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| author | Sebastian Graf <sebastian.graf@kit.edu> | 2020-10-30 17:20:37 +0100 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-11-20 02:09:51 -0500 |
| commit | 0aec78b6c97cee58ba20bfcb959f1369b80c4e4c (patch) | |
| tree | 3e48861640dbeb7a9d7784f0f02c2bc564af50ec /compiler/GHC/Utils | |
| parent | 321d1bd8a79ab39c3c9e8697fffb0107c43f83cf (diff) | |
| download | haskell-0aec78b6c97cee58ba20bfcb959f1369b80c4e4c.tar.gz | |
Demand: Interleave usage and strictness demands (#18903)
As outlined in #18903, interleaving usage and strictness demands not
only means a more compact demand representation, but also allows us to
express demands that we weren't easily able to express before.
Call demands are *relative* in the sense that a call demand `Cn(cd)`
on `g` says "`g` is called `n` times. *Whenever `g` is called*, the
result is used according to `cd`". Example from #18903:
```hs
h :: Int -> Int
h m =
let g :: Int -> (Int,Int)
g 1 = (m, 0)
g n = (2 * n, 2 `div` n)
{-# NOINLINE g #-}
in case m of
1 -> 0
2 -> snd (g m)
_ -> uncurry (+) (g m)
```
Without the interleaved representation, we would just get `L` for the
strictness demand on `g`. Now we are able to express that whenever
`g` is called, its second component is used strictly in denoting `g`
by `1C1(P(1P(U),SP(U)))`. This would allow Nested CPR to unbox the
division, for example.
Fixes #18903.
While fixing regressions, I also discovered and fixed #18957.
Metric Decrease:
T13253-spj
Diffstat (limited to 'compiler/GHC/Utils')
| -rw-r--r-- | compiler/GHC/Utils/Outputable.hs | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/compiler/GHC/Utils/Outputable.hs b/compiler/GHC/Utils/Outputable.hs index 16e66ce6d1..3698c5a4b2 100644 --- a/compiler/GHC/Utils/Outputable.hs +++ b/compiler/GHC/Utils/Outputable.hs @@ -35,6 +35,7 @@ module GHC.Utils.Outputable ( doubleQuotes, angleBrackets, semi, comma, colon, dcolon, space, equals, dot, vbar, arrow, lollipop, larrow, darrow, arrowt, larrowt, arrowtt, larrowtt, + lambda, lparen, rparen, lbrack, rbrack, lbrace, rbrace, underscore, mulArrow, blankLine, forAllLit, bullet, (<>), (<+>), hcat, hsep, @@ -648,7 +649,7 @@ quotes d = sdocOption sdocCanUseUnicode $ \case | otherwise -> Pretty.quotes pp_d semi, comma, colon, equals, space, dcolon, underscore, dot, vbar :: SDoc -arrow, lollipop, larrow, darrow, arrowt, larrowt, arrowtt, larrowtt :: SDoc +arrow, lollipop, larrow, darrow, arrowt, larrowt, arrowtt, larrowtt, lambda :: SDoc lparen, rparen, lbrack, rbrack, lbrace, rbrace, blankLine :: SDoc blankLine = docToSDoc $ Pretty.text "" @@ -661,6 +662,7 @@ arrowt = unicodeSyntax (char '⤚') (docToSDoc $ Pretty.text ">-") larrowt = unicodeSyntax (char '⤙') (docToSDoc $ Pretty.text "-<") arrowtt = unicodeSyntax (char '⤜') (docToSDoc $ Pretty.text ">>-") larrowtt = unicodeSyntax (char '⤛') (docToSDoc $ Pretty.text "-<<") +lambda = unicodeSyntax (char 'λ') (char '\\') semi = docToSDoc $ Pretty.semi comma = docToSDoc $ Pretty.comma colon = docToSDoc $ Pretty.colon |