Hi Richard,
> -----Original Message-----
> From: Richard Sandiford <richard.sandif...@arm.com>
> Sent: Wednesday, October 9, 2024 12:58 PM
> To: gcc-patches@gcc.gnu.org
> Cc: ktkac...@nvidia.com; Richard Earnshaw <richard.earns...@arm.com>;
> Tamar Christina <tamar.christ...@arm.com>
> Subject: [PATCH] aarch64: Fix folding of degenerate svwhilele case [PR117045]
>
> The svwhilele folder mishandled the degenerate case in which
> the second argument is the maximum integer. In that case,
> the result is all-true regardless of the first parameter:
>
> If the second scalar operand is equal to the maximum signed integer
> value then a condition which includes an equality test can never fail
> and the result will be an all-true predicate.
>
> This is because the conceptual "increment the first operand
> by 1 after each element" is done modulo the range of the operand.
> The GCC code was instead treating it as infinite precision.
> whilele_5.c even had a test for the incorrect behaviour.
>
> The easiest fix seemed to be to handle that case specially before
> doing constant folding. This also copes with variable first operands.
>
> Tested on aarch64-linux-gnu. I'll push on Friday if there are no
> comments before then. Since it's a wrong-code bug, I'd also like
> to backport to release branches.
>
> Thanks,
> Richard
>
>
> gcc/
> PR target/116999
> PR target/117045
> * config/aarch64/aarch64-sve-builtins-base.cc
> (svwhilelx_impl::fold): Check for WHILELTs of the minimum value
> and WHILELEs of the maximum value. Fold them to all-false and
> all-true respectively.
>
> gcc/testsuite/
> PR target/116999
> PR target/117045
> * gcc.target/aarch64/sve/acle/general/whilele_5.c: Fix bogus
> expected result.
> * gcc.target/aarch64/sve/acle/general/whilele_11.c: New test.
> * gcc.target/aarch64/sve/acle/general/whilele_12.c: Likewise.
> ---
> .../aarch64/aarch64-sve-builtins-base.cc | 11 +++++-
> .../aarch64/sve/acle/general/whilele_11.c | 31 +++++++++++++++++
> .../aarch64/sve/acle/general/whilele_12.c | 34 +++++++++++++++++++
> .../aarch64/sve/acle/general/whilele_5.c | 2 +-
> 4 files changed, 76 insertions(+), 2 deletions(-)
> create mode 100644
> gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_11.c
> create mode 100644
> gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_12.c
>
> diff --git a/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> b/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> index 4b33585d981..3d0975e4294 100644
> --- a/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> +++ b/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> @@ -2945,7 +2945,9 @@ public:
> : while_comparison (unspec_for_sint, unspec_for_uint), m_eq_p (eq_p)
> {}
>
> - /* Try to fold a call by treating its arguments as constants of type T. */
> + /* Try to fold a call by treating its arguments as constants of type T.
> + We have already filtered out the degenerate cases of X .LT. MIN
> + and X .LE. MAX. */
> template<typename T>
> gimple *
> fold_type (gimple_folder &f) const
> @@ -3001,6 +3003,13 @@ public:
> if (f.vectors_per_tuple () > 1)
> return nullptr;
>
> + /* Filter out cases where the condition is always true or always false.
> */
> + tree arg1 = gimple_call_arg (f.call, 1);
> + if (!m_eq_p && operand_equal_p (arg1, TYPE_MIN_VALUE (TREE_TYPE
> (arg1))))
> + return f.fold_to_pfalse ();
Just a quick question for my own understanding, I assume the reason MIN
is handled here is because fold_type will decrement the value at some point?
Otherwise wouldn't MIN + 1 still fit inside the type's precision?
FWIW patch looks good to me, just wondering why the MIN case is needed :)
Cheers,
Tamar
> + if (m_eq_p && operand_equal_p (arg1, TYPE_MAX_VALUE (TREE_TYPE
> (arg1))))
> + return f.fold_to_ptrue ();
> +
> if (f.type_suffix (1).unsigned_p)
> return fold_type<poly_uint64> (f);
> else
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_11.c
> b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_11.c
> new file mode 100644
> index 00000000000..2be9dc5c534
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_11.c
> @@ -0,0 +1,31 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +#include <arm_sve.h>
> +#include <limits.h>
> +
> +svbool_t
> +f1 (volatile int32_t *ptr)
> +{
> + return svwhilelt_b8_s32 (*ptr, INT32_MIN);
> +}
> +
> +svbool_t
> +f2 (volatile uint32_t *ptr)
> +{
> + return svwhilelt_b16_u32 (*ptr, 0);
> +}
> +
> +svbool_t
> +f3 (volatile int64_t *ptr)
> +{
> + return svwhilelt_b32_s64 (*ptr, INT64_MIN);
> +}
> +
> +svbool_t
> +f4 (volatile uint64_t *ptr)
> +{
> + return svwhilelt_b64_u64 (*ptr, 0);
> +}
> +
> +/* { dg-final { scan-assembler-times {\tpfalse\tp[0-9]+\.b\n} 4 } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_12.c
> b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_12.c
> new file mode 100644
> index 00000000000..713065c3145
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_12.c
> @@ -0,0 +1,34 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +#include <arm_sve.h>
> +#include <limits.h>
> +
> +svbool_t
> +f1 (volatile int32_t *ptr)
> +{
> + return svwhilele_b8_s32 (*ptr, INT32_MAX);
> +}
> +
> +svbool_t
> +f2 (volatile uint32_t *ptr)
> +{
> + return svwhilele_b16_u32 (*ptr, UINT32_MAX);
> +}
> +
> +svbool_t
> +f3 (volatile int64_t *ptr)
> +{
> + return svwhilele_b32_s64 (*ptr, INT64_MAX);
> +}
> +
> +svbool_t
> +f4 (volatile uint64_t *ptr)
> +{
> + return svwhilele_b64_u64 (*ptr, UINT64_MAX);
> +}
> +
> +/* { dg-final { scan-assembler {\tptrue\tp[0-9]+\.b(?:, all)\n} } } */
> +/* { dg-final { scan-assembler {\tptrue\tp[0-9]+\.h(?:, all)\n} } } */
> +/* { dg-final { scan-assembler {\tptrue\tp[0-9]+\.s(?:, all)\n} } } */
> +/* { dg-final { scan-assembler {\tptrue\tp[0-9]+\.d(?:, all)\n} } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_5.c
> b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_5.c
> index 7c73aa5926b..79f0e64b2ae 100644
> --- a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_5.c
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/whilele_5.c
> @@ -28,7 +28,7 @@ test3 (svbool_t *ptr)
> *ptr = svwhilele_b16_s32 (0x7ffffffb, 0x7fffffff);
> }
>
> -/* { dg-final { scan-assembler {\tptrue\tp[0-9]+\.h, vl5\n} } } */
> +/* { dg-final { scan-assembler {\tptrue\tp[0-9]+\.h(?:, all)\n} } } */
>
> void
> test4 (svbool_t *ptr)
> --
> 2.25.1
