[Git][ghc/ghc][wip/T23083] 5 commits: Inlining literals into boring contexts is OK

[Sebastian Graf (@sgraf812)]

Sebastian Graf pushed to branch wip/T23083 at Glasgow Haskell Compiler / GHC


Commits:
a2050f56 by Sebastian Graf at 2023-04-27T16:13:05+02:00
Inlining literals into boring contexts is OK

- - - - -
09940bde by Sebastian Graf at 2023-04-27T16:13:12+02:00
Kill SetLevel.notWorthFloating.is_triv (#23270)

We have had it since b84ba676034, when it operated on annotated expressions.
Nowadays it operates on vanilla `CoreExpr` though, so we should just call
`exprIsTrivial`; thus handling empty cases and string literals correctly.

- - - - -
85d1fb59 by Sebastian Graf at 2023-04-27T16:34:32+02:00
ANFise string literal arguments (#23270)

This instates the invariant that a trivial CoreExpr translates to an atomic
StgExpr. Nice.

Fixes #23270.

- - - - -
b3916756 by Sebastian Graf at 2023-04-27T16:35:50+02:00
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`.

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e6893f0a by Sebastian Graf at 2023-04-27T16:35:50+02:00
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.

- - - - -


30 changed files:

- compiler/GHC/Core.hs
- compiler/GHC/Core/Coercion.hs
- compiler/GHC/Core/Coercion/Opt.hs
- compiler/GHC/Core/FVs.hs
- compiler/GHC/Core/Lint.hs
- compiler/GHC/Core/Opt/SetLevels.hs
- compiler/GHC/Core/TyCo/FVs.hs
- compiler/GHC/Core/TyCo/Rep.hs
- compiler/GHC/Core/TyCo/Subst.hs
- compiler/GHC/Core/TyCo/Tidy.hs
- compiler/GHC/Core/Type.hs
- compiler/GHC/Core/Unfold.hs
- compiler/GHC/CoreToIface.hs
- compiler/GHC/CoreToStg.hs
- compiler/GHC/CoreToStg/Prep.hs
- compiler/GHC/Driver/Config/CoreToStg/Prep.hs
- compiler/GHC/Driver/Flags.hs
- compiler/GHC/Driver/Session.hs
- compiler/GHC/Iface/Syntax.hs
- compiler/GHC/Iface/Type.hs
- compiler/GHC/IfaceToCore.hs
- compiler/GHC/Stg/CSE.hs
- compiler/GHC/Stg/Unarise.hs
- compiler/GHC/StgToCmm/Expr.hs
- compiler/GHC/StgToJS/Expr.hs
- compiler/GHC/Tc/TyCl/Utils.hs
- compiler/GHC/Tc/Utils/TcMType.hs
- compiler/GHC/Utils/Trace.hs
- docs/users_guide/using-optimisation.rst
- + testsuite/tests/core-to-stg/T23270.hs


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/084fb6480828ee322dd35c0d8559ea38d6a70f0d...e6893f0a1eb36d59cbd7a1c13434b8216083f35b

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/084fb6480828ee322dd35c0d8559ea38d6a70f0d...e6893f0a1eb36d59cbd7a1c13434b8216083f35b
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