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<h3 style="margin-top: 20px; margin-bottom: 10px;">
Simon Peyton Jones pushed to branch wip/T23070-unify 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/0a5139522394b901276ffa71283f01420e270746">0a513952</a></strong>
<div>
<span> by Ben Gamari </span> <i> at 2023-05-11T04:10:17-04:00 </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;'>base: Export GHC.Conc.Sync.fromThreadId

Closes #22706.
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/29be39ba3f187279b19cf451f2d8f58822edab4f">29be39ba</a></strong>
<div>
<span> by Matthew Pickering </span> <i> at 2023-05-11T04:10:54-04:00 </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;'>Build vanilla alpine bindists

We currently attempt to build and distribute fully static alpine
bindists (ones which could be used on any linux platform) but most
people who use the alpine bindists want to use alpine to build their own
static applications (for which a fully static bindist is not necessary).
We should build and distribute these bindists for these users whilst the
fully-static bindist is still unusable.

Fixes #23349
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/40c7daed0c971e58e86a8189f82f72e9213af8b6">40c7daed</a></strong>
<div>
<span> by Simon Peyton Jones </span> <i> at 2023-05-11T04:11:30-04:00 </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;'>Look both ways when looking for quantified equalities

When looking up (t1 ~# t2) in the quantified constraints,
check both orientations.  Forgetting this led to #23333.
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/c17bb82f1cc66cb819acbfc7727a6b366097a323">c17bb82f</a></strong>
<div>
<span> by Rodrigo Mesquita </span> <i> at 2023-05-11T04:12:07-04:00 </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;'>Move "target has RTS linker" out of settings

We move the "target has RTS linker" information out of configure into a
predicate in GHC, and remove this option from the settings file where it
is unnecessary -- it's information statically known from the platform.

Note that previously we would consider `powerpc`s and `s390x`s other
than `powerpc-ibm-aix*` and `s390x-ibm-linux` to have an RTS linker,
but the RTS linker supports neither platform.

Closes #23361
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/bd0b056ea56643bcca1a23b78f72576f9459ce1b">bd0b056e</a></strong>
<div>
<span> by Krzysztof Gogolewski </span> <i> at 2023-05-11T04:12:44-04:00 </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;'>Add a test for #17284

Since !10123 we now reject this program.
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/630b1fea1e41a1e00860a30742b6ab8ade8a0de0">630b1fea</a></strong>
<div>
<span> by Bodigrim </span> <i> at 2023-05-11T04:13:24-04:00 </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;'>Document unlawfulness of instance Num Fixed

Fixes #22712
</pre>
</li>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/80d404f69a9753b28dab79e3897ce5fc5dbd2862">80d404f6</a></strong>
<div>
<span> by Simon Peyton Jones </span> <i> at 2023-05-11T09:21:36+01:00 </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;'>Use the eager unifier in the constraint solver

This patch continues the refactoring of the constraint solver
described in #23070.

The Big Deal in this patch is to call the regular, eager unifier from the
constraint solver, when we want to create new equalities. This
replaces the existing, unifyWanted which amounted to
yet-another-unifier, so it reduces duplication of a rather subtle
piece of technology. See

  * Note [The eager unifier] in GHC.Tc.Utils.Unify
  * GHC.Tc.Solver.Monad.wrapUnifierTcS

I did lots of other refactoring along the way

* I simplified the treatment of right hand sides that contain CoercionHoles.
  Now, a constraint that contains a hetero-kind CoercionHole is non-canonical,
  and cannot be used for rewriting or unification alike.  This required me
  to add the ch_hertero_kind flag to CoercionHole, with consequent knock-on
  effects. See wrinkle (2) of `Note [Equalities with incompatible kinds]` in
  GHC.Tc.Solver.Equality.

* I refactored the StopOrContinue type to add StartAgain, so that after a
  fundep improvement (for example) we can simply start the pipeline again.

* I got rid of the unpleasant (and inefficient) rewriterSetFromType/Co functions.
  With Richard I concluded that they are never needed.

* I discovered Wrinkle (W1) in Note [Wanteds rewrite Wanteds] in
  GHC.Tc.Types.Constraint, and therefore now prioritise non-rewritten equalities.

Quite a few error messages change, I think always for the better.

Compiler runtime stays about the same, with one outlier: a 17% improvement in T17836

Metric Decrease:
    T17836
    T18223
</pre>
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