[PATCH v6] Add support for SoftFloat library on ARM

[Boris Ulasevich]

Hi Jakub,

I was in doubt about SoftFloat licence if it is correct to add it
to OpenJDK, so I consulted to Oracle, and answer is that
license (mark down) file should not be in the OpenJDK sources
because library codes are not included in the OpenJDK sources.
So please remove softfloat.md.

Thanks,
Boris

On 13.12.2018 16:39, Jakub Vaněk wrote:
> Hmm, the patch still fails. I will have to redo the changes
> in the source tree and then reexport the patch. Editing
> the patch file manually wasn't a good idea.
> 
> Thanks,
> 
> Jakub
> 
> čt 13. 12. 2018 v 14:21 odesílatel Jakub Vaněk <linuxtardis at gmail.com> napsal:
>>
>> Hi,
>>
>> I have made a mistake when editing the patch (I forgot to change the
>> added line count in one header).
>>
>> https://raw.githubusercontent.com/ev3dev-lang-java/openjdk-ev3/52d38ea739fda826759f171313991717e477c31d/upstream/softfloat.patch
>>
>> Thanks,
>>
>> Jakub
>>
>> čt 13. 12. 2018 v 14:10 odesílatel Jakub Vaněk <linuxtardis at gmail.com> napsal:
>>>
>>> Hi Boris,
>>>
>>> I have updated the patch:
>>> https://raw.githubusercontent.com/ev3dev-lang-java/openjdk-ev3/0887015e0dfcc45ffed03872a8ad42a609496459/upstream/softfloat.patch
>>>
>>> Now reinterpret_cast is used and the URL is present
>>> only in the documentation for enabling flags.
>>>
>>> I didn't expect a performance penalty, I have seen
>>> somewhere that compilers are nowadays good in
>>> seeing through this type of operation:
>>> https://blog.regehr.org/archives/959
>>>
>>> I tried compiling a similar code (with noinline functions)
>>> on https://godbolt.org/ and on GCC >= 4.6.4 memcpy is
>>> optimized away even on -O0.
>>>
>>> However I agree that the reinterpret_cast way is more
>>> readable and conscise.
>>>
>>> Thanks,
>>>
>>> Jakub
>>>
>>> čt 13. 12. 2018 v 9:11 odesílatel Boris Ulasevich
>>> <boris.ulasevich at bell-sw.com> napsal:
>>>>
>>>> Hi Jakub,
>>>>
>>>> Please see comments inline.
>>>> And one more point: please remove links to mail threads from sources (http://mail.openjdk.java.net/pipermail/aarch32-port-dev/2016-November/000611.html).
>>>>
>>>> Boris
>>>>
>>>> 12.12.2018 17:36, Jakub Vaněk пишет:
>>>>> Hi Erik,
>>>>>
>>>>> On 2018-12-12 at 15:41 +0300, Boris Ulasevich wrote:
>>>>>> Hi Jakub,
>>>>>>
>>>>>> I do not understand why you use memcpy in softfloat_arm.cpp.
>>>>>> If type cast is the only reason why don't you use reinterpret_cast?
>>>>>>
>>>>>> regards,
>>>>>> Boris
>>>>> I'm using memcpy there because float32_t is a struct containing a
>>>>> single uint32_t member. I think that the proper way of doing a byte-
>>>>> level conversion between different types (type punning) is via memcpy.
>>>> Do not you expect performance penalty using type conversion this way?
>>>>> If I used a casted pointer, this would violate the rule that I can
>>>>> access a memory location through a pointer of only one type.
>>>>
>>>> -fno-strict-aliasing gcc option is used to disable compiler complains on
>>>> this rule:
>>>>
>>>> jdk-jdk/make/hotspot/lib/JvmFeatures.gmk:  JVM_LDFLAGS_FEATURES +=
>>>> -fno-strict-aliasing
>>>>
>>>>> Using
>>>>> union for this seems to be also undefined in C++, as then I would
>>>>> access the value through a non-active member.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Jakub
>>>>>
>>>>>> On 10.12.2018 23:23, Jakub Vaněk wrote:
>>>>>>> Hi Erik,
>>>>>>>
>>>>>>> On 2018-12-10 at 09:39 -0800, Erik Joelsson wrote:
>>>>>>>> The build changes look ok to me.
>>>>>>>>
>>>>>>>> I do think --enable-softfloat is redundant as using any of the
>>>>>>>> other
>>>>>>>> parameters would imply it to be set, but it's ok to have it
>>>>>>>> there.
>>>>>>> Thanks for the review. The motivation for this was that I was
>>>>>>> closely
>>>>>>> following how libffi is handled. The enable option was a workaround
>>>>>>> for
>>>>>>> the detection of softfloat in system paths. I don't think this is
>>>>>>> how
>>>>>>> the library is going to be used, so I removed this option.
>>>>>>>
>>>>>>> New patch can be found here:
>>>>>>> https://github.com/ev3dev-lang-java/openjdk-ev3/blob/78a9d35986ed51273d9a3bb9878cbfcbe2488bfb/upstream/softfloat.patch
>>>>>>>
>>>>>>> Regards,
>>>>>>>
>>>>>>> Jakub
>>>>>>>
>>>>>>>> /Erik
>>>>>>> < raw patch at
>>>>>>> https://raw.githubusercontent.com/ev3dev-lang-java/openjdk-ev3/78a9d35986ed51273d9a3bb9878cbfcbe2488bfb/upstream/softfloat.patch
>>>>>>>    >
>>>>>>>
>>>>