[Git][ghc/ghc][wip/warning-for-last-and-init] 14 commits: Adjust the strictness of Data.List.iterate'

6 Sep 2025

      Bodigrim pushed to branch wip/warning-for-last-and-init at Glasgow Haskell Compiler / GHC

Commits:
003b715b by meooow25 at 2025-09-02T23:48:51+02:00
Adjust the strictness of Data.List.iterate'

* Don't force the next element in advance when generating a (:).
* Force the first element to WHNF like every other element.

Now every element in the output list is forced to WHNF when the (:)
containing it is forced.

CLC proposal:
https://github.com/haskell/core-libraries-committee/issues/335

- - - - -
b2f6aad0 by Simon Hengel at 2025-09-03T04:36:10-04:00
Refactoring: More consistently use logOutput, logInfo, fatalErrorMsg

- - - - -
60a16db7 by Rodrigo Mesquita at 2025-09-03T10:55:50+01:00
bytecode: Don't PUSH_L 0; SLIDE 1 1

While looking through bytecode I noticed a quite common unfortunate
pattern:

...
PUSH_L 0
SLIDE 1 1

We do this often by generically constructing a tail call from a function
atom that may be somewhere arbitrary on the stack.
However, for the special case that the function can be found directly on
top of the stack, as part of the arguments, it's plain redundant to push
then slide it.

In this commit we add a small optimisation to the generation of
tailcalls in bytecode. Simply: lookahead for the function in the stack.
If it is the first thing on the stack and it is part of the arguments
which would be dropped as we entered the tail call, then don't push then
slide it.

In a simple example (T26042b), this already produced a drastic
improvement in generated code (left is old, right is with this patch):

```diff
3c3
< 2025-07-29 10:14:02.081277 UTC
---
...
2025-07-29 10:50:36.560949 UTC
160,161c160
<                                            PUSH_L   0
<                                            SLIDE    1 2

...
SLIDE    1 1
164,165d162
<                                       PUSH_L   0
<                                       SLIDE    1 1
175,176c172
<                             PUSH_L   0
<                             SLIDE    1 2
---
...
SLIDE    1 1
179,180d174
<                        PUSH_L   0
<                        SLIDE    1 1
206,207d199
<                        PUSH_L   0
<                        SLIDE    1 1
210,211d201
<                   PUSH_L   0
<                   SLIDE    1 1
214,215d203
<              PUSH_L   0
<              SLIDE    1 1
218,219d205
<         PUSH_L   0
<         SLIDE    1 1
222,223d207
<    PUSH_L   0
<    SLIDE    1 1
...
600,601c566
<                                                 PUSH_L   0
<                                                 SLIDE    1 2
---
...
SLIDE    1 1
604,605d568
<                                            PUSH_L   0
<                                            SLIDE    1 1
632,633d594
<                                            PUSH_L   0
<                                            SLIDE    1 1
636,637d596
<                                       PUSH_L   0
<                                       SLIDE    1 1
640,641d598
<                                  PUSH_L   0
<                                  SLIDE    1 1
644,645d600
<                             PUSH_L   0
<                             SLIDE    1 1
648,649d602
<                        PUSH_L   0
<                        SLIDE    1 1
652,653d604
<                   PUSH_L   0
<                   SLIDE    1 1
656,657d606
<              PUSH_L   0
<              SLIDE    1 1
660,661d608
<         PUSH_L   0
<         SLIDE    1 1
664,665d610
<    PUSH_L   0
<    SLIDE    1 1
```

I also compiled lib:Cabal to bytecode and counted the number of bytecode
lines with `find dist-newstyle -name "*.dump-BCOs" -exec wc {} +`:

    with unoptimized core:
    1190689 lines (before) - 1172891 lines (now)
    = 17798 less redundant instructions (-1.5% lines)

    with optimized core:
    1924818 lines (before) - 1864836 lines (now)
    = 59982 less redundant instructions (-3.1% lines)

- - - - -
8b2c72c0 by L0neGamer at 2025-09-04T06:32:03-04:00
Add Control.Monad.thenM and Control.Applicative.thenA

- - - - -
39e1b7cb by Teo Camarasu at 2025-09-04T06:32:46-04:00
ghc-internal: invert dependency of GHC.Internal.TH.Syntax on Data.Data

This means that Data.Data no longer blocks building TH.Syntax, which
allows greater parallelism in our builds.

We move the Data.Data.Data instances to Data.Data. Quasi depends on
Data.Data for one of its methods, so,
we split the Quasi/Q, etc definition out of GHC.Internal.TH.Syntax
into its own module. This has the added benefit of splitting up this
quite large module.

Previously TH.Syntax was a bottleneck when compiling ghc-internal. Now
it is less of a bottle-neck and is also slightly quicker to
compile (since it no longer contains these instances) at the cost of
making Data.Data slightly more expensive to compile.
TH.Lift which depends on TH.Syntax can also compile quicker and no
longer blocks ghc-internal finishing to compile.

Resolves #26217

-------------------------
Metric Decrease:
    MultiLayerModulesTH_OneShot
    T13253
    T21839c
    T24471
Metric Increase:
    T12227
-------------------------

- - - - -
bdf82fd2 by Teo Camarasu at 2025-09-04T06:32:46-04:00
compiler: delete unused names in Builtins.Names.TH

returnQ and bindQ are no longer used in the compiler.
There was also a very old comment that referred to them that I have modernized

- - - - -
41a448e5 by Ben Gamari at 2025-09-04T19:21:43-04:00
hadrian: Pass lib & include directories to ghc `Setup configure`

- - - - -
46bb9a79 by Ben Gamari at 2025-09-04T19:21:44-04:00
rts/IPE: Fix compilation when zstd is enabled

This was broken by the refactoring undertaken in
c80dd91c0bf6ac034f0c592f16c548b9408a8481.

Closes #26312.

- - - - -
138a6e34 by sheaf at 2025-09-04T19:22:46-04:00
Make mkCast assertion a bit clearer

This commit changes the assertion message that gets printed when one
calls mkCast with a coercion whose kind does not match the type of the
inner expression. I always found the assertion message a bit confusing,
as it didn't clearly state what exactly was the error.

- - - - -
9d626be1 by sheaf at 2025-09-04T19:22:46-04:00
Simplifier/rules: fix mistakes in Notes & comments

- - - - -
3504255c by Mike Pilgrem at 2025-09-06T11:06:38+01:00
Re CLC issue 292 Warn GHC.Internal.List.{init,last} are partial

Also corrects the warning for `tail` to refer to `Data.List.uncons` (like the existing warning for `head`).

In module `Settings.Warnings`, applies `-Wno-unrecognised-warning-flags` `-Wno-x-partial` to the `Cabal`, `filepath`, `hsc2hs`, `hpc`, `parsec`, `text` and `time` packages (outside GHC's repository).

Also bumps submodules.

- - - - -
0766a9a3 by Andrew Lelechenko at 2025-09-06T11:06:43+01:00
Wibble

- - - - -
36121840 by Andrew Lelechenko at 2025-09-06T11:06:43+01:00
Wobble

- - - - -
6f3e2ac3 by Andrew Lelechenko at 2025-09-06T11:07:55+01:00
Revert filepath

- - - - -

79 changed files:

- compiler/GHC/Builtin/Names/TH.hs
- compiler/GHC/Core/Lint.hs
- compiler/GHC/Core/Opt/Simplify.hs
- compiler/GHC/Core/Opt/SpecConstr.hs
- compiler/GHC/Core/Rules.hs
- compiler/GHC/Core/Utils.hs
- compiler/GHC/Data/IOEnv.hs
- compiler/GHC/Driver/CodeOutput.hs
- compiler/GHC/Driver/Pipeline/Execute.hs
- compiler/GHC/Driver/Session/Units.hs
- compiler/GHC/Hs/Expr.hs
- compiler/GHC/HsToCore/Quote.hs
- compiler/GHC/Iface/Load.hs
- compiler/GHC/Linker/Loader.hs
- compiler/GHC/Prelude/Basic.hs
- compiler/GHC/Rename/Splice.hs
- compiler/GHC/Stg/Lint.hs
- compiler/GHC/StgToByteCode.hs
- compiler/GHC/Tc/Gen/Splice.hs
- compiler/GHC/Tc/Gen/Splice.hs-boot
- compiler/GHC/Tc/Types/TH.hs
- compiler/GHC/Tc/Utils/Monad.hs
- ghc/GHCi/UI.hs
- ghc/Main.hs
- hadrian/src/Settings/Packages.hs
- hadrian/src/Settings/Warnings.hs
- libraries/base/changelog.md
- libraries/base/src/Control/Applicative.hs
- libraries/base/src/Control/Monad.hs
- libraries/base/src/Data/Array/Byte.hs
- libraries/base/src/Data/Fixed.hs
- + libraries/ghc-boot-th/GHC/Boot/TH/Monad.hs
- libraries/ghc-boot-th/GHC/Boot/TH/Ppr.hs
- libraries/ghc-boot-th/ghc-boot-th.cabal.in
- libraries/ghc-internal/ghc-internal.cabal.in
- libraries/ghc-internal/src/GHC/Internal/Base.hs
- libraries/ghc-internal/src/GHC/Internal/Control/Monad.hs
- libraries/ghc-internal/src/GHC/Internal/Data/Data.hs
- libraries/ghc-internal/src/GHC/Internal/Float.hs
- libraries/ghc-internal/src/GHC/Internal/List.hs
- libraries/ghc-internal/src/GHC/Internal/System/IO.hs
- libraries/ghc-internal/src/GHC/Internal/TH/Lib.hs
- libraries/ghc-internal/src/GHC/Internal/TH/Lift.hs
- + libraries/ghc-internal/src/GHC/Internal/TH/Monad.hs
- libraries/ghc-internal/src/GHC/Internal/TH/Quote.hs
- libraries/ghc-internal/src/GHC/Internal/TH/Syntax.hs
- libraries/ghci/GHCi/Message.hs
- libraries/ghci/GHCi/TH.hs
- libraries/template-haskell/Language/Haskell/TH/Quote.hs
- libraries/template-haskell/Language/Haskell/TH/Syntax.hs
- libraries/template-haskell/vendored-filepath/System/FilePath/Posix.hs
- libraries/template-haskell/vendored-filepath/System/FilePath/Windows.hs
- rts/IPE.c
- testsuite/tests/deriving/should_compile/T14682.stderr
- testsuite/tests/deriving/should_compile/drv-empty-data.stderr
- testsuite/tests/driver/j-space/jspace.hs
- testsuite/tests/interface-stability/base-exports.stdout
- testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs
- testsuite/tests/interface-stability/base-exports.stdout-mingw32
- testsuite/tests/interface-stability/base-exports.stdout-ws-32
- testsuite/tests/interface-stability/template-haskell-exports.stdout
- testsuite/tests/plugins/plugins10.stdout
- testsuite/tests/profiling/should_run/callstack001.stdout
- testsuite/tests/rts/KeepCafsBase.hs
- testsuite/tests/splice-imports/SI29.stderr
- testsuite/tests/th/T11452.stderr
- testsuite/tests/th/T15321.stderr
- testsuite/tests/th/T7276.stderr
- testsuite/tests/th/TH_NestedSplicesFail3.stderr
- testsuite/tests/th/TH_NestedSplicesFail4.stderr
- utils/check-exact/Main.hs
- utils/check-exact/Transform.hs
- utils/check-exact/Utils.hs
- utils/ghc-pkg/Main.hs
- utils/ghc-toolchain/src/GHC/Toolchain/CheckArm.hs
- utils/haddock/haddock-api/src/Haddock/Backends/Xhtml.hs
- utils/haddock/haddock-library/src/Documentation/Haddock/Parser.hs
- utils/hpc
- utils/hsc2hs

The diff was not included because it is too large.

View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/8e33c7de40d0cf676077c22c498a343...

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/8e33c7de40d0cf676077c22c498a343...
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Bodigrim (＠Bodigrim)

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