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<h3>
Ben Gamari pushed to branch wip/T15808
at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
</h3>
<h4>
Commits:
</h4>
<ul>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/57c3db9612463426e1724816fd3f98142fec0e31">57c3db96</a></strong>
<div>
<span>by Ryan Scott</span>
<i>at 2020-10-31T02:53:55-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Make typechecker equality consider visibility in ForAllTys

Previously, `can_eq_nc'` would equate `ForAllTy`s regardless of their
`ArgFlag`, including `forall i -> i -> Type` and `forall i. i -> Type`! To fix
this, `can_eq_nc'` now uses the `sameVis` function to first check if the
`ArgFlag`s are equal modulo specificity. I have also updated `tcEqType`'s
implementation to match this behavior. For more explanation on the "modulo
specificity" part, see the new `Note [ForAllTy and typechecker equality]`
in `GHC.Tc.Solver.Canonical`.

While I was in town, I fixed some related documentation issues:

* I added `Note [Typechecker equality]` to `GHC.Tc.Utils.TcType` to describe
  what exactly distinguishes `can_eq_nc'` and `tcEqType` (which implement
  typechecker equality) from `eqType` (which implements definitional equality,
  which does not care about the `ArgFlags` of `ForAllTy`s at all).
* The User's Guide had some outdated prose on the specified/inferred
  distinction being different for types and kinds, a holdover from #15079. This
  is no longer the case on today's GHC, so I removed this prose, added some new
  prose to take its place, and added a regression test for the programs in
  #15079.
* The User's Guide had some _more_ outdated prose on inferred type variables
  not being allowed in `default` type signatures for class methods, which is no
  longer true as of the resolution of #18432.
* The related `Note [Deferred Unification]` was being referenced as
  `Note [Deferred unification]` elsewhere, which made it harder to `grep`
  for. I decided to change the name of the Note to `Deferred unification`
  for consistency with the capitalization style used for most other Notes.

Fixes #18863.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/a98593f0c7623843a787af5fb628336cb897c527">a98593f0</a></strong>
<div>
<span>by Sylvain Henry</span>
<i>at 2020-10-31T02:54:34-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Refactor numeric constant folding rules

Avoid the use of global pattern synonyms.

1) I think it's going to be helpful to implement constant folding for
   other numeric types, especially Natural which doesn't have a wrapping
   behavior. We'll have to refactor these rules even more so we'd better
   make them less cryptic.

2) It should also be slightly faster because global pattern synonyms
   matched operations for every numeric types instead of the current one:
   e.g., ":**:" pattern was matching multiplication for both Int# and
   Word# types. As we will probably want to implement constant folding
   for other numeric types (Int8#, Int16#, etc.), it is more efficient
   to only match primops for a given type as we do now.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/730ef38f467d67f4f664b2b4a5f4b236864e97b2">730ef38f</a></strong>
<div>
<span>by Sylvain Henry</span>
<i>at 2020-10-31T02:54:34-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Simplify constant-folding (#18032)

See #18032 for the details.

* Use `Lit (LitNumber _ i)` instead of `isLitValue_maybe` which does
  more work but that is not needed for constant-folding
* Don't export `GHC.Types.Literal.isLitValue_maybe`
* Kill `GHC.Types.Literal.isLitValue` which isn't used
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/d5a53c1aa6a417a466deb5951c0cc4cd94be97c0">d5a53c1a</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-10-31T02:55:10-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">primops.txt.pp: Move ByteArray# primops to separate file

This file will be generated.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/b4278a41a18132a981b25c59b296cdf3ba970024">b4278a41</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-10-31T02:55:10-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">primops: Generate ByteArray# index/read/write primops

Previously these were mostly undocumented and was ripe for potential
inconsistencies.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/08e6993a1b956e6edccdc1cecc7250b724bf79a0">08e6993a</a></strong>
<div>
<span>by Sylvain Henry</span>
<i>at 2020-10-31T02:55:50-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Move loadDecl into IfaceToCore
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/cb1f755c6fb77f140aee11fdc7b4da04dd5dcd02">cb1f755c</a></strong>
<div>
<span>by Tamar Christina</span>
<i>at 2020-10-31T09:26:56-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">winio: Fix unused variables warnings
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/eb368078204bceba51e3c80e387ce1d776762cfd">eb368078</a></strong>
<div>
<span>by Andrzej Rybczak</span>
<i>at 2020-10-31T09:27:34-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Add testcase for #816
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/6d21ecee535782f01dba9947a49e282afee25724">6d21ecee</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-10-31T13:34:45-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">rts/linker: Fix relocation overflow in PE linker

Previously the overflow check for the IMAGE_REL_AMD64_ADDR32NB
relocation failed to account for the signed nature of the value.
Specifically, the overflow check was:

    uint64_t v;
    v = S + A;
    if (v >> 32) { ... }

However, `v` ultimately needs to fit into 32-bits as a signed value.
Consequently, values `v > 2^31` in fact overflow yet this is not caught
by the existing overflow check.

Here we rewrite the overflow check to rather ensure that
`INT32_MIN <= v <= INT32_MAX`. There is now quite a bit of repetition
between the `IMAGE_REL_AMD64_REL32` and `IMAGE_REL_AMD64_ADDR32` cases
but I am leaving fixing this for future work.

This bug was first noticed by @awson.

Fixes #15808.
</pre>
</li>
</ul>
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