Tamar Christina <tamar.christ...@arm.com> writes:
> 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 :)
I admit it probably isn't needed to fix the bug. I just though it would
look strange if we handled the arg1 extremity for m_eq_p without also
handling it for !m_eq_p.
Thanks,
Richard
>
> 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
