On Mon, 25 Sep 2023, Sylvain Noiry via Gcc wrote:

> --> Idea: Add an attribute to the Tree complex type which specify pure real /
> pure
>    imaginary / full complex ?

If you start from the implementation approach of lowering imaginary type 
operations in the front end, a flag on a REAL_TYPE would seem natural (and 
then the rest of the compiler could treat such types the same as other 
real types with the same machine modes).

That would however mean that e.g. conversions to/from imaginary types in 
the front end are not the same thing as what you get from middle-end 
conversions (the former would apply the rules that converting imaginary to 
real or real to imaginary produces zero while preserving side effects from 
the expression converted; the latter would be a no-op conversion if the 
machine modes are the same), which has the potential to be confusing.

-- 
Joseph S. Myers
joseph@codesourcery.com