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Last edited by Andreas Klebinger
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AndreasPK

This is a scrap page, so things might be duplicated and those kinds of things.

Tickets I'm interested in:

#9660 - After/During tag inference

Current agenda:

IO Manager: !1224 (diffs)
This is currently my main focus. Things below are on my list but not neccesarily listed by priority.

#16354 - LLVM broken on windows - TODO

Also include it in CI: AndreasK, Ideally we would handle LLVM toolchain the same way we handle GHC and xcabal-install 3:59 PM see .gitlab/win32-init.sh

Pointer tagging in GHC (various tickets, see below).

  • #16970 - Tag inference work
  • #18285 - GHC should keep unfoldings for recursive functions which are suitable for specialization.
  • #17238 - Generate lookup tables instead of jump tables where possible.
  • !1990 - Use dataToTag - needs work
  • #17092 - Implement stack check elision - TODO
  • #7741 - NCG-SIMD - TODO

Things to do in the near future:

  • SIMD

  • Branch likelyhood: #14672

  • Register allocator improvements: #7063, #8048, #12232, #13051, #16243

  • Avoid certain stack checks: #17092

  • #17784 lookupIdSubst fails because bindings are not in dep order.

  • #13535 Simplifier choking on vector test suite

  • !2580 (closed) - Update RULES for elem

  • !2575 (closed) - MR to enable fdicts-strict by default. Seems to be correct, needs perf analysis.

  • !2574 (closed)- Refactor DataCon codegen - needs review

  • #17759 investigate base functions which currently fail to specialize

  • #9342 - Branchless Int operations

  • #17237 Cmm FloatOut - Put shared cmm statements into the common path

  • #17238 Generate lookup instead of jump tables

  • #17242 Use dataToTag# for Eq instances

  • #17240 Code duplication for code evaluating arguments.

  • #1257 (closed) - Support unboxed tuples in GHCi/bytecode.

  • #13763 - Runtime (register alloc?) regression

Maybe eventually list

Most things runtime performance related

Out of the above these have likely bounded time requirements

  • #17242 Use dataToTag# for Eq instances
  • #9342 - Branchless Int operations
  • #17238 Generate lookup instead of jump tables

Regressions worth looking into

#17133

Pointer tagging in GHC

See also the "pointer tagging" tag: issues

#14373 (closed) Pointer tagging for large families

Instead of tagging large families with a flag indicating evaluation, tag them with the tag if possible and the flag only for constructors not fitting in the tag.

This is a project of Gabor Greif and he indicated he still want's to finish this recently (@ICFP 2019)

He stated this is blocked on #15155 in the past but I did not look into why/how.

#17004 (closed) Export LFInfo for bindings

This patch exposes the backends view of exported ids in interface files.

The benefits are that we can:

  • Tag certain bindings which do not have an unfolding otherwise.
  • Get accurate information about arity after all transformations have been applied

The benefits of this are:

  • We can omit code to enter closures if we know statically they are evaluated constructors.
  • We avoid entering closures since more closures will be appropriately tagged
  • We can omit entry code for all constructors. If we can ensure all references to constructors are tagged there is never a reason to enter them.
  • We can use a more efficient calling convention in some places, as LFInfo allows us to replace slow calls with more efficient variants.

Untagged pointers find their way into strict fields.

There are two tickets about this currently:

  • #15155 How untagged pointers sneak into banged fields
  • #14677 Code generator does not correctly tag a pointer

Both are related to #16970, implementing #16970 will also fix both of these.

Other smaller issues:

See the issues tagged with pointer tagging on the tracker.

GHC API

Using the API to compile a String to Core

https://gist.github.com/AndreasPK/0c7ec8a6f01974c92271e54133a7aad0