The pointers must always be i8* the alignment is independent and is controlled by the attributes on the arguments in the call to memcpy. ~Craig On Mon, Jan 29, 2018 at 11:45 PM, ma jun <jun.parser at gmail.com> wrote:> Hi > > > 2018-01-30 15:36 GMT+08:00 ma jun <jun.parser at gmail.com>: > >> Hi >> Thanks ! >> so for this example >> void foo(X &src, X &dst) { >> dst = src; >> } >> and the IR: >> >> define void @foo(X&, X&)(%struct.X* dereferenceable(8), %struct.X* >> dereferenceable(8)) #0 { >> %3 = alloca %struct.X*, align 8 >> %4 = alloca %struct.X*, align 8 >> store %struct.X* %0, %struct.X** %3, align 8 >> store %struct.X* %1, %struct.X** %4, align 8 >> %5 = load %struct.X*, %struct.X** %3, align 8 >> %6 = load %struct.X*, %struct.X** %4, align 8 >> %7 = bitcast %struct.X* %6 to i8* >> %8 = bitcast %struct.X* %5 to i8* >> call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %7, i8* align 4 %8, >> i64 8, i1 false) >> > > also since the dst and src are 4 byte align , can we use the IR below: > > %7 = bitcast %struct.X* %6 to i32* > > %8 = bitcast %struct.X* %5 to i32* > > call void @llvm.memcpy.p0i32.p0i32.i64(i32* align 4 %7, i32* align 4 %8, > i64 8, i1 false) > > >> ret void >> } >> >> how can I transform the llvm.memcpy into data move loop IR and eliminate >> the bitcast instruction ? >> >> Regards >> Jun >> >> >> 2018-01-30 15:24 GMT+08:00 Craig Topper <craig.topper at gmail.com>: >> >>> The i8 type in the pointers doesn't matter a whole lot. There's a long >>> term plan to remove the type from all pointers in llvm IR. >>> >>> Yes, clang will use memcpy for struct copies. You can see example IR >>> here https://godbolt.org/g/8gQ18m. You'll see that the struct pointers >>> are bitcasted to i8* before the call. >>> >>> ~Craig >>> >>> On Mon, Jan 29, 2018 at 11:12 PM, ma jun via llvm-dev < >>> llvm-dev at lists.llvm.org> wrote: >>> >>>> >>>> Hi all >>>> I'm new here, and I have some question about llvm.memcpy intrinsic. >>>> why does llvm.memcpy intrinsic only support i8* for first two >>>> arguments? and does clang will also transform struct copy into llvm.memcpy >>>> ? what format does IR looks like? >>>> Thanks ! >>>> >>>> Regards >>>> Jun >>>> >>>> >>>> _______________________________________________ >>>> LLVM Developers mailing list >>>> llvm-dev at lists.llvm.org >>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >>>> >>>> >>> >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20180130/60309330/attachment.html>
Hi Craig
Thank you very much ！
2018-01-30 16:11 GMT+08:00 Craig Topper <craig.topper at gmail.com>:
> The pointers must always be i8* the alignment is independent and is
> controlled by the attributes on the arguments in the call to memcpy.
>
> ~Craig
>
> On Mon, Jan 29, 2018 at 11:45 PM, ma jun <jun.parser at gmail.com>
wrote:
>
>> Hi
>>
>>
>> 2018-01-30 15:36 GMT+08:00 ma jun <jun.parser at gmail.com>:
>>
>>> Hi
>>> Thanks !
>>> so for this example
>>> void foo(X &src, X &dst) {
>>> dst = src;
>>> }
>>> and the IR:
>>>
>>> define void @foo(X&, X&)(%struct.X* dereferenceable(8),
%struct.X*
>>> dereferenceable(8)) #0 {
>>> %3 = alloca %struct.X*, align 8
>>> %4 = alloca %struct.X*, align 8
>>> store %struct.X* %0, %struct.X** %3, align 8
>>> store %struct.X* %1, %struct.X** %4, align 8
>>> %5 = load %struct.X*, %struct.X** %3, align 8
>>> %6 = load %struct.X*, %struct.X** %4, align 8
>>> %7 = bitcast %struct.X* %6 to i8*
>>> %8 = bitcast %struct.X* %5 to i8*
>>> call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %7, i8* align 4
%8,
>>> i64 8, i1 false)
>>>
>>
>> also since the dst and src are 4 byte align , can we use the IR below:
>>
>> %7 = bitcast %struct.X* %6 to i32*
>>
>> %8 = bitcast %struct.X* %5 to i32*
>>
>> call void @llvm.memcpy.p0i32.p0i32.i64(i32* align 4 %7, i32* align 4
%8,
>> i64 8, i1 false)
>>
>>
>>> ret void
>>> }
>>>
>>> how can I transform the llvm.memcpy into data move loop IR and
>>> eliminate the bitcast instruction ?
>>>
>>> Regards
>>> Jun
>>>
>>>
>>> 2018-01-30 15:24 GMT+08:00 Craig Topper <craig.topper at
gmail.com>:
>>>
>>>> The i8 type in the pointers doesn't matter a whole lot.
There's a long
>>>> term plan to remove the type from all pointers in llvm IR.
>>>>
>>>> Yes, clang will use memcpy for struct copies. You can see
example IR
>>>> here https://godbolt.org/g/8gQ18m. You'll see that the
struct pointers
>>>> are bitcasted to i8* before the call.
>>>>
>>>> ~Craig
>>>>
>>>> On Mon, Jan 29, 2018 at 11:12 PM, ma jun via llvm-dev <
>>>> llvm-dev at lists.llvm.org> wrote:
>>>>
>>>>>
>>>>> Hi all
>>>>> I'm new here, and I have some question about
llvm.memcpy
>>>>> intrinsic.
>>>>> why does llvm.memcpy intrinsic only support i8* for
first two
>>>>> arguments? and does clang will also transform struct copy
into llvm.memcpy
>>>>> ? what format does IR looks like?
>>>>> Thanks !
>>>>>
>>>>> Regards
>>>>> Jun
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
>>>>>
>>>>
>>>
>>
>
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Jakub (Kuba) Kuderski via llvm-dev
2018-Jan-31 17:36 UTC
[llvm-dev] llvm.memcpy for struct copy
Hi Ma, how can I transform the llvm.memcpy into data move loop IR and eliminate> the bitcast instruction ? >I'm not sure why you are concerned about memcpy and bitcasts, but if you call MCpyInst->getSource() and MCpyInst->getDest() it will look through casts and give you the 'true' source/destination. If you want to get rid of memcpy altogether, you can take a look at this pass: https://github.com/seahorn/seahorn/blob/master/lib/Transforms/Scalar/PromoteMemcpy.cc . Best, Kuba On Tue, Jan 30, 2018 at 3:22 AM, ma jun via llvm-dev < llvm-dev at lists.llvm.org> wrote:> Hi Craig > Thank you very much ！ > > 2018-01-30 16:11 GMT+08:00 Craig Topper <craig.topper at gmail.com>: > >> The pointers must always be i8* the alignment is independent and is >> controlled by the attributes on the arguments in the call to memcpy. >> >> ~Craig >> >> On Mon, Jan 29, 2018 at 11:45 PM, ma jun <jun.parser at gmail.com> wrote: >> >>> Hi >>> >>> >>> 2018-01-30 15:36 GMT+08:00 ma jun <jun.parser at gmail.com>: >>> >>>> Hi >>>> Thanks ! >>>> so for this example >>>> void foo(X &src, X &dst) { >>>> dst = src; >>>> } >>>> and the IR: >>>> >>>> define void @foo(X&, X&)(%struct.X* dereferenceable(8), %struct.X* >>>> dereferenceable(8)) #0 { >>>> %3 = alloca %struct.X*, align 8 >>>> %4 = alloca %struct.X*, align 8 >>>> store %struct.X* %0, %struct.X** %3, align 8 >>>> store %struct.X* %1, %struct.X** %4, align 8 >>>> %5 = load %struct.X*, %struct.X** %3, align 8 >>>> %6 = load %struct.X*, %struct.X** %4, align 8 >>>> %7 = bitcast %struct.X* %6 to i8* >>>> %8 = bitcast %struct.X* %5 to i8* >>>> call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %7, i8* align 4 %8, >>>> i64 8, i1 false) >>>> >>> >>> also since the dst and src are 4 byte align , can we use the IR below: >>> >>> %7 = bitcast %struct.X* %6 to i32* >>> >>> %8 = bitcast %struct.X* %5 to i32* >>> >>> call void @llvm.memcpy.p0i32.p0i32.i64(i32* align 4 %7, i32* align 4 %8 >>> , i64 8, i1 false) >>> >>> >>>> ret void >>>> } >>>> >>>> how can I transform the llvm.memcpy into data move loop IR and >>>> eliminate the bitcast instruction ? >>>> >>>> Regards >>>> Jun >>>> >>>> >>>> 2018-01-30 15:24 GMT+08:00 Craig Topper <craig.topper at gmail.com>: >>>> >>>>> The i8 type in the pointers doesn't matter a whole lot. There's a long >>>>> term plan to remove the type from all pointers in llvm IR. >>>>> >>>>> Yes, clang will use memcpy for struct copies. You can see example IR >>>>> here https://godbolt.org/g/8gQ18m. You'll see that the struct >>>>> pointers are bitcasted to i8* before the call. >>>>> >>>>> ~Craig >>>>> >>>>> On Mon, Jan 29, 2018 at 11:12 PM, ma jun via llvm-dev < >>>>> llvm-dev at lists.llvm.org> wrote: >>>>> >>>>>> >>>>>> Hi all >>>>>> I'm new here, and I have some question about llvm.memcpy >>>>>> intrinsic. >>>>>> why does llvm.memcpy intrinsic only support i8* for first two >>>>>> arguments? and does clang will also transform struct copy into llvm.memcpy >>>>>> ? what format does IR looks like? >>>>>> Thanks ! >>>>>> >>>>>> Regards >>>>>> Jun >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> LLVM Developers mailing list >>>>>> llvm-dev at lists.llvm.org >>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >>>>>> >>>>>> >>>>> >>>> >>> >> > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev > >-- Jakub Kuderski -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20180131/9bcc9fec/attachment.html>