[GHC] #14790: eqTypeRep does not inline
GHC
ghc-devs at haskell.org
Mon Feb 12 14:44:49 UTC 2018
#14790: eqTypeRep does not inline
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Reporter: dfeuer | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.6.1
Component: Compiler | Version: 8.4.1-alpha2
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Runtime | Unknown/Multiple
performance bug | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by dfeuer):
No, not yet. I'll do that later today if you like. But I also don't really
understand what that will accomplish. `INLINABLE` tells GHC to make an
unfolding. But GHC already makes an unfolding; it just doesn't use it.
Does `INLINABLE` change what unfolding it makes? The purpose of the
wrapper is to use the fact that we know more about what information will
be available/useful at typical `eqTypeRep` call sites than the compiler
does; we therefore have a better sense of which part will actually be
useful to inline. If we inline the whole thing as it stands, then the call
site will get two calls to `typeRepFingerprint` and a call to `==`. That's
certainly larger than a call to `sameTypeRep`; is it also better in enough
cases to matter? I don't know. On the other hand, I know that in virtually
all realistic cases we want to use inlining to eliminate the `Maybe`
business.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14790#comment:14>
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