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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>
</h3>
<h4 style="margin-top: 10px; margin-bottom: 10px;">
Commits:
</h4>
<ul>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/c8000b90e9c2250e65309036743475e90ad7ae9d">c8000b90</a></strong>
<div>
<span> by Sebastian Graf </span> <i> at 2023-04-13T10:09:31+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;'>exprIsTrivial: Factor out shared implementation
The duplication between `exprIsTrivial` and `getIdFromTrivialExpr_maybe` has
been bugging me for a long time.
This patch introduces an inlinable worker function `trivial_expr_fold` acting
as the single, shared decision procedure of triviality. It "returns" a
Church-encoded `Maybe (Maybe Id)`, so when it is inlined, it fuses to similar
code as before.
(Better code, even, in the case of `getIdFromTrivialExpr` which presently
allocates a `Just` constructor that cancels away after this patch.)
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/58ca811db726c5109430b8b23d1431f8076e285d">58ca811d</a></strong>
<div>
<span> by Sebastian Graf </span> <i> at 2023-04-13T11:12:49+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;'>Simplify: Simplification of arguments in a single function
The Simplifier had a function `simplArg` that wasn't called in `rebuildCall`,
which seems to be the main way to simplify args. Hence I consolidated the code
path to call `simplArg`, too, renaming to `simplLazyArg`.
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/eed7c4d1b3817b7db7519617ba18d1d3bcbfe983">eed7c4d1</a></strong>
<div>
<span> by Sebastian Graf </span> <i> at 2023-04-13T11:12:49+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;'>Core.Ppr: Omit case binder for empty case alternatives
A minor improvement to pretty-printing
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/27f108aca4f3d73c07f16ff8407cb78b91e388ab">27f108ac</a></strong>
<div>
<span> by Sebastian Graf </span> <i> at 2023-04-13T11:12:49+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: 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/62f77bf143492f6d983b9533978c21ef920278bd">62f77bf1</a></strong>
<div>
<span> by Sebastian Graf </span> <i> at 2023-04-13T11:12:49+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.
We only do this optimisation with -O2 because we saw 2-3% ghc/alloc regressions
in T4801 and T5321FD.
Fixes #23083.
</pre>
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