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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2014-04-24 08:43:07 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2014-04-24 08:43:25 +0100 |
| commit | 79e46aea1643b4dfdc7c846bbefe06b83b535efd (patch) | |
| tree | 9ef1d1133f317063afe0a02ac21274534e43a715 /compiler/coreSyn | |
| parent | 134b722349b83c746f8f52f2dbd99b89d23b644c (diff) | |
| download | haskell-79e46aea1643b4dfdc7c846bbefe06b83b535efd.tar.gz | |
Don't eta-expand PAPs (fixes Trac #9020)
See Note [Do not eta-expand PAPs] in SimplUtils. This has a tremendously
good effect on compile times for some simple benchmarks.
The test is now where it belongs, in perf/compiler/T9020 (instead of simpl015).
I did a nofib run and got essentially zero change except for cacheprof which
gets 4% more allocation. I investigated. Turns out that we have
instance PP Reg where
pp ppm ST_0 = "%st"
pp ppm ST_1 = "%st(1)"
pp ppm ST_2 = "%st(2)"
pp ppm ST_3 = "%st(3)"
pp ppm ST_4 = "%st(4)"
pp ppm ST_5 = "%st(5)"
pp ppm ST_6 = "%st(6)"
pp ppm ST_7 = "%st(7)"
pp ppm r = "%" ++ map toLower (show r)
That (map toLower (show r) does a lot of map/toLowers. But if we inline show
we get something like
pp ppm ST_0 = "%st"
pp ppm ST_1 = "%st(1)"
pp ppm ST_2 = "%st(2)"
pp ppm ST_3 = "%st(3)"
pp ppm ST_4 = "%st(4)"
pp ppm ST_5 = "%st(5)"
pp ppm ST_6 = "%st(6)"
pp ppm ST_7 = "%st(7)"
pp ppm EAX = map toLower (show EAX)
pp ppm EBX = map toLower (show EBX)
...etc...
and all those map/toLower calls can now be floated to top level.
This gives a 4% decrease in allocation. But it depends on inlining
a pretty big 'show' function.
With this new patch we get slightly better eta-expansion, which makes
a function look slightly bigger, which just stops it being inlined.
The previous behaviour was luck, so I'm not going to worry about
losing it.
I've added some notes to nofib/Simon-nofib-notes
Diffstat (limited to 'compiler/coreSyn')
| -rw-r--r-- | compiler/coreSyn/CoreArity.lhs | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/compiler/coreSyn/CoreArity.lhs b/compiler/coreSyn/CoreArity.lhs index 12d4274223..ca7216fe29 100644 --- a/compiler/coreSyn/CoreArity.lhs +++ b/compiler/coreSyn/CoreArity.lhs @@ -73,7 +73,8 @@ should have arity 3, regardless of f's arity. \begin{code} manifestArity :: CoreExpr -> Arity --- ^ manifestArity sees how many leading value lambdas there are +-- ^ manifestArity sees how many leading value lambdas there are, +-- after looking through casts manifestArity (Lam v e) | isId v = 1 + manifestArity e | otherwise = manifestArity e manifestArity (Tick t e) | not (tickishIsCode t) = manifestArity e |