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authorBen Gamari <ben@smart-cactus.org>2021-04-23 15:52:49 -0400
committerMarge Bot <ben+marge-bot@smart-cactus.org>2022-02-04 10:01:59 -0500
commiteddaa591a478e7598a9f5df4c26306e4fadbf08e (patch)
treecee39e050800167d85b1aaf75ceab7286a4a7bd1 /testsuite/tests/typecheck/should_fail/T5095.stderr
parent4e6780bb44f81f81a39b6b362eef855e68431882 (diff)
downloadhaskell-eddaa591a478e7598a9f5df4c26306e4fadbf08e.tar.gz
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>
Diffstat (limited to 'testsuite/tests/typecheck/should_fail/T5095.stderr')
-rw-r--r--testsuite/tests/typecheck/should_fail/T5095.stderr6
1 files changed, 3 insertions, 3 deletions
diff --git a/testsuite/tests/typecheck/should_fail/T5095.stderr b/testsuite/tests/typecheck/should_fail/T5095.stderr
index 27784f8250..083551cc5f 100644
--- a/testsuite/tests/typecheck/should_fail/T5095.stderr
+++ b/testsuite/tests/typecheck/should_fail/T5095.stderr
@@ -5,9 +5,9 @@ T5095.hs:9:11: error:
instance [overlappable] Show a => Eq a -- Defined at T5095.hs:5:31
Potentially matching instances:
instance Eq Ordering -- Defined in ‘GHC.Classes’
- instance Eq a => Eq (Maybe a) -- Defined in ‘GHC.Maybe’
- ...plus 24 others
- ...plus six instances involving out-of-scope types
+ instance Eq Integer -- Defined in ‘GHC.Num.Integer’
+ ...plus 23 others
+ ...plus four instances involving out-of-scope types
(use -fprint-potential-instances to see them all)
(The choice depends on the instantiation of ‘a’
To pick the first instance above, use IncoherentInstances