Re-engineer caseRules to add tagToEnum/dataToTag

See Note [Scrutinee Constant Folding] in SimplUtils

* Add cases for tagToEnum and dataToTag. This is the main new
  bit.  It allows the simplifier to remove the pervasive uses
  of     case tagToEnum (a > b) of
            False -> e1
            True  -> e2
  and replace it by the simpler
         case a > b of
            DEFAULT -> e1
            1#      -> e2
  See Note [caseRules for tagToEnum]
  and Note [caseRules for dataToTag] in PrelRules.

* This required some changes to the API of caseRules, and hence
  to code in SimplUtils.  See Note [Scrutinee Constant Folding]
  in SimplUtils.

* Avoid duplication of work in the (unusual) case of
     case BIG + 3# of b
       DEFAULT -> e1
       6#      -> e2

  Previously we got
     case BIG of
       DEFAULT -> let b = BIG + 3# in e1
       3#      -> let b = 6#       in e2

  Now we get
     case BIG of b#
       DEFAULT -> let b = b' + 3# in e1
       3#      -> let b = 6#      in e2

* Avoid duplicated code in caseRules

A knock-on refactoring:

* Move Note [Word/Int underflow/overflow] to Literal, as
  documentation to accompany mkMachIntWrap etc; and get
  rid of PrelRuls.intResult' in favour of mkMachIntWrap

3 files changed, 96 insertions, 96 deletions

diff --git a/testsuite/tests/simplCore/should_compile/T3772.stdout b/testsuite/tests/simplCore/should_compile/T3772.stdout
index 44aee7b69e..a4ab97da38 100644
--- a/testsuite/tests/simplCore/should_compile/T3772.stdout
+++ b/testsuite/tests/simplCore/should_compile/T3772.stdout
@@ -1,7 +1,7 @@
 
 ==================== Tidy Core ====================
 Result size of Tidy Core
-  = {terms: 44, types: 19, coercions: 0, joins: 0/0}
+  = {terms: 43, types: 18, coercions: 0, joins: 0/0}
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 T3772.$trModule4 :: GHC.Prim.Addr#
@@ -59,14 +59,14 @@ $wxs
       }
 end Rec }
 
--- RHS size: {terms: 11, types: 3, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 10, types: 2, coercions: 0, joins: 0/0}
 T3772.$wfoo [InlPrag=NOINLINE] :: GHC.Prim.Int# -> ()
 [GblId, Arity=1, Caf=NoCafRefs, Str=<S,U>]
 T3772.$wfoo
   = \ (ww :: GHC.Prim.Int#) ->
-      case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<# 0# ww) of {
-        False -> GHC.Tuple.();
-        True -> $wxs ww
+      case GHC.Prim.<# 0# ww of {
+        __DEFAULT -> GHC.Tuple.();
+        1# -> $wxs ww
       }
 
 -- RHS size: {terms: 6, types: 3, coercions: 0, joins: 0/0}
diff --git a/testsuite/tests/simplCore/should_compile/T4930.stderr b/testsuite/tests/simplCore/should_compile/T4930.stderr
index 9db97a5e1f..4d569485b3 100644
--- a/testsuite/tests/simplCore/should_compile/T4930.stderr
+++ b/testsuite/tests/simplCore/should_compile/T4930.stderr
@@ -1,7 +1,7 @@
 
 ==================== Tidy Core ====================
 Result size of Tidy Core
-  = {terms: 44, types: 17, coercions: 0, joins: 0/0}
+  = {terms: 43, types: 16, coercions: 0, joins: 0/0}
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 T4930.$trModule4 :: GHC.Prim.Addr#
@@ -44,20 +44,20 @@ T4930.$trModule :: GHC.Types.Module
  Str=m,
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 30}]
-T4930.$trModule =
-  GHC.Types.Module T4930.$trModule3 T4930.$trModule1
+T4930.$trModule
+  = GHC.Types.Module T4930.$trModule3 T4930.$trModule1
 
 Rec {
--- RHS size: {terms: 18, types: 4, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 17, types: 3, coercions: 0, joins: 0/0}
 T4930.$wfoo [InlPrag=[0], Occ=LoopBreaker]
   :: GHC.Prim.Int# -> GHC.Prim.Int#
 [GblId, Arity=1, Caf=NoCafRefs, Str=<S,U>]
-T4930.$wfoo =
-  \ (ww :: GHC.Prim.Int#) ->
-    case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<# ww 5#) of {
-      False -> GHC.Prim.+# ww 5#;
-      True -> case T4930.$wfoo ww of { __DEFAULT -> GHC.Prim.+# ww 5# }
-    }
+T4930.$wfoo
+  = \ (ww :: GHC.Prim.Int#) ->
+      case GHC.Prim.<# ww 5# of {
+        __DEFAULT -> GHC.Prim.+# ww 5#;
+        1# -> case T4930.$wfoo ww of { __DEFAULT -> GHC.Prim.+# ww 5# }
+      }
 end Rec }
 
 -- RHS size: {terms: 10, types: 4, coercions: 0, joins: 0/0}
@@ -73,11 +73,11 @@ foo [InlPrag=INLINE[0]] :: Int -> Int
                  case w of { GHC.Types.I# ww1 [Occ=Once] ->
                  case T4930.$wfoo ww1 of ww2 { __DEFAULT -> GHC.Types.I# ww2 }
                  }}]
-foo =
-  \ (w :: Int) ->
-    case w of { GHC.Types.I# ww1 ->
-    case T4930.$wfoo ww1 of ww2 { __DEFAULT -> GHC.Types.I# ww2 }
-    }
+foo
+  = \ (w :: Int) ->
+      case w of { GHC.Types.I# ww1 ->
+      case T4930.$wfoo ww1 of ww2 { __DEFAULT -> GHC.Types.I# ww2 }
+      }
 
 
 
diff --git a/testsuite/tests/simplCore/should_compile/spec-inline.stderr b/testsuite/tests/simplCore/should_compile/spec-inline.stderr
index dda28c8926..53b315dc9c 100644
--- a/testsuite/tests/simplCore/should_compile/spec-inline.stderr
+++ b/testsuite/tests/simplCore/should_compile/spec-inline.stderr
@@ -1,7 +1,7 @@
 
 ==================== Tidy Core ====================
 Result size of Tidy Core
-  = {terms: 178, types: 68, coercions: 0, joins: 0/2}
+  = {terms: 172, types: 62, coercions: 0, joins: 0/2}
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 Roman.$trModule4 :: GHC.Prim.Addr#
@@ -44,8 +44,8 @@ Roman.$trModule :: GHC.Types.Module
  Str=m,
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 30}]
-Roman.$trModule =
-  GHC.Types.Module Roman.$trModule3 Roman.$trModule1
+Roman.$trModule
+  = GHC.Types.Module Roman.$trModule3 Roman.$trModule1
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 lvl :: GHC.Prim.Addr#
@@ -55,83 +55,83 @@ lvl = "spec-inline.hs:(19,5)-(29,25)|function go"#
 -- RHS size: {terms: 2, types: 2, coercions: 0, joins: 0/0}
 Roman.foo3 :: Int
 [GblId, Str=x]
-Roman.foo3 =
-  Control.Exception.Base.patError @ 'GHC.Types.LiftedRep @ Int lvl
+Roman.foo3
+  = Control.Exception.Base.patError @ 'GHC.Types.LiftedRep @ Int lvl
 
 Rec {
--- RHS size: {terms: 55, types: 9, coercions: 0, joins: 0/1}
+-- RHS size: {terms: 52, types: 6, coercions: 0, joins: 0/1}
 Roman.foo_$s$wgo [Occ=LoopBreaker]
   :: GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.Int#
 [GblId, Arity=2, Caf=NoCafRefs, Str=<S,U><S,U>]
-Roman.foo_$s$wgo =
-  \ (sc :: GHC.Prim.Int#) (sc1 :: GHC.Prim.Int#) ->
-    let {
-      m :: GHC.Prim.Int#
-      [LclId]
-      m =
-        GHC.Prim.+#
-          (GHC.Prim.+#
-             (GHC.Prim.+#
-                (GHC.Prim.+# (GHC.Prim.+# (GHC.Prim.+# sc sc) sc) sc) sc)
-             sc)
-          sc } in
-    case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<=# sc1 0#) of {
-      False ->
-        case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<# sc1 100#) of {
-          False ->
-            case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<# sc1 500#) of {
-              False -> Roman.foo_$s$wgo (GHC.Prim.+# m m) (GHC.Prim.-# sc1 1#);
-              True -> Roman.foo_$s$wgo m (GHC.Prim.-# sc1 3#)
-            };
-          True -> Roman.foo_$s$wgo sc (GHC.Prim.-# sc1 2#)
-        };
-      True -> 0#
-    }
+Roman.foo_$s$wgo
+  = \ (sc :: GHC.Prim.Int#) (sc1 :: GHC.Prim.Int#) ->
+      let {
+        m :: GHC.Prim.Int#
+        [LclId]
+        m = GHC.Prim.+#
+              (GHC.Prim.+#
+                 (GHC.Prim.+#
+                    (GHC.Prim.+# (GHC.Prim.+# (GHC.Prim.+# sc sc) sc) sc) sc)
+                 sc)
+              sc } in
+      case GHC.Prim.<=# sc1 0# of {
+        __DEFAULT ->
+          case GHC.Prim.<# sc1 100# of {
+            __DEFAULT ->
+              case GHC.Prim.<# sc1 500# of {
+                __DEFAULT ->
+                  Roman.foo_$s$wgo (GHC.Prim.+# m m) (GHC.Prim.-# sc1 1#);
+                1# -> Roman.foo_$s$wgo m (GHC.Prim.-# sc1 3#)
+              };
+            1# -> Roman.foo_$s$wgo sc (GHC.Prim.-# sc1 2#)
+          };
+        1# -> 0#
+      }
 end Rec }
 
--- RHS size: {terms: 74, types: 22, coercions: 0, joins: 0/1}
+-- RHS size: {terms: 71, types: 19, coercions: 0, joins: 0/1}
 Roman.$wgo [InlPrag=[0]] :: Maybe Int -> Maybe Int -> GHC.Prim.Int#
 [GblId,
  Arity=2,
  Str=<S,1*U><S,1*U>,
  Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
-         WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 30] 256 0}]
-Roman.$wgo =
-  \ (w :: Maybe Int) (w1 :: Maybe Int) ->
-    case w1 of {
-      Nothing -> case Roman.foo3 of wild1 { };
-      Just x ->
-        case x of { GHC.Types.I# ipv ->
-        let {
-          m :: GHC.Prim.Int#
-          [LclId]
-          m =
-            GHC.Prim.+#
-              (GHC.Prim.+#
-                 (GHC.Prim.+#
-                    (GHC.Prim.+# (GHC.Prim.+# (GHC.Prim.+# ipv ipv) ipv) ipv) ipv)
-                 ipv)
-              ipv } in
-        case w of {
-          Nothing -> Roman.foo_$s$wgo m 10#;
-          Just n ->
-            case n of { GHC.Types.I# x2 ->
-            case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<=# x2 0#) of {
-              False ->
-                case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<# x2 100#) of {
-                  False ->
-                    case GHC.Prim.tagToEnum# @ Bool (GHC.Prim.<# x2 500#) of {
-                      False -> Roman.foo_$s$wgo (GHC.Prim.+# m m) (GHC.Prim.-# x2 1#);
-                      True -> Roman.foo_$s$wgo m (GHC.Prim.-# x2 3#)
-                    };
-                  True -> Roman.foo_$s$wgo ipv (GHC.Prim.-# x2 2#)
-                };
-              True -> 0#
-            }
-            }
-        }
-        }
-    }
+         WorkFree=True, Expandable=True, Guidance=IF_ARGS [60 30] 253 0}]
+Roman.$wgo
+  = \ (w :: Maybe Int) (w1 :: Maybe Int) ->
+      case w1 of {
+        Nothing -> case Roman.foo3 of wild1 { };
+        Just x ->
+          case x of { GHC.Types.I# ipv ->
+          let {
+            m :: GHC.Prim.Int#
+            [LclId]
+            m = GHC.Prim.+#
+                  (GHC.Prim.+#
+                     (GHC.Prim.+#
+                        (GHC.Prim.+# (GHC.Prim.+# (GHC.Prim.+# ipv ipv) ipv) ipv) ipv)
+                     ipv)
+                  ipv } in
+          case w of {
+            Nothing -> Roman.foo_$s$wgo m 10#;
+            Just n ->
+              case n of { GHC.Types.I# x2 ->
+              case GHC.Prim.<=# x2 0# of {
+                __DEFAULT ->
+                  case GHC.Prim.<# x2 100# of {
+                    __DEFAULT ->
+                      case GHC.Prim.<# x2 500# of {
+                        __DEFAULT ->
+                          Roman.foo_$s$wgo (GHC.Prim.+# m m) (GHC.Prim.-# x2 1#);
+                        1# -> Roman.foo_$s$wgo m (GHC.Prim.-# x2 3#)
+                      };
+                    1# -> Roman.foo_$s$wgo ipv (GHC.Prim.-# x2 2#)
+                  };
+                1# -> 0#
+              }
+              }
+          }
+          }
+      }
 
 -- RHS size: {terms: 9, types: 5, coercions: 0, joins: 0/0}
 Roman.foo_go [InlPrag=INLINE[0]] :: Maybe Int -> Maybe Int -> Int
@@ -143,9 +143,9 @@ Roman.foo_go [InlPrag=INLINE[0]] :: Maybe Int -> Maybe Int -> Int
          Guidance=ALWAYS_IF(arity=2,unsat_ok=True,boring_ok=False)
          Tmpl= \ (w [Occ=Once] :: Maybe Int) (w1 [Occ=Once] :: Maybe Int) ->
                  case Roman.$wgo w w1 of ww { __DEFAULT -> GHC.Types.I# ww }}]
-Roman.foo_go =
-  \ (w :: Maybe Int) (w1 :: Maybe Int) ->
-    case Roman.$wgo w w1 of ww { __DEFAULT -> GHC.Types.I# ww }
+Roman.foo_go
+  = \ (w :: Maybe Int) (w1 :: Maybe Int) ->
+      case Roman.$wgo w w1 of ww { __DEFAULT -> GHC.Types.I# ww }
 
 -- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
 Roman.foo2 :: Int
@@ -178,11 +178,11 @@ foo :: Int -> Int
                  case n of n1 { GHC.Types.I# _ [Occ=Dead] ->
                  Roman.foo_go (GHC.Base.Just @ Int n1) Roman.foo1
                  }}]
-foo =
-  \ (n :: Int) ->
-    case n of { GHC.Types.I# ipv ->
-    case Roman.foo_$s$wgo 6# ipv of ww { __DEFAULT -> GHC.Types.I# ww }
-    }
+foo
+  = \ (n :: Int) ->
+      case n of { GHC.Types.I# ipv ->
+      case Roman.foo_$s$wgo 6# ipv of ww { __DEFAULT -> GHC.Types.I# ww }
+      }
 
 
 ------ Local rules for imported ids --------