dmd Arm64 - first function compile!

[Guillaume Piolat]

On Sunday, 2 June 2024 at 06:30:18 UTC, Walter Bright wrote:
> And there it is! Nothing else works, but what the heck.
>
> https://github.com/WalterBright/dmd/commit/04546a8f72c10a09764f23675c67c5fbdf29628c

A few oddities in "arm64":

- Some arm64 archs can't represent a NaN with a negative sign. 
But Apple version of arm64 can.

- Floating-point to integer casting tend to clamp to min/max 
representable integers, when the float value exceed the integer 
representation. IIRC D doesn't define the maximum values for 
which this is a well defined operation.

- Likewise, shifting by more bits then the integer has is well 
defined, and doesn't work the same as in x86. So I'd say this is 
generally UB in D.

- Rounding a float that is exactly in the middle (such as 3.5) is 
a bit different than x86 IIRC, the rules are slightly different 
but I think this was only arm32.

- the denormal flags are one flag (instead of two in x86)