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Re: [PATCH v2 07/11] xen/bitops: Introduce generic_hweightl() and hweightl()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 29 Aug 2024 16:10:13 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 29 Aug 2024 14:10:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29.08.2024 00:03, Andrew Cooper wrote:
> There are 6 remaining callers in Xen:
>
> * The two hweight32() calls, _domain_struct_bits() and efi_find_gop_mode(),
> are __init only.
> * The two hweight_long() calls are both in bitmap_weight().
> * The two hweight64() calls are hv_vpset_nr_banks() and x86_emulate().
>
> Only bitmap_weight() and possibly hv_vpset_nr_banks() can be considered fast
> paths, and they're all of GPR-width form.
>
> Furthermore, the differences between a generic int and generic long form is
> only an ADD and SHIFT, and only in !CONFIG_HAS_FAST_MULTIPLY builds.
>
> Therefore, it is definitely not worth having both generic implemenations.
>
> Implement generic_hweightl() based on the current generic_hweight64(),
> adjusted to be compatible with ARM32, along with standard SELF_TESTS.
>
> Implement hweightl() with usual constant-folding and arch opt-in support. PPC
> is the only architecture that devates from generic, and it simply uses the
> builtin.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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