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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>
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I was working on making DynFlags stateless (#17957), especially by
storing loaded plugins into HscEnv instead of DynFlags. It turned out to
be complicated because HscEnv is in GHC.Driver.Types but LoadedPlugin
isn't: it is in GHC.Driver.Plugins which depends on GHC.Driver.Types. I
didn't feel like introducing yet another hs-boot file to break the loop.
Additionally I remember that while we introduced the module hierarchy
(#13009) we talked about splitting GHC.Driver.Types because it contained
various unrelated types and functions, but we never executed. I didn't
feel like making GHC.Driver.Types bigger with more unrelated Plugins
related types, so finally I bit the bullet and split GHC.Driver.Types.
As a consequence this patch moves a lot of things. I've tried to put
them into appropriate modules but nothing is set in stone.
Several other things moved to avoid loops.
* Removed Binary instances from GHC.Utils.Binary for random compiler
things
* Moved Typeable Binary instances into GHC.Utils.Binary.Typeable: they
import a lot of things that users of GHC.Utils.Binary don't want to
depend on.
* put everything related to Units/Modules under GHC.Unit:
GHC.Unit.Finder, GHC.Unit.Module.{ModGuts,ModIface,Deps,etc.}
* Created several modules under GHC.Types: GHC.Types.Fixity, SourceText,
etc.
* Split GHC.Utils.Error (into GHC.Types.Error)
* Finally removed GHC.Driver.Types
Note that this patch doesn't put loaded plugins into HscEnv. It's left
for another patch.
Bump haddock submodule
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