[ADT] Add APIntOps::avgfloors/avgflooru/avgceils/avgceilu

[RKSimon]

• Move implementations from SelectionDAG.cpp FoldValue into APInt.h APIntOps
  

  llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

  Lines 6024 to 6047 in deff460

  	case ISD::AVGFLOORS: {
  	unsigned FullWidth = C1.getBitWidth() + 1;
  	APInt C1Ext = C1.sext(FullWidth);
  	APInt C2Ext = C2.sext(FullWidth);
  	return (C1Ext + C2Ext).extractBits(C1.getBitWidth(), 1);
  	}
  	case ISD::AVGFLOORU: {
  	unsigned FullWidth = C1.getBitWidth() + 1;
  	APInt C1Ext = C1.zext(FullWidth);
  	APInt C2Ext = C2.zext(FullWidth);
  	return (C1Ext + C2Ext).extractBits(C1.getBitWidth(), 1);
  	}
  	case ISD::AVGCEILS: {
  	unsigned FullWidth = C1.getBitWidth() + 1;
  	APInt C1Ext = C1.sext(FullWidth);
  	APInt C2Ext = C2.sext(FullWidth);
  	return (C1Ext + C2Ext + 1).extractBits(C1.getBitWidth(), 1);
  	}
  	case ISD::AVGCEILU: {
  	unsigned FullWidth = C1.getBitWidth() + 1;
  	APInt C1Ext = C1.zext(FullWidth);
  	APInt C2Ext = C2.zext(FullWidth);
  	return (C1Ext + C2Ext + 1).extractBits(C1.getBitWidth(), 1);
  	}

• Add APIntTest unit test coverage

[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. In the comments of the issue, request for it to be assigned to you.
2. Fix the issue locally.
3. 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.
4. Create a Git commit.
5. Run git clang-format HEAD~1 to format your changes.
6. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation.

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)

- [ ] Move implementations from SelectionDAG.cpp FoldValue into APInt.h APIntOps https://github.com/llvm/llvm-project/blob/deff460b46dfcc8d6d5917a2b78c0d52edbe4afb/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp#L6024-L6047 - [ ] Add APIntTest unit test coverage

[Atousa]

@RKSimon I am interested in working on this issue. Please assign it to me.

[EugeneZelenko]

@Atousa: Just create pull request and mention it on this page.