llvm dev - May 2015 - [LLVMdev] [AArch64] Should we restrict to the pointer type used in ldN/stN intrinsics?

Hi,

 

The ldN like intrinsics (including all the ld1xN, ldN, ldNlane, ldNr, stN,
stNlane) can use any pointer types. The definition (in IntrinsicsAArch64.td)
of such intrinsics use 'LLVMAnyPointerType', which means we can pass any
pointer type to such intrinsics.

 

E.g. I tried following case ld2.ll:

define { <4 x i32>, <4 x i32> } @test(float* %ptr) {

  %vld2 = call { <4 x i32>, <4 x i32> }
@llvm.aarch64.neon.ld2.v4i32.p0f32(float* %ptr)

  ret { <4 x i32>, <4 x i32> } %vld2

}

declare { <4 x i32>, <4 x i32> }
@llvm.aarch64.neon.ld2.v4i32.p0f32(float*)

 

It can pass and generate ld2 with "llc -march=aarch64 < ld2.ll".

 

I just think it's strange that the pointer has no relationship with the
returned type. Currently there are IR regression test cases using different
kinds of pointers like 'xx.ld2.v4i32.p0i32',
'xx.ld2.v4i32.p0v4i32' or
'xx.ld2.v4i32.p0i8', which looks confusing. Should we modify the
definition
of such intrinsics and restrict the pointer type?

 

If you agree with me, I suggest to use a pointer type to the vector element.
Because the 'arm_neon.h' declare the ld2 intrinsic like 'int32x2x2_t
vld2_s32(int32_t const * ptr)', which also uses a pointer to the vector
element. To achieve this is easy, I have a patch to add a constraint
'PointerToVectorElt' in 'intrinsics.td'. I just wonder if such
modification
is reasonable.

 

Thanks,

-Hao

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Hi Hao,
> I just think it’s strange that the pointer has no relationship with the
> returned type. Currently there are IR regression test cases using different
> kinds of pointers like ‘xx.ld2.v4i32.p0i32’, ‘xx.ld2.v4i32.p0v4i32’ or
> ‘xx.ld2.v4i32.p0i8’, which looks confusing. Should we modify the definition
> of such intrinsics and restrict the pointer type?
I'm not sure I'd bother. We're hoping to move to a single pointer
type
throughout LLVM, and this sounds like something that would just have
to be undone when we do. On the other hand, there's not been much
actual progress there for a while, at least that I've noticed.

Is is causing actual problems that you've seen, or is it a cleanliness goal?

Cheers.

Tim.

Hi Tim,

No actual problems. It's just a cleanliness goal.
It's OK that we keep it as current status.

Thanks,
-Hao
>-----Original Message-----
>From: Tim Northover [mailto:t.p.northover at gmail.com]
>Sent: 2015年5月5日 12:12
>To: Hao Liu
>Cc: Ahmed Bougacha; LLVM Developers Mailing List
>Subject: Re: [LLVMdev][AArch64] Should we restrict to the pointer type used
in
>ldN/stN intrinsics?
>
>Hi Hao,
>
>> I just think it’s strange that the pointer has no relationship with
>> the returned type. Currently there are IR regression test cases using
>> different kinds of pointers like ‘xx.ld2.v4i32.p0i32’,
>> ‘xx.ld2.v4i32.p0v4i32’ or ‘xx.ld2.v4i32.p0i8’, which looks confusing.
>> Should we modify the definition of such intrinsics and restrict the
pointer
>type?
>
>I'm not sure I'd bother. We're hoping to move to a single
pointer type
>throughout LLVM, and this sounds like something that would just have to be
>undone when we do. On the other hand, there's not been much actual
progress
>there for a while, at least that I've noticed.
>
>Is is causing actual problems that you've seen, or is it a cleanliness
goal?
>
>Cheers.
>
>Tim.