compiler: Introduce and use RoughMap for instance environments

Here we introduce a new data structure, RoughMap, inspired by the
previous `RoughTc` matching mechanism for checking instance matches.
This allows [Fam]InstEnv to be implemented as a trie indexed by these
RoughTc signatures, reducing the complexity of instance lookup and
FamInstEnv merging (done during the family instance conflict test)
from O(n) to O(log n).

The critical performance improvement currently realised by this patch is
in instance matching. In particular the RoughMap mechanism allows us to
discount many potential instances which will never match for constraints
involving type variables (see Note [Matching a RoughMap]). In realistic
code bases matchInstEnv was accounting for 50% of typechecker time due
to redundant work checking instances when simplifying instance contexts
when deriving instances. With this patch the cost is significantly
reduced.

The larger constants in InstEnv creation do mean that a few small
tests regress in allocations slightly. However, the runtime of T19703 is
reduced by a factor of 4. Moreover, the compilation time of the Cabal
library is slightly improved.

A couple of test cases are included which demonstrate significant
improvements in compile time with this patch.

This unfortunately does not fix the testcase provided in #19703 but does
fix #20933

-------------------------
Metric Decrease:
    T12425
Metric Increase:
    T13719
    T9872a
    T9872d
    hard_hole_fits
-------------------------

Co-authored-by: Matthew Pickering <matthewtpickering@gmail.com>

2 files changed, 23 insertions, 0 deletions

diff --git a/compiler/GHC/Types/Name/Env.hs b/compiler/GHC/Types/Name/Env.hs
index 6394c986d5..a65bbed4a2 100644
--- a/compiler/GHC/Types/Name/Env.hs
+++ b/compiler/GHC/Types/Name/Env.hs
@@ -28,11 +28,15 @@ module GHC.Types.Name.Env (
         DNameEnv,
 
         emptyDNameEnv,
+        isEmptyDNameEnv,
         lookupDNameEnv,
         delFromDNameEnv, filterDNameEnv,
         mapDNameEnv,
         adjustDNameEnv, alterDNameEnv, extendDNameEnv,
         eltsDNameEnv, extendDNameEnv_C,
+        plusDNameEnv_C,
+        foldDNameEnv,
+        nonDetStrictFoldDNameEnv,
         -- ** Dependency analysis
         depAnal
     ) where
@@ -160,6 +164,9 @@ type DNameEnv a = UniqDFM Name a
 emptyDNameEnv :: DNameEnv a
 emptyDNameEnv = emptyUDFM
 
+isEmptyDNameEnv :: DNameEnv a -> Bool
+isEmptyDNameEnv = isNullUDFM
+
 lookupDNameEnv :: DNameEnv a -> Name -> Maybe a
 lookupDNameEnv = lookupUDFM
 
@@ -186,3 +193,13 @@ extendDNameEnv_C = addToUDFM_C
 
 eltsDNameEnv :: DNameEnv a -> [a]
 eltsDNameEnv = eltsUDFM
+
+foldDNameEnv :: (a -> b -> b) -> b -> DNameEnv a -> b
+foldDNameEnv = foldUDFM
+
+plusDNameEnv_C :: (elt -> elt -> elt) -> DNameEnv elt -> DNameEnv elt -> DNameEnv elt
+plusDNameEnv_C = plusUDFM_C
+
+nonDetStrictFoldDNameEnv :: (a -> b -> b) -> b -> DNameEnv a -> b
+nonDetStrictFoldDNameEnv = nonDetStrictFoldUDFM
+
diff --git a/compiler/GHC/Types/Unique/FM.hs b/compiler/GHC/Types/Unique/FM.hs
index 265345e2ec..8f96731599 100644
--- a/compiler/GHC/Types/Unique/FM.hs
+++ b/compiler/GHC/Types/Unique/FM.hs
@@ -65,6 +65,7 @@ module GHC.Types.Unique.FM (
         disjointUFM,
         equalKeysUFM,
         nonDetStrictFoldUFM, foldUFM, nonDetStrictFoldUFM_DirectlyM,
+        nonDetStrictFoldUFM_Directly,
         anyUFM, allUFM, seqEltsUFM,
         mapUFM, mapUFM_Directly,
         mapMaybeUFM,
@@ -411,6 +412,7 @@ nonDetKeysUFM (UFM m) = map getUnique $ M.keys m
 -- nondeterminism.
 nonDetStrictFoldUFM :: (elt -> a -> a) -> a -> UniqFM key elt -> a
 nonDetStrictFoldUFM k z (UFM m) = M.foldl' (flip k) z m
+{-# INLINE nonDetStrictFoldUFM #-}
 
 -- | In essence foldM
 -- See Note [Deterministic UniqFM] to learn about nondeterminism.
@@ -423,6 +425,10 @@ nonDetStrictFoldUFM_DirectlyM f z0 (UFM xs) = M.foldrWithKey c return xs z0
   where c u x k z = f (getUnique u) z x >>= k
         {-# INLINE c #-}
 
+nonDetStrictFoldUFM_Directly:: (Unique -> elt -> a -> a) -> a -> UniqFM key elt -> a
+nonDetStrictFoldUFM_Directly k z (UFM m) = M.foldlWithKey' (\z' i x -> k (getUnique i) x z') z m
+{-# INLINE nonDetStrictFoldUFM_Directly #-}
+
 -- See Note [Deterministic UniqFM] to learn about nondeterminism.
 -- If you use this please provide a justification why it doesn't introduce
 -- nondeterminism.