On Thu, 25 Aug 2022, Richard Sandiford wrote:
> Builds of glibc with SVE enabled have been failing since V1DI was added
> to the aarch64 port. The problem is that BB SLP starts the (hopeless)
> attempt to use variable-length modes to vectorise a single-element
> vector, and that now gets further than it did before.
>
> Initially we tried getting a vector mode with 1 + 1X DI elements
> (i.e. 1 DI per 128-bit vector chunk). We don't provide such a mode --
> it would be VNx1DI -- because it isn't a native SVE format. We then
> try just 1 DI, which previously failed but now succeeds.
>
> There are numerous ways we could fix this. Perhaps the most obvious
> would be to skip variable-length modes for BB SLP. However, I think
> that'd just be kicking the can down the road, since eventually we want
> to support BB SLP and VLA vectors using predication.
>
> However, if we do use VLA vectors for BB SLP, the vector modes
> we use should actually be variable length. We don't want to use
> variable-length vectors for some element types/group sizes and
> fixed-length vectors for others, since it would be difficult
> to handle the seams.
>
> The same principle applies during loop vectorisation. We can't
> use a mixture of variable-length and fixed-length vectors for
> the same loop because the relative unroll/vectorisation factors
> would not be constant (compile-time) multiples of each other.
>
> This patch therefore makes get_related_vectype_for_scalar_type
> check that the provided number of units is interoperable with
> the provided prevailing mode. The function is generally quite
> forgiving -- it does basic things like checking for scalarness
> itself rather than expecting callers to do them -- so the new
> check feels in keeping with that.
>
> This seems to subsume the fix for PR96974. I'm not sure it's
> worth reverting that code to an assert though, so the patch just
> drops the scan for the associated message.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
OK.
Thanks,
Richard.
> Richard
>
>
> gcc/
> * tree-vect-stmts.cc (get_related_vectype_for_scalar_type): Check
> that the requested number of units is interoperable with the requested
> prevailing mode.
>
> gcc/testsuite/
> * gcc.target/aarch64/sve/slp_15.c: New test.
> * g++.target/aarch64/sve/pr96974.C: Remove scan test.
> ---
> gcc/testsuite/g++.target/aarch64/sve/pr96974.C | 4 +---
> gcc/testsuite/gcc.target/aarch64/sve/slp_15.c | 17 +++++++++++++++++
> gcc/tree-vect-stmts.cc | 10 ++++++++++
> 3 files changed, 28 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/slp_15.c
>
> diff --git a/gcc/testsuite/g++.target/aarch64/sve/pr96974.C
> b/gcc/testsuite/g++.target/aarch64/sve/pr96974.C
> index 54000f568ab..2f6ebd6ce3d 100644
> --- a/gcc/testsuite/g++.target/aarch64/sve/pr96974.C
> +++ b/gcc/testsuite/g++.target/aarch64/sve/pr96974.C
> @@ -1,5 +1,5 @@
> /* { dg-do compile } */
> -/* { dg-options "-Ofast -march=armv8.2-a+sve -fdisable-tree-fre4
> -fdump-tree-slp-details" } */
> +/* { dg-options "-Ofast -march=armv8.2-a+sve -fdisable-tree-fre4" } */
>
> float a;
> int
> @@ -14,5 +14,3 @@ struct c {
> }
> int coeffs[10];
> } f;
> -
> -/* { dg-final { scan-tree-dump "Not vectorized: Incompatible number of
> vector subparts between" "slp1" { target lp64 } } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/slp_15.c
> b/gcc/testsuite/gcc.target/aarch64/sve/slp_15.c
> new file mode 100644
> index 00000000000..23f6d567cc5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/slp_15.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-O3" } */
> +
> +struct foo
> +{
> + void *handle;
> + void *arg;
> +};
> +
> +void
> +dlinfo_doit (struct foo *args)
> +{
> + __UINTPTR_TYPE__ **l = args->handle;
> +
> + *(__UINTPTR_TYPE__ *) args->arg = 0;
> + *(__UINTPTR_TYPE__ *) args->arg = **l;
> +}
> diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
> index c9dab217f05..7748c42c70f 100644
> --- a/gcc/tree-vect-stmts.cc
> +++ b/gcc/tree-vect-stmts.cc
> @@ -11486,6 +11486,16 @@ get_related_vectype_for_scalar_type (machine_mode
> prevailing_mode,
>
> unsigned int nbytes = GET_MODE_SIZE (inner_mode);
>
> + /* Interoperability between modes requires one to be a constant multiple
> + of the other, so that the number of vectors required for each operation
> + is a compile-time constant. */
> + if (prevailing_mode != VOIDmode
> + && !constant_multiple_p (nunits * nbytes,
> + GET_MODE_SIZE (prevailing_mode))
> + && !constant_multiple_p (GET_MODE_SIZE (prevailing_mode),
> + nunits * nbytes))
> + return NULL_TREE;
> +
> /* For vector types of elements whose mode precision doesn't
> match their types precision we use a element type of mode
> precision. The vectorization routines will have to make sure
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
