TcTypeable: Try to reuse KindReps

Here we rework the TcTypeable implementation to reuse KindRep bindings
when possible. This is an attempt at minimizing the impact of Typeable
binding generation by reducing the number of bindings that we produce.

It turns out that this produces some pretty reasonable compiler
allocations improvements. It seems to erase most of the increases
initially introduced by TTypeable in the testsuite. Moreover, nofib
shows,
```
        -1 s.d.                -----          -3.555%
        +1 s.d.                -----          +1.937%
        Average                -----          -0.847%
```

Here are a few of the high-scorers (ignore last column, which is for
D3219),
```
veritas
          Types             88800920         -18.945%         -21.480%

veritas
        Tactics            540766744         -27.256%         -27.338%

sched
           Main            567013384          -4.947%          -5.358%

listcompr
           Main            532300000          -4.273%          -4.572%

listcopy
           Main            537785392          -4.382%          -4.635%

anna
       BaseDefs           1984225032         -10.639%         -10.832%

```
as expected, these tend to be modules with either very many or very
large types.

Test Plan: Validate

Reviewers: austin, dfeuer

Subscribers: simonmar, dfeuer, thomie

Differential Revision: https://phabricator.haskell.org/D3166

1 files changed, 16 insertions, 31 deletions

diff --git a/testsuite/tests/deSugar/should_compile/T2431.stderr b/testsuite/tests/deSugar/should_compile/T2431.stderr
index 2993e15d95..1fd5b44d86 100644
--- a/testsuite/tests/deSugar/should_compile/T2431.stderr
+++ b/testsuite/tests/deSugar/should_compile/T2431.stderr
@@ -1,7 +1,7 @@
 
 ==================== Tidy Core ====================
 Result size of Tidy Core
-  = {terms: 83, types: 49, coercions: 1, joins: 0/0}
+  = {terms: 74, types: 46, coercions: 1, joins: 0/0}
 
 -- RHS size: {terms: 2, types: 4, coercions: 1, joins: 0/0}
 T2431.$WRefl [InlPrag=INLINE[2]] :: forall a. a :~: a
@@ -52,25 +52,20 @@ $krep :: GHC.Types.KindRep
 [GblId, Caf=NoCafRefs]
 $krep = GHC.Types.KindRepTYPE GHC.Types.LiftedRep
 
--- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
 $krep1 :: GHC.Types.KindRep
 [GblId, Caf=NoCafRefs]
-$krep1 = GHC.Types.KindRepTYPE GHC.Types.LiftedRep
+$krep1 = GHC.Types.KindRepFun $krep $krep
 
--- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
 $krep2 :: GHC.Types.KindRep
 [GblId, Caf=NoCafRefs]
-$krep2 = GHC.Types.KindRepTYPE GHC.Types.LiftedRep
+$krep2 = GHC.Types.KindRepFun $krep $krep1
 
--- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
+-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
 $krep3 :: GHC.Types.KindRep
 [GblId, Caf=NoCafRefs]
-$krep3 = GHC.Types.KindRepFun $krep1 $krep2
-
--- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
-$krep4 :: GHC.Types.KindRep
-[GblId, Caf=NoCafRefs]
-$krep4 = GHC.Types.KindRepFun $krep $krep3
+$krep3 = GHC.Types.KindRepVar 0#
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 $tc:~:1 :: GHC.Prim.Addr#
@@ -92,34 +87,24 @@ T2431.$tc:~:
       T2431.$trModule
       $tc:~:2
       0#
-      $krep4
-
--- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
-$krep5 :: GHC.Types.KindRep
-[GblId, Caf=NoCafRefs]
-$krep5 = GHC.Types.KindRepVar 0#
-
--- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
-$krep6 :: GHC.Types.KindRep
-[GblId, Caf=NoCafRefs]
-$krep6 = GHC.Types.KindRepVar 0#
+      $krep2
 
 -- RHS size: {terms: 3, types: 2, coercions: 0, joins: 0/0}
-$krep7 :: [GHC.Types.KindRep]
+$krep4 :: [GHC.Types.KindRep]
 [GblId, Caf=NoCafRefs]
-$krep7
+$krep4
   = GHC.Types.:
-      @ GHC.Types.KindRep $krep6 (GHC.Types.[] @ GHC.Types.KindRep)
+      @ GHC.Types.KindRep $krep3 (GHC.Types.[] @ GHC.Types.KindRep)
 
 -- RHS size: {terms: 3, types: 1, coercions: 0, joins: 0/0}
-$krep8 :: [GHC.Types.KindRep]
+$krep5 :: [GHC.Types.KindRep]
 [GblId, Caf=NoCafRefs]
-$krep8 = GHC.Types.: @ GHC.Types.KindRep $krep5 $krep7
+$krep5 = GHC.Types.: @ GHC.Types.KindRep $krep3 $krep4
 
 -- RHS size: {terms: 3, types: 0, coercions: 0, joins: 0/0}
-$krep9 :: GHC.Types.KindRep
+$krep6 :: GHC.Types.KindRep
 [GblId, Caf=NoCafRefs]
-$krep9 = GHC.Types.KindRepTyConApp T2431.$tc:~: $krep8
+$krep6 = GHC.Types.KindRepTyConApp T2431.$tc:~: $krep5
 
 -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
 $tc'Refl1 :: GHC.Prim.Addr#
@@ -141,7 +126,7 @@ T2431.$tc'Refl
       T2431.$trModule
       $tc'Refl2
       1#
-      $krep9
+      $krep6