[PATCH][X86] AVX512: Add vbroadcasti*

[Adam Nemet]

Hi Elena,

On Jun 25, 2014, at 12:35 AM, Demikhovsky, Elena <elena.demikhovsky at intel.com> wrote:

> Hi Adam,
> 
> I don't think that we should mix instructions like VBROADCASTI32X4 to regular, one element, broadcast.
> 
> I suggest to write one more template specially for these 2 instructions. It may be used for inserting sub-vector, where sub-vector is loaded from memory.
> I want to say  that lowering model of these 2 instructions is different. You can leave the substitution pattern empty.

Can you please be elaborate?  In this patch I just applied my conclusions from my AVX2 broadcast work (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20140526/106526.html and the first patch in http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140526/219238.html).

To summarize, I was suggesting to use the same lowering for all broadcasts there without using LLVM intrinsics.  At least that is the plan I outlined there for VBROADCAST[IF]128 which correspond to these instructions.  The main benefit is that exposing the memory loads rather than hiding them in an intrinsic opens them up to optimizations (e.g. LICM).

The idea is to use generic nodes to implement these front-end builtins then combine them into X86VBroadcast SDNodes.  In the case of vbroadcasti4x64 this would amount to: (v8i64 (X86VBroadcast (v4i64 (load ...)))).

Do you disagree with this direction for codegen?

I can of course keep them separate for now until I have prototyped either AVX2’s vbroadcasti128 or the AVX512 counterparts.  What I want to make sure at this point that we’re on the same page moving toward more of the codegen work.

Thanks,
Adam

> -  Elena
> 
> -----Original Message-----
> From: Adam Nemet [mailto:anemet at apple.com] 
> Sent: Wednesday, June 25, 2014 00:07
> To: Demikhovsky, Elena
> Cc: llvm-commits
> Subject: [PATCH][X86] AVX512: Add vbroadcasti*
> 
> Hi Elena,
> 
> I have modified the avx512_int_broadcast_rm multiclass to fit these instructions as well.
> 
> The individual patches provide a bit more information.  Please let me know if it looks good to you.
> 
> Thanks,
> Adam
> 
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