[clang] [llvm] [mlir] IR: Promote "denormal-fp-math" to a first class attribute (PR #174293)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> > `denormal_fpenv(dynamic,dynamic float: preservesign,preservesign)`
> 
> Can we get a comma between dynamic and float? I thought this was a typo at first...

That would be a bit irregular, because the next entry isn't part of the same list. preserve-sign, preserve-sign, float aren't the same kind. It's two pairs, one with a name prefix. If there were some other separator character for the pair elements?

> Also, would it make sense to assume both elements are equal by default? Just based on looking at the tests, it seems like in practice the input and output mode are generally the same.

In general yes. It still needs to support representing both modes but it's nearly always set together (AArch64 doesn't support setting the modes separately, but x86 does)

> Do we need these flags? Can we drop them and only support attributes?

Strictly speaking, no. But it's also unpleasant to duplicate hundreds of test functions that only differ by an attribute

https://github.com/llvm/llvm-project/pull/174293