[llvm] [LLVM][CodeGen][SVE] Only use unpredicated bfloat instructions when all lanes are in use. (PR #168387)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

I have been following the floating point environment support for a while although kind of lost track since https://github.com/llvm/llvm-project/pull/109798 stalled.  The constrained intrinsic approach is not a viable implementation for target intrinsics, with ongoing work to redesign/replace/reimplement them using operand bundles. A previous attempt of mine to guide selection using a function's strict-fp attribute was rejected.

I do need to extend the SVE support for the STRICT_* ISD nodes, but today they simply lower to their non-strict counterparts. When combined with the above issues, we chose to at least not aggravate the issue with a minimal effect on code generation given the required predicate is likely always available.

https://github.com/llvm/llvm-project/pull/168387