[AArch64] AArch64TargetLowering::computeKnownBitsForTargetNode - add support for AArch64ISD::MOVIshift

[RKSimon]

Only AArch64ISD::MOVI is currently handled, preventing later value tracking based folds from recognizing lowered constants

I don't know much about these nodes, but all of these might be eventual candidates forAArch64TargetLowering::computeKnownBitsForTargetNode:

  case AArch64ISD::MOVI:
  case AArch64ISD::MOVIshift:
  case AArch64ISD::MOVIedit:
  case AArch64ISD::MOVImsl:
  case AArch64ISD::MVNIshift:
  case AArch64ISD::MVNImsl:

Noticed while trying to triage #148191

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: Simon Pilgrim (RKSimon)

Only AArch64ISD::MOVI is currently handled, preventing later value tracking based folds from recognizing lowered constants

I don't know much about these nodes, but all of these might be eventual candidates forAArch64TargetLowering::computeKnownBitsForTargetNode:

  case AArch64ISD::MOVI:
  case AArch64ISD::MOVIshift:
  case AArch64ISD::MOVIedit:
  case AArch64ISD::MOVImsl:
  case AArch64ISD::MVNIshift:
  case AArch64ISD::MVNImsl:

Noticed while trying to triage #148191

[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 is working on this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
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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: Simon Pilgrim (RKSimon)

Only AArch64ISD::MOVI is currently handled, preventing later value tracking based folds from recognizing lowered constants

I don't know much about these nodes, but all of these might be eventual candidates forAArch64TargetLowering::computeKnownBitsForTargetNode:

  case AArch64ISD::MOVI:
  case AArch64ISD::MOVIshift:
  case AArch64ISD::MOVIedit:
  case AArch64ISD::MOVImsl:
  case AArch64ISD::MVNIshift:
  case AArch64ISD::MVNImsl:

Noticed while trying to triage #148191

[RKSimon]

@aabhinavg1 I have a patch for this if you haven't looked at it yet.

[aabhinavg1]

@RKSimon!

I had just started looking into the issue and was planning to explore possible additions for MOVIshift. If you already have a patch ready, feel free to proceed I’ll step back on this one and look for another good first issue instead.

Appreciate the guidance!

[aabhinavg1]

@RKSimon! I looked into your patch it covers AArch64ISD::MOVIshift, which is great.

I noticed there are other similar cases like:

• AArch64ISD::MOVIedit
• AArch64ISD::MOVImsl
• AArch64ISD::MVNIshift
• AArch64ISD::MVNImsl

Would it be okay if I explored and submitted a follow-up patch to handle these additional cases in computeKnownBitsForTargetNode?