[PATCH][X86] Add ISel patterns to select 'fp32_to_fp16' and 'fp16_to_fp32' dag nodes.

[Andrea Di Biagio]

Do you think it would it be ok if I just remove the check for soft-float?


On Fri, Jun 20, 2014 at 11:29 PM, Andrea Di Biagio
<andrea.dibiagio at gmail.com> wrote:
> Hi Jim,
>
> On Fri, Jun 20, 2014 at 9:32 PM, Jim Grosbach <grosbach at apple.com> wrote:
>> I agree calling library helpers is the correct fallback here.
>>
>> What’s the behavior with soft-float? Specifically,
>>
>> +  if (!TM.Options.UseSoftFloat && !Subtarget->hasF16C()) {
>
> I have just run some tests (using the test-case from this patch)
> with/without flag -float-abi=soft/hard.
> The presence/absence of that flag doesn't seem to affect the output.
>
> My originally idea was to generate library calls for
> float-to-half-float conversions if 'soft' float-abi was specified.
> I thought that the presence of that flag would have affected the
> codegen for those dag nodes. But apparently I was wrong.
>
>>
>> -Jim
>>
>>> On Jun 19, 2014, at 6:53 AM, Andrea Di Biagio <andrea.dibiagio at gmail.com> wrote:
>>>
>>> Hi,
>>>
>>> this patch:
>>> 1) Adds tablegen patterns to select F16C float-to-half-float
>>> conversion instructions (and vice versa) from 'f32_to_f16' (and
>>> 'f16_to_f32') dag nodes;
>>>
>>> 2) Teaches the backend how to emit compiler runtime library call to
>>> __gnu_f2h_ieee and __gnu_h2f_ieee if there is no F16C support.
>>>
>>> About point 2.
>>> I am not sure if there is a better ways to fix/workaround this
>>> problem. In general, my opinion is that the backend shouldn't raise a
>>> error if we don't have F16C and the DAG contains
>>> 'f32_to_f16/f16_to_f32' nodes.
>>>
>>> The compiler already knows about the existence of libcalls
>>> '__gnu_f2h_ieee' and '__gnu_h2f_ieee2' (see TargetLoweringBase.cpp).
>>> So, my idea (if you agree) is to generate runtime calls instead of
>>> returning an ISel error.
>>> However, this could result later on in a linker error if the runtime
>>> library doesn't define '__gnu_f2h_ieee' and '__gnu_h2f_ieee'.
>>>
>>> Please let me know what you think.
>>>
>>> Thanks!
>>> Andrea Di Biagio
>>> <patch-f16c-conv.diff>
>>