[crossgen2] Handle Floor and Ceiling

[cshung]

dotnet/coreclr#26982 (comment)

[4creators]

Is it possible to provide a description of the problem and software architecture associated with it? It would make the issue understandable to all coreclr contributors.

[cshung]

Is it possible to provide a description of the problem and software architecture associated with it? It would make the issue understandable to all coreclr contributors.

This issue is created to track the work required to address one of these work items mentioned as a comment in my pull request.

dotnet/coreclr#26982 (comment)

The pull request was created as a cherry-pick of 6ec78980083123ec82300cbcbaadbb34fd34ea0a, which is a port of these 3 pull requests (#24689, dotnet/coreclr#24917, dotnet/coreclr#25365). As I understand it, the original pull request allow crossgen to use hardware intrinsics. The port was intended to allow crossgen2 to also use hardware intrinsics.

To be brutally honest, I don't actually understand what the problem is, at least not in a clearly reproducible manner. The comment must have written to make sure certain scenarios will not fail. I have yet to figure out what those scenarios are.

@MichalStrehovsky who authored the original pull requests and the original comment should be able to explain in detail what the problem is.

The pull request I submitted above as an attempt to fix this issue was a blind port of the changes, I don't know what the problem was, I don't know if it actually fixed the problem or not. I hope it does.

[MichalStrehovsky]

This is specifically about part of dotnet/coreclr#25365 crossgen fix that should have been ported to crossgen2, but wasn't. The issue linked from the pull request has the details (basically, since we allow RyuJIT to use SSE41, RyuJIT is free to use SSE41 in expansion of Round/Floor/Ceiling). Expanding Round/Floor/Ceiling is not what we intended to enable (we only intended to enable SSE41 on the SSE41 intrinsic class that is supposed to guard all use of the intrinsics with an SSE41.IsSupported check - Math.Round is not guareded by SSE41.IsSupported).

I hope this clarifies things.