[AArch64][GlobalISel] ABD operations and combines

[davemgreen]

SDAG, via these nodes can pattern-recognise and optimise abd nodes. We should add the same operations for global isel.

  /// ABDS/ABDU - Absolute difference - Return the absolute difference between
  /// two numbers interpreted as signed/unsigned.
  /// i.e trunc(abs(sext(Op0) - sext(Op1))) becomes abds(Op0, Op1)
  ///  or trunc(abs(zext(Op0) - zext(Op1))) becomes abdu(Op0, Op1)
  ABDS,
  ABDU,

There are tests in, for example, llvm/test/CodeGen/AArch64/abd-combine.ll.
https://godbolt.org/z/71PGjf486

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: David Green (davemgreen)

SDAG, via these nodes can pattern-recognise and optimise abd nodes. We should add the same operations for global isel.

  /// ABDS/ABDU - Absolute difference - Return the absolute difference between
  /// two numbers interpreted as signed/unsigned.
  /// i.e trunc(abs(sext(Op0) - sext(Op1))) becomes abds(Op0, Op1)
  ///  or trunc(abs(zext(Op0) - zext(Op1))) becomes abdu(Op0, Op1)
  ABDS,
  ABDU,

There are tests in, for example, llvm/test/CodeGen/AArch64/abd-combine.ll.
https://godbolt.org/z/71PGjf486

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor has already been assigned to this issue. If you believe that no one is actually working on it despite an assignment, ping the person. After one week without a response, the assignee may be changed.
2. In the comments of this issue, request for it to be assigned to you, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: David Green (davemgreen)

SDAG, via these nodes can pattern-recognise and optimise abd nodes. We should add the same operations for global isel.

  /// ABDS/ABDU - Absolute difference - Return the absolute difference between
  /// two numbers interpreted as signed/unsigned.
  /// i.e trunc(abs(sext(Op0) - sext(Op1))) becomes abds(Op0, Op1)
  ///  or trunc(abs(zext(Op0) - zext(Op1))) becomes abdu(Op0, Op1)
  ABDS,
  ABDU,

There are tests in, for example, llvm/test/CodeGen/AArch64/abd-combine.ll.
https://godbolt.org/z/71PGjf486

[davemgreen]

I've added good first issue to this ticket, not because it is a small task but that it should be an interesting case that is relatively well understood that someone can attempt.

[tschuett]

First step: #118122

[aemerson]

First step: #118122

IIUC Dave added the "good first issue" label so newcomers to the project can tackle it, unless you feel like you're also a good candidate for these issues in which case go ahead and ignore.

[tschuett]

If you scroll the issue down from the top, you might notice that I opened the PR before he added the first issue label.

[tschuett]

I see myself as a newcomer. Most of my PRs are about fixing typos.

[aemerson]

If you scroll the issue down from the top, you might notice that I opened the PR before he added the first issue label.

You're right, ignore my comment then.