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| author | Sebastian Graf <sebastian.graf@kit.edu> | 2022-02-17 18:11:24 +0100 |
|---|---|---|
| committer | Sebastian Graf <sebastian.graf@kit.edu> | 2022-05-03 20:11:51 +0200 |
| commit | 15ffe2b02e927d9cc2cc0f97dddee38decea5f56 (patch) | |
| tree | 904bd87b75e510d58b3dfdf437f5b469b6f6ccc9 /compiler/GHC/Stg | |
| parent | 4a7809284354025d07221f0aeca10a7992d23677 (diff) | |
| download | haskell-15ffe2b02e927d9cc2cc0f97dddee38decea5f56.tar.gz | |
Assume at least one evaluation for nested SubDemands (#21081, #21133)wip/T21081
See the new `Note [SubDemand denotes at least one evaluation]`.
A demand `n :* sd` on a let binder `x=e` now means
> "`x` was evaluated `n` times and in any program trace it is evaluated, `e` is
> evaluated deeply in sub-demand `sd`."
The "any time it is evaluated" premise is what this patch adds. As a result,
we get better nested strictness. For example (T21081)
```hs
f :: (Bool, Bool) -> (Bool, Bool)
f pr = (case pr of (a,b) -> a /= b, True)
-- before: <MP(L,L)>
-- after: <MP(SL,SL)>
g :: Int -> (Bool, Bool)
g x = let y = let z = odd x in (z,z) in f y
```
The change in demand signature "before" to "after" allows us to case-bind `z`
here.
Similarly good things happen for the `sd` in call sub-demands `Cn(sd)`, which
allows for more eta-reduction (which is only sound with `-fno-pedantic-bottoms`,
albeit).
We also fix #21085, a surprising inconsistency with `Poly` to `Call` sub-demand
expansion.
In an attempt to fix a regression caused by less inlining due to eta-reduction
in T15426, I eta-expanded the definition of `elemIndex` and `elemIndices`, thus
fixing #21345 on the go.
The main point of this patch is that it fixes #21081 and #21133.
Annoyingly, I discovered that more precise demand signatures for join points can
transform a program into a lazier program if that join point gets floated to the
top-level, see #21392. There is no simple fix at the moment, but !5349 might.
Thus, we accept a ~5% regression in `MultiLayerModulesTH_OneShot`, where #21392
bites us in `addListToUniqDSet`. T21392 reliably reproduces the issue.
Surprisingly, ghc/alloc perf on Windows improves much more than on other jobs, by
0.4% in the geometric mean and by 2% in T16875.
Metric Increase:
MultiLayerModulesTH_OneShot
Metric Decrease:
T16875
Diffstat (limited to 'compiler/GHC/Stg')
| -rw-r--r-- | compiler/GHC/Stg/InferTags/Rewrite.hs | 3 | ||||
| -rw-r--r-- | compiler/GHC/Stg/Lift/Analysis.hs | 2 |
2 files changed, 2 insertions, 3 deletions
diff --git a/compiler/GHC/Stg/InferTags/Rewrite.hs b/compiler/GHC/Stg/InferTags/Rewrite.hs index e35f700377..8076507a1c 100644 --- a/compiler/GHC/Stg/InferTags/Rewrite.hs +++ b/compiler/GHC/Stg/InferTags/Rewrite.hs @@ -38,7 +38,6 @@ import GHC.Stg.Syntax as StgSyn import GHC.Data.Maybe import GHC.Utils.Panic -import GHC.Utils.Panic.Plain import GHC.Utils.Outputable import GHC.Utils.Monad.State.Strict @@ -425,7 +424,7 @@ rewriteApp _ (StgApp f args) | Just marks <- idCbvMarks_maybe f , relevant_marks <- dropWhileEndLE (not . isMarkedCbv) marks , any isMarkedCbv relevant_marks - = assert (length relevant_marks <= length args) + = assertPpr (length relevant_marks <= length args) (ppr f $$ ppr args $$ ppr relevant_marks) unliftArg relevant_marks where diff --git a/compiler/GHC/Stg/Lift/Analysis.hs b/compiler/GHC/Stg/Lift/Analysis.hs index 6fc116c8bc..6b46b5125c 100644 --- a/compiler/GHC/Stg/Lift/Analysis.hs +++ b/compiler/GHC/Stg/Lift/Analysis.hs @@ -326,7 +326,7 @@ tagSkeletonRhs bndr (StgRhsClosure fvs ccs upd bndrs body) rhsCard :: Id -> Card rhsCard bndr | is_thunk = oneifyCard n - | otherwise = peelManyCalls (idArity bndr) cd + | otherwise = n `multCard` peelManyCalls (idArity bndr) cd where is_thunk = idArity bndr == 0 -- Let's pray idDemandInfo is still OK after unarise... |