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<h3 style="margin-top: 20px; margin-bottom: 10px;">
Sebastian Graf pushed to branch wip/T23083 at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
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Commits:
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<ul>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/e04ec8f5d5654929fc6693b30a3e6f1d07a1ad14">e04ec8f5</a></strong>
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<span> by Sebastian Graf </span> <i> at 2023-04-03T11:16:25+02:00 </i>
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<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.875rem; color: #333238; position: relative; font-family: var(--default-mono-font, "Menlo"),"DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dcdcde;'>Core.Ppr: Omit case binder for empty case alternatives
A minor improvement to pretty-printing
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</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/18578d3156cadc10aba00a5d0eb6933432463e1e">18578d31</a></strong>
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<span> by Sebastian Graf </span> <i> at 2023-04-03T11:19:33+02:00 </i>
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<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.875rem; color: #333238; position: relative; font-family: var(--default-mono-font, "Menlo"),"DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dcdcde;'>exprIsTrivial: Factor out shared implementation and introduce TrivialExpr
The duplication between `exprIsTrivial` and `getIdFromTrivialExpr_maybe` (along
with its lacking check that the returned Var is indeed an Id) has been bugging
me for a long time.
This patch introduces a inlinable worker function `trivial_expr_fold`
acting as the single, shared decision procedure of triviality.
It "returns" a Church-encoded `Maybe TrivialExpr`, so when it is inlined, it
fuses to similar code as before.
This allows us to export a generalisation of `getIdFromTrivialExpr_maybe` that
returns any `TrivialExpr` I dubbed `trivialExpr[_maybe]`. It will be of use in
!10088 during CoreToStg, where we want to look into scrutinees of empty case
alternatives and thus is ultimately part of #23083.
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/105494e08418cb08a357863e28394c3278d0593c">105494e0</a></strong>
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<span> by Sebastian Graf </span> <i> at 2023-04-03T11:19:54+02:00 </i>
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<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.875rem; color: #333238; position: relative; font-family: var(--default-mono-font, "Menlo"),"DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dcdcde;'>CorePrep: Do not eliminate EmptyCase, do it in StgToCmm instead
We eliminate EmptyCase by way of `cgCase e _ _ [] = cgExpr e` now.
The main reason is that it plays far better in conjunction with eta expansion
(as we aim to do for arguments in CorePrep, #23083), because we can discard
any arguments, `(case e of {}) eta == case e of {}`, whereas in `(e |> co) eta`
it's impossible to discard the argument.
It is also both much simpler to describe than the previous mechanism of emitting
an unsafe coercion and simpler to implement, removing quite a bit of commentary
and the `Bool` field of `CorePrepProv`.
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/26ff3536bf7de746899a5a5de9cfb0295227bfba">26ff3536</a></strong>
<div>
<span> by Sebastian Graf </span> <i> at 2023-04-03T11:21:42+02:00 </i>
</div>
<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.875rem; color: #333238; position: relative; font-family: var(--default-mono-font, "Menlo"),"DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dcdcde;'>CorePrep: Eta expand arguments (#23083)
Previously, we'd only eta expand let bindings and lambdas,
now we'll also eta expand arguments such as in T23083:
```hs
g f h = f (h `seq` (h $))
```
Unless `-fpedantic-bottoms` is set, we'll now transform to
```hs
g f h = f (\eta -> h eta)
```
in CorePrep.
See the new `Note [Eta expansion of arguments in CorePrep]` for the details.
Fixes #23083.
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