*ping* / Re: [LTO] PR 86416 – improve lto1 diagnostic if a mode does not exist (esp. for offloading targets)

[Tobias Burnus]

*ping*

On 12/13/19 3:34 PM, Tobias Burnus wrote:
> As long as one compiles for a single target, the message is unlikely 
> to appear.
>
> However, when compiling for offloading, the modes supported on the target
> 'host' and on the target 'device' can be different. In particular,
> 'long double' (when larger than double) and '__float128' might not be
> available on the device.
>
> This gives currently errors like the following (see PR, comment 0):
>
>> lto1: fatal error: unsupported mode TF
>> compilation terminated.
>> mkoffload: fatal error:
>> x86_64-pc-linux-gnu-accel-nvptx-none-gcc returned 1 exit status 
>
> While the device target is hidden in 
> 'x86_64-pc-linux-gnu-accel-nvptx-none-gcc', it might make more sense 
> to add it more prominently. Additionally, an average user does
> not understand what 'TF' or 'XF' means.
>
> Solutions:
> (A) Add the target to the output
> (B) Add a better description for the error
>
> I did both in the attached patch, giving:
> lto1: fatal error: nvptx-none - 80-bit floating-point numbers 
> unsupported (mode 'XF')
> lto1: fatal error: nvptx-none - 128-bit floating-point numbers 
> unsupported (mode 'TF')
>
> * (A) should be fine, I think.
>
> * But I am not 100% happy with (B). I think as interim solution,
> it is acceptable as XF/TF are well defined and probably the most
> common problem. — Alternatively, one could only commit (A) or
> solve it more properly (how?).
>
> * If, e.g., 'long long' or 'integer(kind=16)' are used, only a
> generic message is printed.  A message such as "'__float128' not
> supported" or "'real(kind=10)' not supported" is more helpful and
> supporting all modes and not cherry picking those two would be
> useful as well.
>
> The question is how to pass this information to lto-streamer-in.c;
> it is available as TYPE_NAME – and, with debugging turned on, this
> also gets passed on, but is also not be readily available in
> lto_input_mode_table. – Suggestions?
>
>
> Build on x86-64-gnu-linux and tested without offloading and with nvptx
> offloading.
>
> Tobias
>