[PATCH v6] Add support for SoftFloat library on ARM (original) (raw)

Jakub Vaněk linuxtardis at gmail.com
Thu Dec 13 13:21:30 UTC 2018

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 reinterpretcast 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 reinterpretcast 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 softfloatarm.cpp. > >> If type cast is the only reason why don't you use reinterpretcast? > >> > >> regards, > >> Boris > > I'm using memcpy there because float32t is a struct containing a > > single uint32t 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: JVMLDFLAGSFEATURES += > -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 > >>> > > >>> >

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