llvm dev - Jun 2019 - RFC: Interface user provided vector functions with the vectorizer.

> On Jun 24, 2019, at 10:53 AM, Tian, Xinmin <xinmin.tian at intel.com>
wrote:
> 
> To me, it is also an issue related to SIMD signature matching when the
vectorizer kicks in. Losing info from FE to BE is not good in general.
>  
Yes, we cannot loose such information. In particular, the three examples I
reported are all generating i64 in the scalar function signature:

// Type 1
typedef _Complex int S;

// Type 2 
typedef struct x{
int a;
int b;
} S;

// Type 3
typedef uint64_t S;

S foo(S a, S b) {
return ...;
}


On AArch64, the correspondent vector function signature in the three cases would
be (for 2-lane unmasked vectorization):

// Type 1:

<4 x int> vectorized_foo(<4 x int>, <4 x int>)

// Type 2:

%a = type struct {I 32, i32}

<2 x %a* > vectorized_foo(<2 x %a*> , <2 x %a*>)

// Type 3:

<2 x i64> vectorized_foo(<2 x i64>, <2 x i64)

To make sure that the vectorizer knows how to map the scalar function parameters
to the vector ones, we have to make sure that the original signature 
information is stored somewhere.

I will work on this, and provide examples.

Suggestions are welcome.

Thank you

Francesco

Thanks Francesco!

-----Original Message-----
From: Francesco Petrogalli [mailto:Francesco.Petrogalli at arm.com] 
Sent: Monday, June 24, 2019 9:06 AM
To: Tian, Xinmin <xinmin.tian at intel.com>
Cc: Doerfert, Johannes <jdoerfert at anl.gov>; Saito, Hideki
<hideki.saito at intel.com>; Simon Moll <moll at
cs.uni-saarland.de>; LLVM Development List <llvm-dev at
lists.llvm.org>; Clang Dev <cfe-dev at lists.llvm.org>; Renato Golin
<rengolin at gmail.com>; Finkel, Hal J. <hfinkel at anl.gov>; Andrea
Bocci <andrea.bocci at cern.ch>; Elovikov, Andrei <andrei.elovikov at
intel.com>; Alexey Bataev <a.bataev at hotmail.com>; nd <nd at
arm.com>; Roman Lebedev <lebedev.ri at gmail.com>; Philip Reames
<listmail at philipreames.com>; Shawn Landden <slandden at
gmail.com>
Subject: Re: RFC: Interface user provided vector functions with the vectorizer.


> On Jun 24, 2019, at 10:53 AM, Tian, Xinmin <xinmin.tian at intel.com>
wrote:
> 
> To me, it is also an issue related to SIMD signature matching when the
vectorizer kicks in. Losing info from FE to BE is not good in general.
>  
Yes, we cannot loose such information. In particular, the three examples I
reported are all generating i64 in the scalar function signature:

// Type 1
typedef _Complex int S;

// Type 2 
typedef struct x{
int a;
int b;
} S;

// Type 3
typedef uint64_t S;

S foo(S a, S b) {
return ...;
}


On AArch64, the correspondent vector function signature in the three cases would
be (for 2-lane unmasked vectorization):

// Type 1:

<4 x int> vectorized_foo(<4 x int>, <4 x int>)

// Type 2:

%a = type struct {I 32, i32}

<2 x %a* > vectorized_foo(<2 x %a*> , <2 x %a*>)

// Type 3:

<2 x i64> vectorized_foo(<2 x i64>, <2 x i64)

To make sure that the vectorizer knows how to map the scalar function parameters
to the vector ones, we have to make sure that the original signature 
information is stored somewhere.

I will work on this, and provide examples.

Suggestions are welcome.

Thank you

Francesco

I mean, the FE will create only one of the 3 vector versions matching the one we
want for a given vector length, wouldn't it? The question now is: can we
with the scalar and one vector version correctly vectorize the call. If the
answer is no, what is the minimal amount of information, in addition to the two
version, we would need?

Get Outlook for Android<https://aka.ms/ghei36>

________________________________
From: Francesco Petrogalli <Francesco.Petrogalli at arm.com>
Sent: Monday, June 24, 2019 6:06:12 PM
To: Tian, Xinmin
Cc: Doerfert, Johannes; Saito, Hideki; Simon Moll; LLVM Development List; Clang
Dev; Renato Golin; Finkel, Hal J.; Andrea Bocci; Elovikov, Andrei; Alexey
Bataev; nd; Roman Lebedev; Philip Reames; Shawn Landden
Subject: Re: RFC: Interface user provided vector functions with the vectorizer.


> On Jun 24, 2019, at 10:53 AM, Tian, Xinmin <xinmin.tian at intel.com>
wrote:
>
> To me, it is also an issue related to SIMD signature matching when the
vectorizer kicks in. Losing info from FE to BE is not good in general.
>
Yes, we cannot loose such information. In particular, the three examples I
reported are all generating i64 in the scalar function signature:

// Type 1
typedef _Complex int S;

// Type 2
typedef struct x{
int a;
int b;
} S;

// Type 3
typedef uint64_t S;

S foo(S a, S b) {
return ...;
}


On AArch64, the correspondent vector function signature in the three cases would
be (for 2-lane unmasked vectorization):

// Type 1:

<4 x int> vectorized_foo(<4 x int>, <4 x int>)

// Type 2:

%a = type struct {I 32, i32}

<2 x %a* > vectorized_foo(<2 x %a*> , <2 x %a*>)

// Type 3:

<2 x i64> vectorized_foo(<2 x i64>, <2 x i64)

To make sure that the vectorizer knows how to map the scalar function parameters
to the vector ones, we have to make sure that the original signature 
information is stored somewhere.

I will work on this, and provide examples.

Suggestions are welcome.

Thank you

Francesco
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For example, Type 2 case, scalar-foo used call by value while vector-foo used
call by ref. The question Johannes is asking is whether we can decipher that
after the fact, only by looking at the two function signatures, or need some
more info (what kind, what's minimal)? I think we need to list up cases of
interest, and for each vector ABI of interest, we need to work on the
requirements and determine whether deciphering after the fact is feasible.

I think we can make further progress on trivial cases (where FE doesn't
"change" type) while we continue working out the details on
non-trivial cases.

Thanks,
Hideki

From: Doerfert, Johannes [mailto:jdoerfert at anl.gov]
Sent: Monday, June 24, 2019 9:21 AM
To: Francesco Petrogalli <Francesco.Petrogalli at arm.com>; Tian, Xinmin
<xinmin.tian at intel.com>
Cc: Saito, Hideki <hideki.saito at intel.com>; Simon Moll <moll at
cs.uni-saarland.de>; LLVM Development List <llvm-dev at
lists.llvm.org>; Clang Dev <cfe-dev at lists.llvm.org>; Renato Golin
<rengolin at gmail.com>; Finkel, Hal J. <hfinkel at anl.gov>; Andrea
Bocci <andrea.bocci at cern.ch>; Elovikov, Andrei <andrei.elovikov at
intel.com>; Alexey Bataev <a.bataev at hotmail.com>; nd <nd at
arm.com>; Roman Lebedev <lebedev.ri at gmail.com>; Philip Reames
<listmail at philipreames.com>; Shawn Landden <slandden at
gmail.com>
Subject: Re: RFC: Interface user provided vector functions with the vectorizer.

I mean, the FE will create only one of the 3 vector versions matching the one we
want for a given vector length, wouldn't it? The question now is: can we
with the scalar and one vector version correctly vectorize the call. If the
answer is no, what is the minimal amount of information, in addition to the two
version, we would need?
Get Outlook for Android<https://aka.ms/ghei36>

________________________________
From: Francesco Petrogalli <Francesco.Petrogalli at
arm.com<mailto:Francesco.Petrogalli at arm.com>>
Sent: Monday, June 24, 2019 6:06:12 PM
To: Tian, Xinmin
Cc: Doerfert, Johannes; Saito, Hideki; Simon Moll; LLVM Development List; Clang
Dev; Renato Golin; Finkel, Hal J.; Andrea Bocci; Elovikov, Andrei; Alexey
Bataev; nd; Roman Lebedev; Philip Reames; Shawn Landden
Subject: Re: RFC: Interface user provided vector functions with the vectorizer.


> On Jun 24, 2019, at 10:53 AM, Tian, Xinmin <xinmin.tian at
intel.com<mailto:xinmin.tian at intel.com>> wrote:
>
> To me, it is also an issue related to SIMD signature matching when the
vectorizer kicks in. Losing info from FE to BE is not good in general.
>
Yes, we cannot loose such information. In particular, the three examples I
reported are all generating i64 in the scalar function signature:

// Type 1
typedef _Complex int S;

// Type 2
typedef struct x{
int a;
int b;
} S;

// Type 3
typedef uint64_t S;

S foo(S a, S b) {
return ...;
}


On AArch64, the correspondent vector function signature in the three cases would
be (for 2-lane unmasked vectorization):

// Type 1:

<4 x int> vectorized_foo(<4 x int>, <4 x int>)

// Type 2:

%a = type struct {I 32, i32}

<2 x %a* > vectorized_foo(<2 x %a*> , <2 x %a*>)

// Type 3:

<2 x i64> vectorized_foo(<2 x i64>, <2 x i64)

To make sure that the vectorizer knows how to map the scalar function parameters
to the vector ones, we have to make sure that the original signature 
information is stored somewhere.

I will work on this, and provide examples.

Suggestions are welcome.

Thank you

Francesco
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