[Git][ghc/ghc][wip/T18894] 2 commits: DmdAnal: Annotate top-level function bindings with demands (#18894)

Sebastian Graf gitlab at gitlab.haskell.org
Fri Nov 27 12:13:53 UTC 2020



Sebastian Graf pushed to branch wip/T18894 at Glasgow Haskell Compiler / GHC


Commits:
b853798a by Sebastian Graf at 2020-11-27T11:41:35+01:00
DmdAnal: Annotate top-level function bindings with demands (#18894)

It's useful to annotate a non-exported top-level function like `g` in

```hs
module Lib (h) where

g :: Int -> Int -> (Int,Int)
g m 1 = (m, 0)
g m n = (2 * m, 2 `div` n)
{-# NOINLINE g #-}

h :: Int -> Int
h 1 = 0
h m
  | odd m     = snd (g m 2)
  | otherwise = uncurry (+) (g 2 m)
```

with its demand `UCU(CS(P(1P(U),SP(U))`, which tells us that whenever `g` was
called, the second component of the returned pair was evaluated strictly.

Since #18903 we do so for local functions, where we can see all calls.
For top-level functions, we can assume that all *exported* functions are
demanded according to `topDmd` and thus get sound demands for
non-exported top-level functions.

The demand on `g` is crucial information for Nested CPR, which may the
go on and unbox `g` for the second pair component. That is true even if
that pair component may diverge, as is the case for the call site `g 13
0`, which throws a div-by-zero exception.

We only track bindings of function type in order not to risk huge compile-time
regressions, see `isInterestingTopLevelFn`.

Fixes #18894.

- - - - -
3a7344fb by Sebastian Graf at 2020-11-27T13:03:07+01:00
Demand: Simplify `CU(U)` to `U` (#19005)

Both sub-demands encode the same information.
This is a trivial change and already affects a few regression tests
(e.g. `T5075`), so no separate regression test is necessary.

- - - - -


13 changed files:

- compiler/GHC/Core/FVs.hs
- compiler/GHC/Core/Opt/DmdAnal.hs
- compiler/GHC/Core/Opt/Pipeline.hs
- compiler/GHC/Core/Opt/WorkWrap/Utils.hs
- compiler/GHC/Core/Tidy.hs
- compiler/GHC/Types/Demand.hs
- compiler/GHC/Types/Id/Info.hs
- testsuite/tests/arityanal/should_compile/Arity11.stderr
- testsuite/tests/arityanal/should_compile/Arity16.stderr
- + testsuite/tests/stranal/should_compile/T18894.hs
- + testsuite/tests/stranal/should_compile/T18894.stderr
- testsuite/tests/stranal/should_compile/all.T
- testsuite/tests/stranal/sigs/T5075.stderr


Changes:

=====================================
compiler/GHC/Core/FVs.hs
=====================================
@@ -525,12 +525,11 @@ ruleLhsFVIds (Rule { ru_bndrs = bndrs, ru_args = args })
   = filterFV isLocalId $ addBndrs bndrs (exprs_fvs args)
 
 ruleRhsFreeIds :: CoreRule -> VarSet
--- ^ This finds all locally-defined free Ids on the left hand side of a rule
+-- ^ This finds all locally-defined free Ids on the right hand side of a rule
 -- and returns them as a non-deterministic set
 ruleRhsFreeIds (BuiltinRule {}) = emptyVarSet
-ruleRhsFreeIds (Rule { ru_bndrs = bndrs, ru_args = args })
-  = fvVarSet $ filterFV isLocalId $
-     addBndrs bndrs $ exprs_fvs args
+ruleRhsFreeIds (Rule { ru_bndrs = bndrs, ru_rhs = rhs })
+  = fvVarSet $ filterFV isLocalId $ addBndrs bndrs $ expr_fvs rhs
 
 {-
 Note [Rule free var hack]  (Not a hack any more)


=====================================
compiler/GHC/Core/Opt/DmdAnal.hs
=====================================
@@ -37,6 +37,7 @@ import GHC.Core.Type
 import GHC.Core.FVs      ( exprFreeIds, ruleRhsFreeIds )
 import GHC.Core.Coercion ( Coercion, coVarsOfCo )
 import GHC.Core.FamInstEnv
+import GHC.Core.Opt.Arity ( typeArity )
 import GHC.Utils.Misc
 import GHC.Utils.Panic
 import GHC.Data.Maybe         ( isJust )
@@ -59,33 +60,62 @@ data DmdAnalOpts = DmdAnalOpts
    { dmd_strict_dicts :: !Bool -- ^ Use strict dictionaries
    }
 
+-- | Whether we want to store demands on a top-level Id or just default
+-- to 'topDmd'.
+--
+-- Basically, we want to now how top-level *functions* are *used*
+-- (e.g. called), but aren't interested in whether they were called strictly
+-- or not. Other top-level bindings are boring.
+isInterestingTopLevelFn :: Id -> Bool
+-- SG tried to set this to True and got a +2% ghc/alloc regression in T5642
+-- (which is dominated by the Simplifier) at no gain in analysis precision.
+-- If there was a gain, that regression might be acceptable.
+-- Plus, we could use LetUp for thunks and share some code with local let
+-- bindings.
+isInterestingTopLevelFn id =
+  typeArity (idType id) `lengthExceeds` 0
+
 -- | Outputs a new copy of the Core program in which binders have been annotated
 -- with demand and strictness information.
 --
 -- Note: use `seqBinds` on the result to avoid leaks due to lazyness (cf Note
 -- [Stamp out space leaks in demand analysis])
-dmdAnalProgram :: DmdAnalOpts -> FamInstEnvs -> CoreProgram -> CoreProgram
-dmdAnalProgram opts fam_envs binds = binds_plus_dmds
-   where
-      env             = emptyAnalEnv opts fam_envs
-      binds_plus_dmds = snd $ mapAccumL dmdAnalTopBind env binds
-
--- Analyse a (group of) top-level binding(s)
-dmdAnalTopBind :: AnalEnv
-               -> CoreBind
-               -> (AnalEnv, CoreBind)
-dmdAnalTopBind env (NonRec id rhs)
-  = ( extendAnalEnv TopLevel env id sig
-    , NonRec (setIdStrictness id sig) rhs')
+dmdAnalProgram :: DmdAnalOpts -> FamInstEnvs -> [CoreRule] -> CoreProgram -> CoreProgram
+dmdAnalProgram opts fam_envs rules binds
+  = snd $ go (emptyAnalEnv opts fam_envs) binds
   where
-    ( _, sig, rhs') = dmdAnalRhsLetDown Nothing env topSubDmd id rhs
+    go _   []     = (nopDmdType, [])
+    go env (b:bs) = case b of
+      NonRec id rhs
+        | (env', lazy_fvs, id', rhs') <- dmdAnalRhsLetDown TopLevel NonRecursive env topSubDmd id rhs
+        , (dmd_ty', bs') <- go env' bs
+        , let dmd_ty'' = add_exported_use env' dmd_ty' id' `addLazyFVs` lazy_fvs
+        , (!dmd_ty''', id_dmd) <- findBndrDmd env' False dmd_ty'' id'
+        , let id'' = annotate_id_dmd id' id_dmd
+        -> (dmd_ty''', NonRec id'' rhs' : bs')
+      Rec pairs
+        | (env', lazy_fvs, pairs') <- dmdFix TopLevel env topSubDmd pairs
+        , let ids' = map fst pairs'
+        , (dmd_ty', bs') <- go env' bs
+        , let dmd_ty'' = add_exported_uses env' dmd_ty' ids' `addLazyFVs` lazy_fvs
+        , (!dmd_ty''', id_dmds) <- findBndrsDmds env' dmd_ty'' ids'
+        , let pairs'' = zipWith (\(id', rhs') dmd -> (annotate_id_dmd id' dmd, rhs')) pairs' id_dmds
+        -> (dmd_ty''', Rec pairs'' : bs')
+
+    annotate_id_dmd id dmd
+      | isInterestingTopLevelFn id
+      = id `setIdDemandInfo` dmd
+      | otherwise
+      = id `setIdDemandInfo` topDmd
 
-dmdAnalTopBind env (Rec pairs)
-  = (env', Rec pairs')
-  where
-    (env', _, pairs')  = dmdFix TopLevel env topSubDmd pairs
-                -- We get two iterations automatically
-                -- c.f. the NonRec case above
+    add_exported_uses env = foldl' (add_exported_use env)
+    add_exported_use env dmd_ty id
+      | isExportedId id || elemVarSet id rule_fvs
+      -- See Note [Absence analysis for stable unfoldings and RULES]
+      = dmd_ty `plusDmdType` fst (dmdAnalStar env topDmd (Var id))
+      | otherwise       = dmd_ty
+
+    rule_fvs = foldr (unionVarSet . ruleRhsFreeIds) emptyVarSet rules
 
 {- Note [Stamp out space leaks in demand analysis]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -194,7 +224,7 @@ dmdAnal' env dmd (App fun arg)
     -- Crucially, coercions /are/ handled here, because they are
     -- value arguments (#10288)
     let
-        call_dmd          = mkCallDmd dmd
+        call_dmd          = mkCalledOnceDmd dmd
         (fun_ty, fun')    = dmdAnal env call_dmd fun
         (arg_dmd, res_ty) = splitDmdTy fun_ty
         (arg_ty, arg')    = dmdAnalStar env (dmdTransformThunkDmd arg arg_dmd) arg
@@ -320,9 +350,7 @@ dmdAnal' env dmd (Let (NonRec id rhs) body)
 dmdAnal' env dmd (Let (NonRec id rhs) body)
   = (body_ty2, Let (NonRec id2 rhs') body')
   where
-    (lazy_fv, sig, rhs') = dmdAnalRhsLetDown Nothing env dmd id rhs
-    id1                  = setIdStrictness id sig
-    env1                 = extendAnalEnv NotTopLevel env id sig
+    (env1, lazy_fv, id1, rhs') = dmdAnalRhsLetDown NotTopLevel NonRecursive env dmd id rhs
     (body_ty, body')     = dmdAnal env1 dmd body
     (body_ty1, id2)      = annotateBndr env body_ty id1
     body_ty2             = addLazyFVs body_ty1 lazy_fv -- see Note [Lazy and unleashable free variables]
@@ -344,8 +372,8 @@ dmdAnal' env dmd (Let (Rec pairs) body)
   = let
         (env', lazy_fv, pairs') = dmdFix NotTopLevel env dmd pairs
         (body_ty, body')        = dmdAnal env' dmd body
-        body_ty1                = deleteFVs body_ty (map fst pairs)
-        body_ty2                = addLazyFVs body_ty1 lazy_fv -- see Note [Lazy and unleashable free variables]
+        body_ty1                = addLazyFVs body_ty lazy_fv -- see Note [Lazy and unleashable free variables]
+        body_ty2                = deleteFVs body_ty1 (map fst pairs) -- TODO: We could annotate idDemandInfo here
     in
     body_ty2 `seq`
     (body_ty2,  Let (Rec pairs') body')
@@ -582,9 +610,13 @@ dmdTransform env var dmd
   | Just (sig, top_lvl) <- lookupSigEnv env var
   , let fn_ty = dmdTransformSig sig dmd
   = -- pprTrace "dmdTransform:LetDown" (vcat [ppr var, ppr sig, ppr dmd, ppr fn_ty]) $
-    if isTopLevel top_lvl
-    then fn_ty   -- Don't record demand on top-level things
-    else addVarDmd fn_ty var (C_11 :* dmd)
+    case top_lvl of
+      NotTopLevel -> addVarDmd fn_ty var (C_11 :* dmd)
+      TopLevel
+        | isInterestingTopLevelFn var
+        -> addVarDmd fn_ty var (C_0N `multDmd` (C_11 :* dmd)) -- discard strictness
+        | otherwise
+        -> fn_ty -- don't bother tracking; just annotate with 'topDmd' later
   -- Everything else:
   --   * Local let binders for which we use LetUp (cf. 'useLetUp')
   --   * Lambda binders
@@ -612,33 +644,36 @@ dmdTransform env var dmd
 --
 -- This is the LetDown rule in the paper “Higher-Order Cardinality Analysis”.
 dmdAnalRhsLetDown
-  :: Maybe [Id]   -- Just bs <=> recursive, Nothing <=> non-recursive
+  :: TopLevelFlag
+  -> RecFlag
   -> AnalEnv -> SubDemand
   -> Id -> CoreExpr
-  -> (DmdEnv, StrictSig, CoreExpr)
+  -> (AnalEnv, DmdEnv, Id, CoreExpr)
 -- Process the RHS of the binding, add the strictness signature
 -- to the Id, and augment the environment with the signature as well.
 -- See Note [NOINLINE and strictness]
-dmdAnalRhsLetDown rec_flag env let_dmd id rhs
+dmdAnalRhsLetDown top_lvl rec_flag env let_dmd id rhs
   = -- pprTrace "dmdAnalRhsLetDown" (ppr id $$ ppr let_dmd $$ ppr sig $$ ppr lazy_fv) $
-    (lazy_fv, sig, rhs')
+    (env', lazy_fv, id', rhs')
   where
     rhs_arity = idArity id
+    -- See Note [Demand signatures are computed for a threshold demand based on idArity]
     rhs_dmd -- See Note [Demand analysis for join points]
             -- See Note [Invariants on join points] invariant 2b, in GHC.Core
             --     rhs_arity matches the join arity of the join point
             | isJoinId id
-            = mkCallDmds rhs_arity let_dmd
+            = mkCalledOnceDmds rhs_arity let_dmd
             | otherwise
-            -- NB: rhs_arity
-            -- See Note [Demand signatures are computed for a threshold demand based on idArity]
-            = mkRhsDmd env rhs_arity rhs
+            = mkCalledOnceDmds rhs_arity topSubDmd
 
     (rhs_dmd_ty, rhs') = dmdAnal env rhs_dmd rhs
     DmdType rhs_fv rhs_dmds rhs_div = rhs_dmd_ty
 
     sig = mkStrictSigForArity rhs_arity (DmdType sig_fv rhs_dmds rhs_div)
 
+    id' = id `setIdStrictness` sig
+    env' = extendAnalEnv top_lvl env id' sig
+
     -- See Note [Aggregated demand for cardinality]
     -- FIXME: That Note doesn't explain the following lines at all. The reason
     --        is really much different: When we have a recursive function, we'd
@@ -651,8 +686,8 @@ dmdAnalRhsLetDown rec_flag env let_dmd id rhs
     --        we'd have to do an additional iteration. reuseEnv makes sure that
     --        we never get used-once info for FVs of recursive functions.
     rhs_fv1 = case rec_flag of
-                Just bs -> reuseEnv (delVarEnvList rhs_fv bs)
-                Nothing -> rhs_fv
+                Recursive    -> reuseEnv rhs_fv
+                NonRecursive -> rhs_fv
 
     rhs_fv2 = rhs_fv1 `keepAliveDmdEnv` extra_fvs
     -- Find the RHS free vars of the unfoldings and RULES
@@ -669,13 +704,6 @@ dmdAnalRhsLetDown rec_flag env let_dmd id rhs
             = exprFreeIds unf_body
             | otherwise = emptyVarSet
 
--- | @mkRhsDmd env rhs_arity rhs@ creates a 'SubDemand' for
--- unleashing on the given function's @rhs@, by creating
--- a call demand of @rhs_arity@
--- See Historical Note [Product demands for function body]
-mkRhsDmd :: AnalEnv -> Arity -> CoreExpr -> SubDemand
-mkRhsDmd _env rhs_arity _rhs = mkCallDmds rhs_arity topSubDmd
-
 -- | If given the (local, non-recursive) let-bound 'Id', 'useLetUp' determines
 -- whether we should process the binding up (body before rhs) or down (rhs
 -- before body).
@@ -939,8 +967,6 @@ dmdFix :: TopLevelFlag
 dmdFix top_lvl env let_dmd orig_pairs
   = loop 1 initial_pairs
   where
-    bndrs = map fst orig_pairs
-
     -- See Note [Initialising strictness]
     initial_pairs | ae_virgin env = [(setIdStrictness id botSig, rhs) | (id, rhs) <- orig_pairs ]
                   | otherwise     = orig_pairs
@@ -990,10 +1016,8 @@ dmdFix top_lvl env let_dmd orig_pairs
           = -- pprTrace "my_downRhs" (ppr id $$ ppr (idStrictness id) $$ ppr sig) $
             ((env', lazy_fv'), (id', rhs'))
           where
-            (lazy_fv1, sig, rhs') = dmdAnalRhsLetDown (Just bndrs) env let_dmd id rhs
-            lazy_fv'              = plusVarEnv_C plusDmd lazy_fv lazy_fv1
-            env'                  = extendAnalEnv top_lvl env id sig
-            id'                   = setIdStrictness id sig
+            (env', lazy_fv1, id', rhs') = dmdAnalRhsLetDown top_lvl Recursive env let_dmd id rhs
+            lazy_fv'                    = plusVarEnv_C plusDmd lazy_fv lazy_fv1
 
     zapIdStrictness :: [(Id, CoreExpr)] -> [(Id, CoreExpr)]
     zapIdStrictness pairs = [(setIdStrictness id nopSig, rhs) | (id, rhs) <- pairs ]


=====================================
compiler/GHC/Core/Opt/Pipeline.hs
=====================================
@@ -65,6 +65,7 @@ import GHC.Types.SrcLoc
 import GHC.Types.Id
 import GHC.Types.Id.Info
 import GHC.Types.Basic
+import GHC.Types.Demand ( zapDmdEnvSig )
 import GHC.Types.Var.Set
 import GHC.Types.Var.Env
 import GHC.Types.Unique.Supply ( UniqSupply, mkSplitUniqSupply, splitUniqSupply )
@@ -495,7 +496,7 @@ doCorePass CoreDoExitify             = {-# SCC "Exitify" #-}
                                        doPass exitifyProgram
 
 doCorePass CoreDoDemand              = {-# SCC "DmdAnal" #-}
-                                       doPassDFM dmdAnal
+                                       doPassDFRM dmdAnal
 
 doCorePass CoreDoCpr                 = {-# SCC "CprAnal" #-}
                                        doPassDFM cprAnalProgram
@@ -575,6 +576,13 @@ doPassDFM do_pass guts = do
     let fam_envs = (p_fam_env, mg_fam_inst_env guts)
     doPassM (liftIO . do_pass dflags fam_envs) guts
 
+doPassDFRM :: (DynFlags -> FamInstEnvs -> [CoreRule] -> CoreProgram -> IO CoreProgram) -> ModGuts -> CoreM ModGuts
+doPassDFRM do_pass guts = do
+    dflags <- getDynFlags
+    p_fam_env <- getPackageFamInstEnv
+    let fam_envs = (p_fam_env, mg_fam_inst_env guts)
+    doPassM (liftIO . do_pass dflags fam_envs (mg_rules guts)) guts
+
 doPassDFU :: (DynFlags -> FamInstEnvs -> UniqSupply -> CoreProgram -> CoreProgram) -> ModGuts -> CoreM ModGuts
 doPassDFU do_pass guts = do
     dflags <- getDynFlags
@@ -1088,13 +1096,13 @@ transferIdInfo exported_id local_id
 
 
 
-dmdAnal :: DynFlags -> FamInstEnvs -> CoreProgram -> IO CoreProgram
-dmdAnal dflags fam_envs binds = do
+dmdAnal :: DynFlags -> FamInstEnvs -> [CoreRule] -> CoreProgram -> IO CoreProgram
+dmdAnal dflags fam_envs rules binds = do
   let opts = DmdAnalOpts
                { dmd_strict_dicts = gopt Opt_DictsStrict dflags
                }
-      binds_plus_dmds = dmdAnalProgram opts fam_envs binds
+      binds_plus_dmds = dmdAnalProgram opts fam_envs rules binds
   Err.dumpIfSet_dyn dflags Opt_D_dump_str_signatures "Strictness signatures" FormatText $
-    dumpIdInfoOfProgram (ppr . strictnessInfo) binds_plus_dmds
+    dumpIdInfoOfProgram (ppr . zapDmdEnvSig . strictnessInfo) binds_plus_dmds
   -- See Note [Stamp out space leaks in demand analysis] in GHC.Core.Opt.DmdAnal
   seqBinds binds_plus_dmds `seq` return binds_plus_dmds


=====================================
compiler/GHC/Core/Opt/WorkWrap/Utils.hs
=====================================
@@ -1275,10 +1275,14 @@ mk_absent_let dflags fam_envs arg
 
     abs_rhs      = mkAbsentErrorApp arg_ty msg
     msg          = showSDoc (gopt_set dflags Opt_SuppressUniques)
-                            (ppr arg <+> ppr (idType arg) <+> file_msg)
+                            (vcat
+                              [ text "Arg:" <+> ppr arg
+                              , text "Type:" <+> ppr arg_ty
+                              , file_msg
+                              ])
     file_msg     = case outputFile dflags of
                      Nothing -> empty
-                     Just f  -> text "in output file " <+> quotes (text f)
+                     Just f  -> text "In output file " <+> quotes (text f)
               -- We need to suppress uniques here because otherwise they'd
               -- end up in the generated code as strings. This is bad for
               -- determinism, because with different uniques the strings


=====================================
compiler/GHC/Core/Tidy.hs
=====================================
@@ -21,7 +21,7 @@ import GHC.Core
 import GHC.Core.Seq ( seqUnfolding )
 import GHC.Types.Id
 import GHC.Types.Id.Info
-import GHC.Types.Demand ( zapUsageEnvSig )
+import GHC.Types.Demand ( zapDmdEnvSig )
 import GHC.Core.Type     ( tidyType, tidyVarBndr )
 import GHC.Core.Coercion ( tidyCo )
 import GHC.Types.Var
@@ -206,7 +206,7 @@ tidyLetBndr rec_tidy_env env@(tidy_env, var_env) id
         new_info = vanillaIdInfo
                     `setOccInfo`        occInfo old_info
                     `setArityInfo`      arityInfo old_info
-                    `setStrictnessInfo` zapUsageEnvSig (strictnessInfo old_info)
+                    `setStrictnessInfo` zapDmdEnvSig (strictnessInfo old_info)
                     `setDemandInfo`     demandInfo old_info
                     `setInlinePragInfo` inlinePragInfo old_info
                     `setUnfoldingInfo`  new_unf


=====================================
compiler/GHC/Types/Demand.hs
=====================================
@@ -34,7 +34,7 @@ module GHC.Types.Demand (
     lazyApply1Dmd, lazyApply2Dmd, strictOnceApply1Dmd, strictManyApply1Dmd,
     -- ** Other @Demand@ operations
     oneifyCard, oneifyDmd, strictifyDmd, strictifyDictDmd, mkWorkerDemand,
-    peelCallDmd, peelManyCalls, mkCallDmd, mkCallDmds,
+    peelCallDmd, peelManyCalls, mkCalledOnceDmd, mkCalledOnceDmds,
     addCaseBndrDmd,
     -- ** Extracting one-shot information
     argOneShots, argsOneShots, saturatedByOneShots,
@@ -73,7 +73,7 @@ module GHC.Types.Demand (
     seqDemand, seqDemandList, seqDmdType, seqStrictSig,
 
     -- * Zapping usage information
-    zapUsageDemand, zapUsageEnvSig, zapUsedOnceDemand, zapUsedOnceSig
+    zapUsageDemand, zapDmdEnvSig, zapUsedOnceDemand, zapUsedOnceSig
   ) where
 
 #include "HsVersions.h"
@@ -278,7 +278,8 @@ data SubDemand
   -- ^ @Call n sd@ describes the evaluation context of @n@ function
   -- applications, where every individual result is evaluated according to @sd at .
   -- @sd@ is /relative/ to a single call, cf. Note [Call demands are relative].
-  -- Used only for values of function type.
+  -- Used only for values of function type. Use the smart constructor 'mkCall'
+  -- whenever possible!
   | Prod ![Demand]
   -- ^ @Prod ds@ describes the evaluation context of a case scrutinisation
   -- on an expression of product type, where the product components are
@@ -306,7 +307,7 @@ polyDmd C_1N = C_1N :* poly1N
 polyDmd C_10 = C_10 :* poly10
 
 -- | A smart constructor for 'Prod', applying rewrite rules along the semantic
--- equalities @Prod [polyDmd n, ...] === polyDmd n@, simplifying to 'Poly'
+-- equality @Prod [polyDmd n, ...] === polyDmd n@, simplifying to 'Poly'
 -- 'SubDemand's when possible. Note that this degrades boxity information! E.g. a
 -- polymorphic demand will never unbox.
 mkProd :: [Demand] -> SubDemand
@@ -335,6 +336,13 @@ viewProd _ _                             = Nothing
 {-# INLINE viewProd #-} -- we want to fuse away the replicate and the allocation
                         -- for Arity. Otherwise, #18304 bites us.
 
+-- | A smart constructor for 'Call', applying rewrite rules along the semantic
+-- equality @Call n (Poly n) === Poly n@, simplifying to 'Poly' 'SubDemand's
+-- when possible.
+mkCall :: Card -> SubDemand -> SubDemand
+mkCall n cd@(Poly m) | n == m = cd
+mkCall n cd                   = Call n cd
+
 -- | @viewCall sd@ interprets @sd@ as a 'Call', expanding 'Poly' demands as
 -- necessary.
 viewCall :: SubDemand -> Maybe (Card, SubDemand)
@@ -356,8 +364,8 @@ lubSubDmd (Prod ds1) (viewProd (length ds1) -> Just ds2) =
 -- Handle Call
 lubSubDmd (Call n1 d1) (viewCall -> Just (n2, d2))
   -- See Note [Call demands are relative]
-  | isAbs n2  = Call (lubCard n1 n2) (lubSubDmd d1 botSubDmd)
-  | otherwise = Call (lubCard n1 n2) (lubSubDmd d1        d2)
+  | isAbs n2  = mkCall (lubCard n1 n2) (lubSubDmd d1 botSubDmd)
+  | otherwise = mkCall (lubCard n1 n2) (lubSubDmd d1        d2)
 -- Handle Poly
 lubSubDmd (Poly n1)  (Poly n2) = Poly (lubCard n1 n2)
 -- Make use of reflexivity (so we'll match the Prod or Call cases again).
@@ -377,8 +385,8 @@ plusSubDmd (Prod ds1) (viewProd (length ds1) -> Just ds2) =
 -- Handle Call
 plusSubDmd (Call n1 d1) (viewCall -> Just (n2, d2))
   -- See Note [Call demands are relative]
-  | isAbs n2  = Call (plusCard n1 n2) (lubSubDmd d1 botSubDmd)
-  | otherwise = Call (plusCard n1 n2) (lubSubDmd d1        d2)
+  | isAbs n2  = mkCall (plusCard n1 n2) (lubSubDmd d1 botSubDmd)
+  | otherwise = mkCall (plusCard n1 n2) (lubSubDmd d1        d2)
 -- Handle Poly
 plusSubDmd (Poly n1)  (Poly n2) = Poly (plusCard n1 n2)
 -- Make use of reflexivity (so we'll match the Prod or Call cases again).
@@ -407,7 +415,7 @@ multSubDmd :: Card -> SubDemand -> SubDemand
 multSubDmd n sd
   | Just sd' <- multTrivial n seqSubDmd sd = sd'
 multSubDmd n (Poly n')    = Poly (multCard n n')
-multSubDmd n (Call n' sd) = Call (multCard n n') sd -- See Note [Call demands are relative]
+multSubDmd n (Call n' sd) = mkCall (multCard n n') sd -- See Note [Call demands are relative]
 multSubDmd n (Prod ds)    = Prod (map (multDmd n) ds)
 
 multDmd :: Card -> Demand -> Demand
@@ -457,22 +465,22 @@ evalDmd = C_1N :* topSubDmd
 -- | First argument of 'GHC.Exts.maskAsyncExceptions#': @SCS(U)@.
 -- Called exactly once.
 strictOnceApply1Dmd :: Demand
-strictOnceApply1Dmd = C_11 :* Call C_11 topSubDmd
+strictOnceApply1Dmd = C_11 :* mkCall C_11 topSubDmd
 
 -- | First argument of 'GHC.Exts.atomically#': @MCM(U)@.
 -- Called at least once, possibly many times.
 strictManyApply1Dmd :: Demand
-strictManyApply1Dmd = C_1N :* Call C_1N topSubDmd
+strictManyApply1Dmd = C_1N :* mkCall C_1N topSubDmd
 
 -- | First argument of catch#: @1C1(U)@.
 -- Evaluates its arg lazily, but then applies it exactly once to one argument.
 lazyApply1Dmd :: Demand
-lazyApply1Dmd = C_01 :* Call C_01 topSubDmd
+lazyApply1Dmd = C_01 :* mkCall C_01 topSubDmd
 
 -- | Second argument of catch#: @1C1(CS(U))@.
 -- Calls its arg lazily, but then applies it exactly once to an additional argument.
 lazyApply2Dmd :: Demand
-lazyApply2Dmd = C_01 :* Call C_01 (Call C_11 topSubDmd)
+lazyApply2Dmd = C_01 :* mkCall C_01 (mkCall C_11 topSubDmd)
 
 -- | Make a 'Demand' evaluated at-most-once.
 oneifyDmd :: Demand -> Demand
@@ -512,12 +520,12 @@ strictifyDictDmd ty (n :* Prod ds)
 strictifyDictDmd _  dmd = dmd
 
 -- | Wraps the 'SubDemand' with a one-shot call demand: @d@ -> @CS(d)@.
-mkCallDmd :: SubDemand -> SubDemand
-mkCallDmd sd = Call C_11 sd
+mkCalledOnceDmd :: SubDemand -> SubDemand
+mkCalledOnceDmd sd = mkCall C_11 sd
 
--- | @mkCallDmds n d@ returns @CS(CS...(CS d))@ where there are @n@ @CS@'s.
-mkCallDmds :: Arity -> SubDemand -> SubDemand
-mkCallDmds arity sd = iterate mkCallDmd sd !! arity
+-- | @mkCalledOnceDmds n d@ returns @CS(CS...(CS d))@ where there are @n@ @CS@'s.
+mkCalledOnceDmds :: Arity -> SubDemand -> SubDemand
+mkCalledOnceDmds arity sd = iterate mkCalledOnceDmd sd !! arity
 
 -- | Peels one call level from the sub-demand, and also returns how many
 -- times we entered the lambda body.
@@ -669,7 +677,7 @@ This is needed even for non-product types, in case the case-binder
 is used but the components of the case alternative are not.
 
 Note [Don't optimise UP(U,U,...) to U]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 These two SubDemands:
    UP(U,U) (@Prod [topDmd, topDmd]@)   and   U (@topSubDmd@)
 are semantically equivalent, but we do not turn the former into
@@ -1571,9 +1579,9 @@ This is weird, so I'm not worried about whether this optimises brilliantly; but
 it should not fall over.
 -}
 
-zapUsageEnvSig :: StrictSig -> StrictSig
--- Remove the usage environment from the demand
-zapUsageEnvSig (StrictSig (DmdType _ ds r)) = mkClosedStrictSig ds r
+-- | Remove the demand environment from the signature.
+zapDmdEnvSig :: StrictSig -> StrictSig
+zapDmdEnvSig (StrictSig (DmdType _ ds r)) = mkClosedStrictSig ds r
 
 zapUsageDemand :: Demand -> Demand
 -- Remove the usage info, but not the strictness info, from the demand
@@ -1615,8 +1623,8 @@ kill_usage kfs (n :* sd) = kill_usage_card kfs n :* kill_usage_sd kfs sd
 
 kill_usage_sd :: KillFlags -> SubDemand -> SubDemand
 kill_usage_sd kfs (Call n sd)
-  | kf_called_once kfs      = Call (lubCard C_1N n) (kill_usage_sd kfs sd)
-  | otherwise               = Call n                (kill_usage_sd kfs sd)
+  | kf_called_once kfs      = mkCall (lubCard C_1N n) (kill_usage_sd kfs sd)
+  | otherwise               = mkCall n                (kill_usage_sd kfs sd)
 kill_usage_sd kfs (Prod ds) = Prod (map (kill_usage kfs) ds)
 kill_usage_sd _   sd        = sd
 
@@ -1640,7 +1648,7 @@ trimToType (n :* sd) ts
   where
     go (Prod ds)   (TsProd tss)
       | equalLength ds tss    = Prod (zipWith trimToType ds tss)
-    go (Call n sd) (TsFun ts) = Call n (go sd ts)
+    go (Call n sd) (TsFun ts) = mkCall n (go sd ts)
     go sd at Poly{}   _          = sd
     go _           _          = topSubDmd
 
@@ -1804,7 +1812,7 @@ instance Binary SubDemand where
     h <- getByte bh
     case h of
       0 -> Poly <$> get bh
-      1 -> Call <$> get bh <*> get bh
+      1 -> mkCall <$> get bh <*> get bh
       2 -> Prod <$> get bh
       _ -> pprPanic "Binary:SubDemand" (ppr (fromIntegral h :: Int))
 


=====================================
compiler/GHC/Types/Id/Info.hs
=====================================
@@ -650,7 +650,7 @@ zapUsageInfo info = Just (info {demandInfo = zapUsageDemand (demandInfo info)})
 zapUsageEnvInfo :: IdInfo -> Maybe IdInfo
 zapUsageEnvInfo info
     | hasDemandEnvSig (strictnessInfo info)
-    = Just (info {strictnessInfo = zapUsageEnvSig (strictnessInfo info)})
+    = Just (info {strictnessInfo = zapDmdEnvSig (strictnessInfo info)})
     | otherwise
     = Nothing
 


=====================================
testsuite/tests/arityanal/should_compile/Arity11.stderr
=====================================
@@ -35,7 +35,7 @@ end Rec }
 
 -- RHS size: {terms: 52, types: 28, coercions: 0, joins: 0/5}
 F11.$wfib [InlPrag=[2]] :: forall {a} {p}. (a -> a -> Bool) -> (Num a, Num p) => a -> p
-[GblId, Arity=4, Str=<MCM(CS(U))><UP(A,UCU(CS(U)),A,A,A,A,UCU(U))><UP(UCU(CS(U)),A,A,A,A,A,1C1(U))><U>, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 150 60 0] 460 0}]
+[GblId, Arity=4, Str=<MCM(CS(U))><UP(A,UCU(CS(U)),A,A,A,A,U)><UP(UCU(CS(U)),A,A,A,A,A,1C1(U))><U>, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 150 60 0] 460 0}]
 F11.$wfib
   = \ (@a) (@p) (ww :: a -> a -> Bool) (w :: Num a) (w1 :: Num p) (w2 :: a) ->
       let {
@@ -73,7 +73,7 @@ F11.$wfib
 fib [InlPrag=[2]] :: forall {a} {p}. (Eq a, Num a, Num p) => a -> p
 [GblId,
  Arity=4,
- Str=<SP(MCM(CS(U)),A)><UP(A,UCU(CS(U)),A,A,A,A,UCU(U))><UP(UCU(CS(U)),A,A,A,A,A,UCU(U))><U>,
+ Str=<SP(MCM(CS(U)),A)><UP(A,UCU(CS(U)),A,A,A,A,U)><UP(UCU(CS(U)),A,A,A,A,A,U)><U>,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=4,unsat_ok=True,boring_ok=False)
          Tmpl= \ (@a) (@p) (w [Occ=Once1!] :: Eq a) (w1 [Occ=Once1] :: Num a) (w2 [Occ=Once1] :: Num p) (w3 [Occ=Once1] :: a) -> case w of { GHC.Classes.C:Eq ww1 [Occ=Once1] _ [Occ=Dead] -> F11.$wfib @a @p ww1 w1 w2 w3 }}]
 fib = \ (@a) (@p) (w :: Eq a) (w1 :: Num a) (w2 :: Num p) (w3 :: a) -> case w of { GHC.Classes.C:Eq ww1 ww2 -> F11.$wfib @a @p ww1 w1 w2 w3 }


=====================================
testsuite/tests/arityanal/should_compile/Arity16.stderr
=====================================
@@ -5,7 +5,7 @@ Result size of Tidy Core = {terms: 52, types: 87, coercions: 0, joins: 0/0}
 Rec {
 -- RHS size: {terms: 15, types: 17, coercions: 0, joins: 0/0}
 map2 [Occ=LoopBreaker] :: forall {t} {a}. (t -> a) -> [t] -> [a]
-[GblId, Arity=2, Str=<UCU(U)><SU>, Unf=OtherCon []]
+[GblId, Arity=2, Str=<U><SU>, Unf=OtherCon []]
 map2
   = \ (@t) (@a) (f :: t -> a) (ds :: [t]) ->
       case ds of {


=====================================
testsuite/tests/stranal/should_compile/T18894.hs
=====================================
@@ -0,0 +1,28 @@
+{-# OPTIONS_GHC -O2 -fforce-recomp #-}
+
+-- | The point of this test is that @g*@ get's a demand that says
+-- "whenever @g*@ is called, the second component of the pair is evaluated strictly".
+module T18894 (h1, h2) where
+
+g1 :: Int -> (Int,Int)
+g1 1 = (15, 0)
+g1 n = (2 * n, 2 `div` n)
+{-# NOINLINE g1 #-}
+
+h1 :: Int -> Int
+h1 1 = 0
+-- Sadly, the @g1 2@ subexpression will be floated to top-level, where we
+-- don't see the specific demand placed on it by @snd at . Tracked in #19001.
+h1 2 = snd (g1 2)
+h1 m = uncurry (+) (g1 m)
+
+g2 :: Int -> Int -> (Int,Int)
+g2 m 1 = (m, 0)
+g2 m n = (2 * m, 2 `div` n)
+{-# NOINLINE g2 #-}
+
+h2 :: Int -> Int
+h2 1 = 0
+h2 m
+  | odd m     = snd (g2 m 2)
+  | otherwise = uncurry (+) (g2 2 m)


=====================================
testsuite/tests/stranal/should_compile/T18894.stderr
=====================================
@@ -0,0 +1,404 @@
+
+==================== Demand analysis ====================
+Result size of Demand analysis
+  = {terms: 177, types: 97, coercions: 0, joins: 0/0}
+
+-- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Prim.Addr#
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 20 0}]
+$trModule = "main"#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Types.TrName
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+$trModule = GHC.Types.TrNameS $trModule
+
+-- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Prim.Addr#
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 30 0}]
+$trModule = "T18894"#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Types.TrName
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+$trModule = GHC.Types.TrNameS $trModule
+
+-- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
+T18894.$trModule :: GHC.Types.Module
+[LclIdX,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+T18894.$trModule = GHC.Types.Module $trModule $trModule
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 0#
+
+-- RHS size: {terms: 36, types: 16, coercions: 0, joins: 0/0}
+g2 [InlPrag=NOINLINE, Dmd=UCU(CS(P(1P(U),SP(U))))]
+  :: Int -> Int -> (Int, Int)
+[LclId,
+ Arity=2,
+ Str=<UP(U)><SP(SU)>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [20 20] 161 20}]
+g2
+  = \ (m [Dmd=UP(U)] :: Int) (ds [Dmd=SP(SU)] :: Int) ->
+      case ds of { GHC.Types.I# ds [Dmd=SU] ->
+      case ds of ds [Dmd=1U] {
+        __DEFAULT ->
+          (case m of { GHC.Types.I# y -> GHC.Types.I# (GHC.Prim.*# 2# y) },
+           case ds of wild {
+             __DEFAULT ->
+               case GHC.Classes.divInt# 2# wild of ww4 { __DEFAULT ->
+               GHC.Types.I# ww4
+               };
+             -1# -> GHC.Types.I# -2#;
+             0# -> case GHC.Real.divZeroError of wild [Dmd=B] { }
+           });
+        1# -> (m, lvl)
+      }
+      }
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 2#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 2#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 0#
+
+-- RHS size: {terms: 36, types: 19, coercions: 0, joins: 0/0}
+h2 :: Int -> Int
+[LclIdX,
+ Arity=1,
+ Str=<SP(MU)>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [20] 162 10}]
+h2
+  = \ (ds [Dmd=SP(MU)] :: Int) ->
+      case ds of wild [Dmd=UP(U)] { GHC.Types.I# ds [Dmd=MU] ->
+      case ds of ds {
+        __DEFAULT ->
+          case GHC.Prim.remInt# ds 2# of {
+            __DEFAULT ->
+              case g2 wild lvl of { (ds1 [Dmd=A], y [Dmd=SU]) -> y };
+            0# ->
+              case g2 lvl wild of { (x [Dmd=SP(U)], ds [Dmd=SP(U)]) ->
+              case x of { GHC.Types.I# x ->
+              case ds of { GHC.Types.I# y -> GHC.Types.I# (GHC.Prim.+# x y) }
+              }
+              }
+          };
+        1# -> lvl
+      }
+      }
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 15#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 0#
+
+-- RHS size: {terms: 3, types: 2, coercions: 0, joins: 0/0}
+lvl :: (Int, Int)
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = (lvl, lvl)
+
+-- RHS size: {terms: 30, types: 11, coercions: 0, joins: 0/0}
+g1 [InlPrag=NOINLINE, Dmd=UCU(P(UP(U),UP(U)))] :: Int -> (Int, Int)
+[LclId,
+ Arity=1,
+ Str=<SP(SU)>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [20] 141 10}]
+g1
+  = \ (ds [Dmd=SP(SU)] :: Int) ->
+      case ds of { GHC.Types.I# ds [Dmd=SU] ->
+      case ds of ds {
+        __DEFAULT ->
+          (GHC.Types.I# (GHC.Prim.*# 2# ds),
+           case ds of wild {
+             __DEFAULT ->
+               case GHC.Classes.divInt# 2# wild of ww4 { __DEFAULT ->
+               GHC.Types.I# ww4
+               };
+             -1# -> GHC.Types.I# -2#;
+             0# -> case GHC.Real.divZeroError of wild [Dmd=B] { }
+           });
+        1# -> lvl
+      }
+      }
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 0#
+
+-- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
+lvl :: (Int, Int)
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False,
+         WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 30 0}]
+lvl = g1 (GHC.Types.I# 2#)
+
+-- RHS size: {terms: 28, types: 18, coercions: 0, joins: 0/0}
+h1 :: Int -> Int
+[LclIdX,
+ Arity=1,
+ Str=<SP(MU)>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [20] 111 10}]
+h1
+  = \ (ds [Dmd=SP(MU)] :: Int) ->
+      case ds of wild [Dmd=1P(1U)] { GHC.Types.I# ds [Dmd=MU] ->
+      case ds of {
+        __DEFAULT ->
+          case g1 wild of { (x [Dmd=SP(U)], ds [Dmd=SP(U)]) ->
+          case x of { GHC.Types.I# x ->
+          case ds of { GHC.Types.I# y -> GHC.Types.I# (GHC.Prim.+# x y) }
+          }
+          };
+        1# -> lvl;
+        2# -> case lvl of { (ds1 [Dmd=A], y [Dmd=SU]) -> y }
+      }
+      }
+
+
+
+
+==================== Demand analysis ====================
+Result size of Demand analysis
+  = {terms: 171, types: 120, coercions: 0, joins: 0/0}
+
+-- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Prim.Addr#
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 20 0}]
+$trModule = "main"#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Types.TrName
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+$trModule = GHC.Types.TrNameS $trModule
+
+-- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Prim.Addr#
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 30 0}]
+$trModule = "T18894"#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+$trModule :: GHC.Types.TrName
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+$trModule = GHC.Types.TrNameS $trModule
+
+-- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
+T18894.$trModule :: GHC.Types.Module
+[LclIdX,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+T18894.$trModule = GHC.Types.Module $trModule $trModule
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 0#
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# -2#
+
+-- RHS size: {terms: 32, types: 18, coercions: 0, joins: 0/0}
+$wg2 [InlPrag=NOINLINE, Dmd=UCU(CS(P(1P(U),SP(U))))]
+  :: Int -> GHC.Prim.Int# -> (# Int, Int #)
+[LclId,
+ Arity=2,
+ Str=<UP(U)><SU>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [20 30] 121 20}]
+$wg2
+  = \ (w [Dmd=UP(U)] :: Int) (ww [Dmd=SU] :: GHC.Prim.Int#) ->
+      case ww of ds {
+        __DEFAULT ->
+          (# case w of { GHC.Types.I# y -> GHC.Types.I# (GHC.Prim.*# 2# y) },
+             case ds of {
+               __DEFAULT ->
+                 case GHC.Classes.divInt# 2# ds of ww4 { __DEFAULT ->
+                 GHC.Types.I# ww4
+                 };
+               -1# -> lvl;
+               0# -> case GHC.Real.divZeroError of wild [Dmd=B] { }
+             } #);
+        1# -> (# w, lvl #)
+      }
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 2#
+
+-- RHS size: {terms: 34, types: 21, coercions: 0, joins: 0/0}
+$wh2 [InlPrag=[2]] :: GHC.Prim.Int# -> Int
+[LclId,
+ Arity=1,
+ Str=<SU>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [30] 162 10}]
+$wh2
+  = \ (ww [Dmd=SU] :: GHC.Prim.Int#) ->
+      case ww of ds {
+        __DEFAULT ->
+          case GHC.Prim.remInt# ds 2# of {
+            __DEFAULT ->
+              case $wg2 (GHC.Types.I# ds) 2# of
+              { (# ww [Dmd=A], ww [Dmd=SU] #) ->
+              ww
+              };
+            0# ->
+              case $wg2 lvl ds of { (# ww [Dmd=SP(U)], ww [Dmd=SP(U)] #) ->
+              case ww of { GHC.Types.I# x ->
+              case ww of { GHC.Types.I# y -> GHC.Types.I# (GHC.Prim.+# x y) }
+              }
+              }
+          };
+        1# -> lvl
+      }
+
+-- RHS size: {terms: 6, types: 3, coercions: 0, joins: 0/0}
+h2 [InlPrag=[2]] :: Int -> Int
+[LclIdX,
+ Arity=1,
+ Str=<SP(SU)>,
+ 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, Dmd=MU] -> $wh2 ww }}]
+h2
+  = \ (w [Dmd=SP(SU)] :: Int) ->
+      case w of { GHC.Types.I# ww [Dmd=SU] -> $wh2 ww }
+
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+lvl :: Int
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 10}]
+lvl = GHC.Types.I# 15#
+
+-- RHS size: {terms: 28, types: 15, coercions: 0, joins: 0/0}
+$wg1 [InlPrag=NOINLINE, Dmd=UCU(P(UP(U),UP(U)))]
+  :: GHC.Prim.Int# -> (# Int, Int #)
+[LclId,
+ Arity=1,
+ Str=<SU>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [30] 111 20}]
+$wg1
+  = \ (ww [Dmd=SU] :: GHC.Prim.Int#) ->
+      case ww of ds {
+        __DEFAULT ->
+          (# GHC.Types.I# (GHC.Prim.*# 2# ds),
+             case ds of {
+               __DEFAULT ->
+                 case GHC.Classes.divInt# 2# ds of ww4 { __DEFAULT ->
+                 GHC.Types.I# ww4
+                 };
+               -1# -> lvl;
+               0# -> case GHC.Real.divZeroError of wild [Dmd=B] { }
+             } #);
+        1# -> (# lvl, lvl #)
+      }
+
+-- RHS size: {terms: 7, types: 9, coercions: 0, joins: 0/0}
+lvl :: (Int, Int)
+[LclId,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False,
+         WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 40 10}]
+lvl = case $wg1 2# of { (# ww, ww #) -> (ww, ww) }
+
+-- RHS size: {terms: 25, types: 18, coercions: 0, joins: 0/0}
+$wh1 [InlPrag=[2]] :: GHC.Prim.Int# -> Int
+[LclId,
+ Arity=1,
+ Str=<SU>,
+ Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [50] 101 10}]
+$wh1
+  = \ (ww [Dmd=SU] :: GHC.Prim.Int#) ->
+      case ww of ds [Dmd=1U] {
+        __DEFAULT ->
+          case $wg1 ds of { (# ww [Dmd=SP(U)], ww [Dmd=SP(U)] #) ->
+          case ww of { GHC.Types.I# x ->
+          case ww of { GHC.Types.I# y -> GHC.Types.I# (GHC.Prim.+# x y) }
+          }
+          };
+        1# -> lvl;
+        2# -> case lvl of { (ds1 [Dmd=A], y [Dmd=SU]) -> y }
+      }
+
+-- RHS size: {terms: 6, types: 3, coercions: 0, joins: 0/0}
+h1 [InlPrag=[2]] :: Int -> Int
+[LclIdX,
+ Arity=1,
+ Str=<SP(SU)>,
+ 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, Dmd=MU] -> $wh1 ww }}]
+h1
+  = \ (w [Dmd=SP(SU)] :: Int) ->
+      case w of { GHC.Types.I# ww [Dmd=SU] -> $wh1 ww }
+
+
+


=====================================
testsuite/tests/stranal/should_compile/all.T
=====================================
@@ -58,3 +58,5 @@ test('T18122',  [ grep_errmsg(r'wfoo =') ], compile, ['-ddump-simpl'])
 
 # We care about the call demand on $wg
 test('T18903',  [ grep_errmsg(r'Dmd=\S+C\S+') ], compile, ['-ddump-simpl -dsuppress-uniques'])
+# We care about the call demand on $wg1 and $wg2
+test('T18894',  [ grep_errmsg(r'Dmd=\S+C\S+') ], compile, ['-ddump-stranal -dsuppress-uniques'])


=====================================
testsuite/tests/stranal/sigs/T5075.stderr
=====================================
@@ -1,7 +1,7 @@
 
 ==================== Strictness signatures ====================
 T5075.$trModule:
-T5075.loop: <MP(A,A,MCM(CS(U)),A,A,A,A,A)><UP(A,A,UCU(CS(U)),A,A,A,UCU(U))><U>
+T5075.loop: <MP(A,A,MCM(CS(U)),A,A,A,A,A)><UP(A,A,UCU(CS(U)),A,A,A,U)><U>
 
 
 
@@ -13,6 +13,6 @@ T5075.loop:
 
 ==================== Strictness signatures ====================
 T5075.$trModule:
-T5075.loop: <SP(A,A,MCM(CS(U)),A,A,A,A,A)><UP(A,A,UCU(CS(U)),A,A,A,UCU(U))><U>
+T5075.loop: <SP(A,A,MCM(CS(U)),A,A,A,A,A)><UP(A,A,UCU(CS(U)),A,A,A,U)><U>
 
 



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/549af6957748293cd497ccbef421c30666b56f31...3a7344fb01f296a88e8136de47a81a5d2448d795

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/549af6957748293cd497ccbef421c30666b56f31...3a7344fb01f296a88e8136de47a81a5d2448d795
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