[AArch64] AArch64TargetLowering::computeKnownBitsForTargetNode - add support for AArch64ISD::MOV/MVN constants

[RKSimon]

Followup to #148596

AArch64TargetLowering::computeKnownBitsForTargetNode is still missing for the following constant nodes:

  case AArch64ISD::MOVIedit:
  case AArch64ISD::MOVImsl:
  case AArch64ISD::MVNIshift:
  case AArch64ISD::MVNImsl:

As its tricky to get codegen folds to consistently use these, it might be easiest to add test coverage to AArch64SelectionDAGTest.cpp (there are already some computeKnownBits tests in there) - adding unit test coverage for the existing AArch64ISD::MOVI and AArch64ISD::MOVIshift handling would be useful there as well.

CC @aabhinavg1

[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.
2. Leave a comment indicating that you are working on the issue, 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-backend-aarch64

Author: Simon Pilgrim (RKSimon)

Followup to #148596

AArch64TargetLowering::computeKnownBitsForTargetNode is still missing for the following constant nodes:

  case AArch64ISD::MOVIedit:
  case AArch64ISD::MOVImsl:
  case AArch64ISD::MVNIshift:
  case AArch64ISD::MVNImsl:

As its tricky to get codegen folds to consistently use these, it might be easiest to add test coverage to AArch64SelectionDAGTest.cpp (there are already some computeKnownBits tests in there) - adding unit test coverage for the existing AArch64ISD::MOVI and AArch64ISD::MOVIshift handling would be useful there as well.

CC @aabhinavg1

[llvmbot]

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

Author: Simon Pilgrim (RKSimon)

Followup to #148596

AArch64TargetLowering::computeKnownBitsForTargetNode is still missing for the following constant nodes:

  case AArch64ISD::MOVIedit:
  case AArch64ISD::MOVImsl:
  case AArch64ISD::MVNIshift:
  case AArch64ISD::MVNImsl:

As its tricky to get codegen folds to consistently use these, it might be easiest to add test coverage to AArch64SelectionDAGTest.cpp (there are already some computeKnownBits tests in there) - adding unit test coverage for the existing AArch64ISD::MOVI and AArch64ISD::MOVIshift handling would be useful there as well.

CC @aabhinavg1

[ningxinr]

@RKSimon I'd like to try this one! Can you assign it to me? Thanks!

[RKSimon]

Reverted in 7d26150