llvm dev - Sep 2017 - VMOVNTDQ in LLVM

Hello, i am using llvm 4.0 i am generating intel avx code. But in code i
dont find VMOVNTDQ instruction. Why is that so? When does this instruction
generated?


Please clarify.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20170928/9e34fd82/attachment-0001.html>

What code did you write where you expected VMOVNTDQ to be generated?

The x86 MOVNT instructions are something of an attractive nuisance. There are
cases where they are beneficial, but those cases are much less common and harder
to characterize than you might expect. LLVM is deliberately conservative about
using MOVNT (IIRC it’s currently only generated if you explicitly ask for it by
using intrinsics).

– Steve
> On Sep 28, 2017, at 9:10 AM, hameeza ahmed via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hello, i am using llvm 4.0 i am generating intel avx code. But in code i
dont find VMOVNTDQ instruction. Why is that so? When does this instruction
generated?
> 
> 
> Please clarify.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

This thread from last year has some additional detail regarding the hazards of
aggressive MOVNT generation if you’re interested:

http://lists.llvm.org/pipermail/llvm-dev/2016-May/098980.html
<http://lists.llvm.org/pipermail/llvm-dev/2016-May/098980.html>

– Steve
> On Sep 28, 2017, at 9:31 AM, Stephen Canon via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> What code did you write where you expected VMOVNTDQ to be generated?
> 
> The x86 MOVNT instructions are something of an attractive nuisance. There
are cases where they are beneficial, but those cases are much less common and
harder to characterize than you might expect. LLVM is deliberately conservative
about using MOVNT (IIRC it’s currently only generated if you explicitly ask for
it by using intrinsics).
> 
> – Steve
> 
>> On Sep 28, 2017, at 9:10 AM, hameeza ahmed via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
>> 
>> Hello, i am using llvm 4.0 i am generating intel avx code. But in code
i dont find VMOVNTDQ instruction. Why is that so? When does this instruction
generated?
>> 
>> 
>> Please clarify.
>> _______________________________________________
>> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20170928/42cc858d/attachment.html>