Improve optimisation of pattern synonym matching
Currently GHC does a very poor job of optimising pattern matches which include pattern synonyms.
It would be good to modify sameGroup
in compiler/deSugar/Match.hs
to be a lot smarter about when it is safe to group two pattern matches together.
Grouping was originally disabled as it is a bit trickier than originally thought. See #11224 (closed) for details.
The rule was originally to group two pattern matches together PgSyn p1
and PgSyn p2
when p1 == p2
. This rule wasn't safe when p1
had a polymorphic return type and thus could have a different type on each branch even though syntactically identical. A good solution to this ticket would come up with a smarter rule about when it is and isn't safe to group two together in the same spirit as the more complicated rules for view patterns.
Trac metadata
Trac field | Value |
---|---|
Version | 7.10.3 |
Type | Task |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |