[PATCH][AArch64] implement aarch64 neon load/store instructions class AdvSIMD (lselem)

[Hao Liu]

Hi Tim,

OK, look forward to your patch.

Thanks,
-Hao

-----Original Message-----
From: Tim Northover [mailto:t.p.northover at gmail.com] 
Sent: Monday, October 07, 2013 5:03 PM
To: Hao Liu
Cc: llvm-commits; cfe-commits at cs.uiuc.edu
Subject: Re: [PATCH][AArch64] implement aarch64 neon load/store instructions
class AdvSIMD (lselem)

Hi Hao,

> The problem of DTriple/QTriple is that we don't have v3i64/v6i64, we 
> can't use that 2 functions in AArch64ISelLowering.cpp. So we use 
> MVT::Untype instead. We have to do something to MVT::Untype, or the test
will fail.

Yep. I'd probably make all the other ones untyped to (DPair, QPair, ...).
They're not really valid vector types in the normal LLVM sense.

> In SelectVST(), I use MVT::Untype to generate DTriple/QTriple directly 
> as your comment.  But ld.ll will fail when it is compiling st3.
> $ ./Debug+Asserts/bin/llc -march=aarch64 -mattr=+neon < st.ll ...
> Running pass 'AArch64 Instruction Selection' on function '@test_vst3q_s8'
> Segmentation fault (core dumped)

Interesting. It's the DAG scheduler that's causing problems, rather than
actual instruction selection (it's trying to find out about
register-pressure based on type). If you pass "-enable-misched" to llc then
it gets a lot further in.

It still fails, but after types are dropped, so for a completely different
reason.

> BTW, if we make v4i64/v8i64 addRegisterClass legal by using 
> addRegClass(), there will also be some problem in CopyPhysReg.

Yes, it'll also expect to be able to add v4i64s and so on. That's not a good
option, I think.

> Do you know how to solve this, or I did something wrong?

I'm very tempted to say we should just switch AArch64 over to the MISched,
since the other one is going away soon anyway.

I'll try to run some tests this evening to make sure everything works and
then send a patch to the list suggesting it. I think Ana was in favour of
the idea anyway when it came up last year.

What do you (or anyone else) think?

Cheers.

Tim.