Separate CPR analysis from the Demand analyserwip/sep-cpr

The reasons for that can be found in the wiki:
https://gitlab.haskell.org/ghc/ghc/wikis/nested-cpr/split-off-cpr

We now run CPR after demand analysis (except for after the final demand
analysis run just before code gen). CPR got its own dump flags
(`-ddump-cpr-anal`, `-ddump-cpr-signatures`), but not its own flag to
activate/deactivate. It will run with `-fstrictness`/`-fworker-wrapper`.

As explained on the wiki page, this step is necessary for a sane Nested
CPR analysis. And it has quite positive impact on compiler performance:

Metric Decrease:
    T9233
    T9675
    T9961
    T15263

2 files changed, 17 insertions, 2 deletions

diff --git a/compiler/GHC/Iface/Syntax.hs b/compiler/GHC/Iface/Syntax.hs
index 9509cfe77c..45751424d6 100644
--- a/compiler/GHC/Iface/Syntax.hs
+++ b/compiler/GHC/Iface/Syntax.hs
@@ -49,6 +49,7 @@ import BinFingerprint
 import CoreSyn( IsOrphan, isOrphan )
 import DynFlags( gopt, GeneralFlag (Opt_PrintAxiomIncomps) )
 import Demand
+import Cpr
 import Class
 import FieldLabel
 import NameSet
@@ -344,6 +345,7 @@ data IfaceIdInfo
 data IfaceInfoItem
   = HsArity         Arity
   | HsStrictness    StrictSig
+  | HsCpr           CprSig
   | HsInline        InlinePragma
   | HsUnfold        Bool             -- True <=> isStrongLoopBreaker is true
                     IfaceUnfolding   -- See Note [Expose recursive functions]
@@ -1394,7 +1396,8 @@ instance Outputable IfaceInfoItem where
                               <> colon <+> ppr unf
   ppr (HsInline prag)       = text "Inline:" <+> ppr prag
   ppr (HsArity arity)       = text "Arity:" <+> int arity
-  ppr (HsStrictness str) = text "Strictness:" <+> pprIfaceStrictSig str
+  ppr (HsStrictness str)    = text "Strictness:" <+> pprIfaceStrictSig str
+  ppr (HsCpr cpr)           = text "CPR:" <+> ppr cpr
   ppr HsNoCafRefs           = text "HasNoCafRefs"
   ppr HsLevity              = text "Never levity-polymorphic"
 
@@ -2168,6 +2171,7 @@ instance Binary IfaceInfoItem where
     put_ bh (HsInline ad)         = putByte bh 3 >> put_ bh ad
     put_ bh HsNoCafRefs           = putByte bh 4
     put_ bh HsLevity              = putByte bh 5
+    put_ bh (HsCpr cpr)           = putByte bh 6 >> put_ bh cpr
     get bh = do
         h <- getByte bh
         case h of
@@ -2178,7 +2182,8 @@ instance Binary IfaceInfoItem where
                     return (HsUnfold lb ad)
             3 -> liftM HsInline $ get bh
             4 -> return HsNoCafRefs
-            _ -> return HsLevity
+            5 -> return HsLevity
+            _ -> HsCpr <$> get bh
 
 instance Binary IfaceUnfolding where
     put_ bh (IfCoreUnfold s e) = do
@@ -2513,6 +2518,7 @@ instance NFData IfaceInfoItem where
     HsUnfold b unf -> rnf b `seq` rnf unf
     HsNoCafRefs -> ()
     HsLevity -> ()
+    HsCpr cpr -> cpr `seq` ()
 
 instance NFData IfaceUnfolding where
   rnf = \case
diff --git a/compiler/GHC/Iface/Tidy.hs b/compiler/GHC/Iface/Tidy.hs
index 8da7700e0e..2b1a4b7108 100644
--- a/compiler/GHC/Iface/Tidy.hs
+++ b/compiler/GHC/Iface/Tidy.hs
@@ -40,6 +40,7 @@ import IdInfo
 import InstEnv
 import Type             ( tidyTopType )
 import Demand           ( appIsBottom, isTopSig, isBottomingSig )
+import Cpr              ( mkCprSig, botCpr )
 import BasicTypes
 import Name hiding (varName)
 import NameSet
@@ -1150,6 +1151,7 @@ tidyTopIdInfo dflags rhs_tidy_env name orig_rhs tidy_rhs idinfo show_unfold
                         --      c.f. CoreTidy.tidyLetBndr
         `setArityInfo`      arity
         `setStrictnessInfo` final_sig
+        `setCprInfo`        final_cpr
         `setUnfoldingInfo`  minimal_unfold_info  -- See note [Preserve evaluatedness]
                                                  -- in CoreTidy
 
@@ -1157,6 +1159,7 @@ tidyTopIdInfo dflags rhs_tidy_env name orig_rhs tidy_rhs idinfo show_unfold
   = vanillaIdInfo
         `setArityInfo`         arity
         `setStrictnessInfo`    final_sig
+        `setCprInfo`           final_cpr
         `setOccInfo`           robust_occ_info
         `setInlinePragInfo`    (inlinePragInfo idinfo)
         `setUnfoldingInfo`     unfold_info
@@ -1180,6 +1183,12 @@ tidyTopIdInfo dflags rhs_tidy_env name orig_rhs tidy_rhs idinfo show_unfold
               | Just (_, nsig) <- mb_bot_str = nsig
               | otherwise                    = sig
 
+    cpr = cprInfo idinfo
+    final_cpr | Just _ <- mb_bot_str
+              = mkCprSig arity botCpr
+              | otherwise
+              = cpr
+
     _bottom_hidden id_sig = case mb_bot_str of
                                   Nothing         -> False
                                   Just (arity, _) -> not (appIsBottom id_sig arity)