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  • !2165

Closed
Opened Nov 13, 2019 by Andrew Martin@andrewthadDeveloper
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Check out, review, and merge locally

Step 1. Fetch and check out the branch for this merge request

git fetch "https://gitlab.haskell.org/andrewthad/ghc.git" "cstring_length"
git checkout -b "andrewthad/ghc-cstring_length" FETCH_HEAD

Step 2. Review the changes locally

Step 3. Merge the branch and fix any conflicts that come up

git fetch origin
git checkout "master"
git merge --no-ff "andrewthad/ghc-cstring_length"

Step 4. Push the result of the merge to GitLab

git push origin "master"

Note that pushing to GitLab requires write access to this repository.

Tip: You can also checkout merge requests locally by following these guidelines.

Implement known-key cstringLength# and its rule

  • Overview 111
  • Commits 1
  • Pipelines 32
  • Changes 19

This function and its accompanying rule resolve issue #5218 (closed). A future PR to the bytestring library will make the internal Data.ByteString.Internal.unsafePackAddress compute string length with cstringLength#. This will improve the status quo because it is eligible for constant folding.

Additionally, introduce a new data constructor to ForeignPtrContents named FinalPtr. This additional data constructor, when used in the IsString instance for ByteString, leads to more Core-to-Core optimization opportunities, fewer runtime allocations, and smaller binaries.

Also, this commit re-exports all the functions from GHC.CString (including cstringLength#) in GHC.Exts. It also adds a new test driver. This test driver is used to perform substring matches on Core that is dumped after all the simplifier passes. In this commit, it is used to check that constant folding of cstringLength# works.

Edited Apr 30, 2020 by Ben Gamari
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Reference: ghc/ghc!2165
Source branch: cstring_length