[X86] X86TTIImpl::instCombineIntrinsic - attempt to use llvm::computeKnownFPClass to generalise SSE/AVX FP scalar MAX/MIN intrinsics

[RKSimon]

Followup to #173270, with suitable DemandedElts masks we can handle the scalar intrinsics:

x86_sse_max_ss
x86_sse_min_ss
x86_sse2_max_sd
x86_sse2_min_sd

However, these will require special expansion to 2*extractelement/maxnum/insertelement as only the lowest element is actually called and the upper elements are passed through from the first operand:
https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_max_ss&ig_expand=4391,4391

[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-good-first-issue

Author: Simon Pilgrim (RKSimon)

Details

Followup to #173270, with suitable DemandedElts masks we can handle the scalar intrinsics: ``` x86_sse_max_ss x86_sse_min_ss x86_sse2_max_sd x86_sse2_min_sd ``` However, these will require special expansion to 2*extractelement/maxnum/insertelement as only the lowest element is actually called and the upper elements are passed through from the first operand: https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_max_ss&ig_expand=4391,4391

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Details

Followup to #173270, with suitable DemandedElts masks we can handle the scalar intrinsics: ``` x86_sse_max_ss x86_sse_min_ss x86_sse2_max_sd x86_sse2_min_sd ``` However, these will require special expansion to 2*extractelement/maxnum/insertelement as only the lowest element is actually called and the upper elements are passed through from the first operand: https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_max_ss&ig_expand=4391,4391

[guiolidc]

Hi @RKSimon , could i work on this issue?

[calm329]

I'd love to work on this issue