> On 4 Nov 2024, at 13:55, Richard Biener <richard.guent...@gmail.com> wrote:
>
> On Thu, Oct 31, 2024 at 4:30 PM Jeff Law <jeffreya...@gmail.com> wrote:
>>
>>
>>
>> On 10/27/24 10:21 AM, Kyrylo Tkachov wrote:
>>> Hi all,
>>>
>>> simplify-rtx can transform (X << C1) | (X >> C2) into ROTATE (X, C1) when
>>> C1 + C2 == mode-width. But the transformation is also valid for PLUS and
>>> XOR.
>>> Indeed GIMPLE can also do the fold. Let's teach RTL to do it too.
>>>
>>> The motivating testcase for this is in AArch64 intrinsics:
>>>
>>> uint64x2_t G2(uint64x2_t a, uint64x2_t b) {
>>> uint64x2_t c = veorq_u64(a, b);
>>> return veorq_u64(vaddq_u64(c, c), vshrq_n_u64(c, 63));
>>> }
>>>
>>> which I was hoping to fold to a single XAR (a ROTATE+XOR instruction) but
>>> GCC was failing to detect the rotate operation for two reasons:
>>> 1) The combination of the two arms of the expression is done under XOR
>>> rather
>>> than IOR that simplify-rtx currently supports.
>>> 2) The ASHIFT operation is actually a (PLUS X X) operation and thus is not
>>> detected as the LHS of the two arms we require.
>>>
>>> The patch fixes both issues. The analysis of the two arms of the rotation
>>> expression is factored out into a common helper simplify_rotate which is
>>> then used in the PLUS, XOR, IOR cases in simplify_binary_operation_1.
>>>
>>> The check-assembly testcase for this is added in the following patch because
>>> it needs some extra AArch64 backend work, but I've added self-tests in this
>>> patch to validate the transformation.
>>>
>>> Bootstrapped and tested on aarch64-none-linux-gnu.
>>> Ok for mainline?
>>> Thanks,
>>> Kyrill
>>>
>>> Signed-off-by: Kyrylo Tkachov<ktac...@nvidia.com>
>>>
>>> PR target/117048
>>> * simplify-rtx.cc (extract_ashift_operands_p): Define.
>>> (simplify_rotate_op): Likewise.
>>> (simplify_context::simplify_binary_operation_1): Use the above in
>>> the PLUS, IOR, XOR cases.
>>> (test_vector_rotate): Define.
>>> (test_vector_ops): Use the above.
>> OK
>
> This seems to have broken bootstrap on multiple targets and is causing
> the arm CI to hang, miscompiling stage2 - can
> you please revert for now?
Sorry for this, I’ve pushed a revert.
I did do a clean bootstrap on aarch64-linux this morning before pushing, but
should have looked wider.
Thanks,
Kyrill
>
> Thanks,
> Richard.
>
>> jeff
>>
