#5321: Very slow constraint solving for type families
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.4.1
Component: Compiler (Type checker) | Version: 7.0.3
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Compile-time
performance bug
Difficulty: Unknown | Testcase: perf/compiler/T5321Fun,
T5321FD
Blockedby: | Blocking:
Related: |
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Changes (by simonpj):
* testcase: => perf/compiler/T5321Fun, T5321FD
* difficulty: => Unknown
Comment:
I've just tried this with the HEAD (roughly 7.4). Here's what I get.
With functional dependencies:
{{{
testHMapFoo1 0.76sec 291Mbyte allocated
testHMapFoo2 0.41sec 161Mbyte allocated
testHMapFoo3 0.43sec 178Gbyte allocated
}}}
With type functions:
{{{
testHMapFoo1 0.71sec 297Mbyte allocated
testHMapFoo2 0.64sec 274Mbyte allocated
testHMapFoo3 0.65sec 274Gbyte allocated
}}}
I'm a bit surprised that the type-function version is slower. Dimitrios:
it might be worth profiling to see where the time is going.
But it's reassuring that the performance fragility wrt the order of
constraints seems to have gone away.
NB: this is without `-dcore-lint`, which makes a big difference because in
programs like this we get pretty big coercions.
I'm adding `T5321Fun` and `T5321FD` as performance tests. Currently all
tests are run with `-dcore-lint` on, so the performance numbers are much
worse than those above.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5321#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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