[llvm-dev] X86 new registers not being allocated

[Quentin Colombet via llvm-dev]

Hi Barbora,

What is important for using new registers is to have instructions that are “compatible" with them.

In a nutshell, if you don’t have any instruction that uses your new register class, then it won’t be used. Basically, it is useless to have a value living in a container you cannot address.

Cheers,
-Quentin

> On Jan 21, 2018, at 4:29 PM, Barbora Murinová via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi all,
> 
> I have a bunch of new registers set up in X86RegisterInfo.td, the important part being
> 
> def PR128 : RegisterClass<"X86", [i128],
>                            128, (sequence "POI%u", 0, 7)>;   
> 
> def VR128 : RegisterClass<"X86", [v4f32, v2f64, v16i8, v8i16, v4i32, v2i64],
>                           128, (add PR128, FR32)>;
> 
> I have an entry in X86ISelLowering.cpp:
> 
> addRegisterClass(MVT::i128, &X86::PR128RegClass); 
> 
> and in findRepresentativeClass(): 
> 
> case MVT::i128:
>     RRC =  &X86::PR128RegClass;
> 
> But even though my nodes have MVT::i128 value type, they get allocated to XMM registers. I have, of course, removed i128 from FR128. What am I missing?
> 
> Thanks,
> Barbora
> 
> -- 
> ----------------
> Barbora Murinová
> The University of Edinburgh
> SK: +421905718390
> UK: +447477833795
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