBISH[] @(a GHC.Prim.~# Int) of ww1 { __DEFAULT -> GHC.Prim.+# ww 1# }
 
--- RHS size: {terms: 14, types: 18, coercions: 1, joins: 0/0}
+-- RHS size: {terms: 14, types: 15, coercions: 0, joins: 0/0}
 h :: forall a. GADT a -> Int
-h = \ (@a) (w :: GADT a) -> case w of { GADT ww1 ww2 -> case ww2 of { GHC.Types.I# ww4 -> case T18982.$wh @a @~(ww1 :: a GHC.Prim.~# Int) ww4 of ww5 { __DEFAULT -> GHC.Types.I# ww5 } } }
+h = \ (@a) (w :: GADT a) -> case w of { GADT ww1 ww2 -> case ww2 of { GHC.Types.I# ww4 -> case T18982.$wh @a ww4 of ww5 { __DEFAULT -> GHC.Types.I# ww5 } } }
 
--- RHS size: {terms: 9, types: 5, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 9, types: 4, coercions: 0, joins: 0/0}
 T18982.$wg :: forall {e}. e -> GHC.Prim.Int# -> GHC.Prim.Int#
 T18982.$wg = \ (@e) (ww :: e) (ww1 :: GHC.Prim.Int#) -> case ww of { __DEFAULT -> GHC.Prim.+# ww1 1# }
 
--- RHS size: {terms: 14, types: 12, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 14, types: 11, coercions: 0, joins: 0/0}
 g :: Ex Int -> Int
 g = \ (w :: Ex Int) -> case w of { Ex @e ww1 ww2 -> case ww2 of { GHC.Types.I# ww4 -> case T18982.$wg @e ww1 ww4 of ww5 { __DEFAULT -> GHC.Types.I# ww5 } } }