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<h3>
Marge Bot pushed to branch master
at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
</h3>
<h4>
Commits:
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<ul>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/321d1bd8a79ab39c3c9e8697fffb0107c43f83cf">321d1bd8</a></strong>
<div>
<span>by Sebastian Graf</span>
<i>at 2020-11-20T02:09:51-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Fix strictness signatures of `prefetchValue*#` primops
Their strictness signatures said the primops are strict in their first
argument, which is wrong: Handing it a thunk will prefetch the pointer
to the thunk, but not evaluate it. Hence not strict.
The regression test `T8256` actually tests for laziness in the first
argument, so GHC apparently never exploited the strictness signature.
See also https://gitlab.haskell.org/ghc/ghc/-/issues/8256#note_310867,
where this came up.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/0aec78b6c97cee58ba20bfcb959f1369b80c4e4c">0aec78b6</a></strong>
<div>
<span>by Sebastian Graf</span>
<i>at 2020-11-20T02:09:51-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">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
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/3a55b3a2574f913d046f3a6f82db48d7f6df32e3">3a55b3a2</a></strong>
<div>
<span>by Sebastian Graf</span>
<i>at 2020-11-20T02:09:51-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Update user's guide entry on demand analysis and worker/wrapper
The demand signature notation has been undocumented for a long time.
The only source to understand it, apart from reading the `Outputable`
instance, has been an outdated wiki page.
Since the previous commits have reworked the demand lattice, I took
it as an opportunity to also write some documentation about notation.
</pre>
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<a href="#451725cc4e5d443a3b7c2adcdf224840f953b7e2">
compiler/GHC/Builtin/primops.txt.pp
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<a href="#c1bf6b849619bc8d7ef37a97d993dbfaa9966f7b">
compiler/GHC/Core/Opt/CprAnal.hs
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<a href="#8104fa1b71db6cfc4eb90cd769463d9eb9004619">
compiler/GHC/Core/Opt/DmdAnal.hs
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<a href="#bd153f89bc48f3fd5079b51fb799808aacbd750c">
compiler/GHC/Core/Opt/Pipeline.hs
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compiler/GHC/Core/Opt/SetLevels.hs
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compiler/GHC/Core/Opt/Simplify.hs
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compiler/GHC/Core/Opt/Simplify/Utils.hs
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compiler/GHC/Core/Opt/SpecConstr.hs
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compiler/GHC/Core/Opt/WorkWrap/Utils.hs
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compiler/GHC/CoreToStg.hs
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compiler/GHC/CoreToStg/Prep.hs
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compiler/GHC/Iface/Syntax.hs
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compiler/GHC/Stg/Lift/Analysis.hs
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compiler/GHC/Types/Demand.hs
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compiler/GHC/Types/Id.hs
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compiler/GHC/Types/Id/Info.hs
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compiler/GHC/Types/Id/Make.hs
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compiler/GHC/Utils/Outputable.hs
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docs/users_guide/9.2.1-notes.rst
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docs/users_guide/debugging.rst
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docs/users_guide/exts/instances.rst
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testsuite/tests/arityanal/should_compile/Arity01.stderr
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testsuite/tests/arityanal/should_compile/Arity05.stderr
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testsuite/tests/arityanal/should_compile/Arity11.stderr
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testsuite/tests/arityanal/should_compile/Arity14.stderr
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