[PATCH] libgccjit: Handle truncation and extension for casts [PR 95498]

[Martin Liška]

@David: PING

On 2/20/21 11:17 PM, Antoni Boucher via Gcc-patches wrote:
> Hi.
> Thanks for your feedback!
> 
> See answers below:
> 
> On Sat, Feb 20, 2021 at 11:20:35AM -0700, Tom Tromey wrote:
>>>>>>> "Antoni" == Antoni Boucher via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
>>
>> Antoni> gcc/jit/
>> Antoni>     PR target/95498
>> Antoni>     * jit-playback.c: Add support to handle truncation and extension
>> Antoni>     in the convert function.
>>
>> Antoni> +  switch (dst_code)
>> Antoni> +    {
>> Antoni> +    case INTEGER_TYPE:
>> Antoni> +    case ENUMERAL_TYPE:
>> Antoni> +      t_ret = convert_to_integer (dst_type, expr);
>> Antoni> +      goto maybe_fold;
>> Antoni> +
>> Antoni> +    default:
>> Antoni> +      gcc_assert (gcc::jit::active_playback_ctxt);
>> Antoni> +      gcc::jit::active_playback_ctxt->add_error (NULL, "unhandled conversion");
>> Antoni> +      fprintf (stderr, "input expression:\n");
>> Antoni> +      debug_tree (expr);
>> Antoni> +      fprintf (stderr, "requested type:\n");
>> Antoni> +      debug_tree (dst_type);
>> Antoni> +      return error_mark_node;
>> Antoni> +
>> Antoni> +    maybe_fold:
>> Antoni> +      if (TREE_CODE (t_ret) != C_MAYBE_CONST_EXPR)
>> Antoni> +    t_ret = fold (t_ret);
>> Antoni> +      return t_ret;
>>
>> It seems weird to have a single 'goto' to maybe_fold, especially inside
>> a switch like this.
>>
>> If you think the maybe_fold code won't be reused, then it should just be
>> hoisted up and the 'goto' removed.
> 
> This actually depends on how the support for cast between integers and pointers will be implemented (see below).
> If we will support truncating pointers (does that even make sense? and I guess we cannot extend a pointer unless we add the support for uint128_t), that label will be reused for that case.
> Otherwise, it might not be reused.
> 
> So, please tell me which option to choose and I'll update my patch.
> 
>> On the other hand, if the maybe_fold code might be reused for some other
>> case, then I suppose I would have the case end with 'break' and then
>> have this code outside the switch.
>>
>>
>> In another message, you wrote:
>>
>> Antoni> For your question, the current code already works with boolean and
>> Antoni> reals and casts between integers and pointers is currently not
>> Antoni> supported.
>>
>> I am curious why this wasn't supported.  It seems like something that
>> one might want to do.
> 
> I have no idea as this is my first contribution to gcc.
> But this would be indeed very useful and I opened an issue about this: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95438
> 
>> thanks,
>> Tom
> 
> Thanks!