#3138: Returning a known constructor: GHC generates terrible code for cmonad
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Reporter: simonpj | Owner:
Type: run-time performance bug | Status: new
Priority: normal | Milestone: 6.12 branch
Component: Compiler | Version: 6.10.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: Unknown/Multiple |
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Comment (by simonpj):
Indeed GHC isn't a supercompiler and doesn't specialise recursive
functions for their call sites. As it happens, Peter Jonsson started
yesterday as an intern to try just that! But as of today, no. (Except
that, perhaps inconsistently, within a single module, we specialise
overloaded functions (including recursive ones) at the types where they
are called locally. You can use a SPECIALISE pragma to make that happen
for types where there is no local call.)
Even non-recursive functions are inlined only if they look small enough.
That can indeed lead to dictionaries being passed instead of code being
duplicated.
Meanwhile I'll look at the simpler example -- thanks.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3138#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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