[PATCH] libgccjit: Improve doc and comments regarding type casts (Was: Clarifying the permitted type conversions)

[Andrea Corallo]

Alex Coplan <Alex.Coplan@arm.com> writes:

> Secondly, I wanted to clarify the situation with respect to explicit
> casts; that is, those conversions allowed by gcc_jit_context_new_cast().
> The docs [0] say:
>
> Currently only a limited set of conversions are possible:
>  - int <-> float
>  - int <-> bool
>  - P* <-> Q*, for pointer types P and Q
>
> However, empirically (at least on aarch64), libgccjit appears to allow
> me to compile casts between any pair of types in the following set
> without any complaint:
>
> {
>   SIGNED_CHAR,
>   UNSIGNED_CHAR,
>   SHORT,
>   UNSIGNED_SHORT,
>   INT,
>   UNSIGNED_INT,
>   LONG,
>   UNSIGNED_LONG,
>   LONG_LONG,
>   UNSIGNED_LONG_LONG
> }

Hi Alex,

Looking at the code I believe all these casts are meant to be supported
(read your intuition was correct).

Also IMO source of confusion is that the doc is mentioning 'int' and
'float' but I believe would be better to have like 'integral' and
'floating-point' to clearly disambiguates with respect to the C
types.

AFAIU the set of supported casts should be like:

     integral       <-> integral
     floating-point <-> floating-point
     integral       <-> floating-point
     integral       <-> bool
     P*             <-> Q*   for pointer types P and Q.

I'd propose to install the following patch to make doc and comments
homogeneous at documenting what do we accept, and I guess we should just
consider bugs if some of these conversions is not handled correctly or
leads to ICE.

Bests

  Andrea

gcc/jit/ChangeLog

2020-07-21  Andrea Corallo  <andrea.corallo@arm.com>

	* docs/_build/texinfo/libgccjit.texi (Type-coercion): Improve doc
	on allowed type casting.
	* docs/topics/expressions.rst (gccjit::context::new_cast)
	(gcc_jit_context_new_cast): Likewise.
	* libgccjit.c: Improve comment on allowed type casting.
	* libgccjit.h: Likewise

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