[llvm] [X86] Report an error for FP environment accesses that are not 256 bits (PR #228841)

[Doha Nam via llvm-commits]

waroad wrote:

Thanks! I couldn't find a generic place that knows the expected FP env size. TargetLowering has no hook for it, so generic code can't tell that i64 is wrong (the fegetenv libcall path seems to have the same problem, since the stack temporary is sized from the IR type). Would a TLI hook for the FP env size, checked in SelectionDAGBuilder, be OK? X86 would return 256. Happy to rework.

https://github.com/llvm/llvm-project/pull/228841