[llvm] CodeGen: Add -denormal-fp-math-bf16 flag (PR #90425)

[Freddy Ye via llvm-commits]

FreddyLeaf wrote:

> Is it all the operations, or just these specific dot products? Are there specific bf16<->float conversions that have the same issue? What about basic arithmetic operations?

x86 only supports bf16<->conversion and this dot production operations. float->bf16 instruction also mentioned this in SDM but bf16->float didn't. but it still mentioned does not consult or update MXCSR so I suppose it won't flush to zero as well since it required consulting MXCSR.

https://github.com/llvm/llvm-project/pull/90425