[PATCH] D98670: [RISCV] Pass 'half' in the lower 16 bits of an f32 value when F extension is enabled, but Zfh is not.

[Kito Cheng via Phabricator via llvm-commits]

kito-cheng added a comment.

In D98670#2658048 <https://reviews.llvm.org/D98670#2658048>, @ldrumm wrote:

> In D98670#2649998 <https://reviews.llvm.org/D98670#2649998>, @kito-cheng wrote:
>
>> I just found an issue is unrelated this patch, but related to fp16, RISC-V GCC using the traditional libgcc function name scheme like  `__extendhfdf2`(`__<op><srcT><dstT><N_OP>`) rather than `__gnu_f2h_ieee` (`__gnu_*2*_ieee`).
>>
>> Function used in GCC:
>>
>> - `__extendhfsf2` for half -> float
>> - `__truncsfhf2` for float -> half
>> - `__extendhfdf2` for double -> half
>> - `__truncdfhf2` for half -> double
>
> Yes. This was my finding as well. I taught llvm and compiler-rt about them in this patch <https://reviews.llvm.org/D84877> (unmerged). Would this be useful to revisit?

Yeah, I believe that would be very useful, and I guess we also need `__trunctfhf2` and `__extendhftf2` like https://reviews.llvm.org/D86453, calling conversion function twice while convert half to double (fp64) or long double(fp128) seems not benefit anything.

In D98670#2658048 <https://reviews.llvm.org/D98670#2658048>, @ldrumm wrote:

> In D98670#2649998 <https://reviews.llvm.org/D98670#2649998>, @kito-cheng wrote:
>
>> I just found an issue is unrelated this patch, but related to fp16, RISC-V GCC using the traditional libgcc function name scheme like  `__extendhfdf2`(`__<op><srcT><dstT><N_OP>`) rather than `__gnu_f2h_ieee` (`__gnu_*2*_ieee`).
>>
>> Function used in GCC:
>>
>> - `__extendhfsf2` for half -> float
>> - `__truncsfhf2` for float -> half
>> - `__extendhfdf2` for double -> half
>> - `__truncdfhf2` for half -> double
>
> Yes. This was my finding as well. I taught llvm and compiler-rt about them in this patch <https://reviews.llvm.org/D84877> (unmerged). Would this be useful to revisit?




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