#7520: Implement cardinality analysis
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.6.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------
Ilya is well on the way to a cardinality analyser. Today I realised that
it'll help a lot with CPS-heavy code. For example, here's what happens
with
{{{
data DT = DT {
field1 :: Int
, field2 :: Int
, field3 :: Int }
deriving( Read )
}}}
After strictness analysis and simplification we get this:
{{{
$wa_sD5 =
\ (ww_sD1 :: GHC.Prim.Int#)
(@ b_awu)
(w_sD3 :: W2.DT -> Text.ParserCombinators.ReadP.P b_awu) ->
case GHC.Prim.<=# ww_sD1 11 of _ {
GHC.Types.False -> Text.ParserCombinators.ReadP.Fail @ b_awu;
GHC.Types.True ->
Text.Read.Lex.expect1
a_su6
@ b_awu
(\ _ ->
Text.Read.Lex.expect1
a_suf
@ b_awu
(\ _ ->
Text.Read.Lex.expect1
a_sum
@ b_awu
(\ _ ->
Text.Read.Lex.expect1
a_suv
@ b_awu
(\ _ ->
GHC.Read.$fReadInt5
GHC.Read.$fReadInt_$sconvertInt
Text.ParserCombinators.ReadPrec.minPrec
@ b_awu
(\ (a2_XB0 [Dmd=Just L] :: GHC.Types.Int) ->
Text.Read.Lex.expect1
lvl_svA
@ b_awu
(\ _ ->
Text.Read.Lex.expect1
lvl_svE
@ b_awu
(\ _ ->
Text.Read.Lex.expect1
lvl_svI
@ b_awu
(\ _ ->
GHC.Read.$fReadInt5
GHC.Read.$fReadInt_$sconvertInt
Text.ParserCombinators.ReadPrec.minPrec
@ b_awu
(\ (a2_XBa [Dmd=Just L]
:: GHC.Types.Int) ->
...
}}}
Look at all those nested continuations! Then the subsequent float-out pass
floats out lots of MFEs, but entirely fruitlessly because all these are
actually one-shot lambdas.
I'm not certain that the analysis will catch them all, but it might.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7520>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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