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Subject: Re: [PATCH 3/3] powerpc/bpf: Reallocate BPF registers to volatile
 registers when possible on PPC64
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To: Jordan Niethe <jniethe5@gmail.com>, linuxppc-dev@lists.ozlabs.org
References: <20210727065539.299598-1-jniethe5@gmail.com>
 <20210727065539.299598-3-jniethe5@gmail.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
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Le 27/07/2021 à 08:55, Jordan Niethe a écrit :
> Implement commit 40272035e1d0 ("powerpc/bpf: Reallocate BPF registers to
> volatile registers when possible on PPC32") for PPC64.
> 
> When the BPF routine doesn't call any function, the non volatile
> registers can be reallocated to volatile registers in order to avoid
> having to save them/restore on the stack. To keep track of which
> registers can be reallocated to make sure registers are set seen when
> used.
> 
> Before this patch, the test #359 ADD default X is:
>     0:   nop
>     4:   nop
>     8:   std     r27,-40(r1)
>     c:   std     r28,-32(r1)
>    10:   xor     r8,r8,r8
>    14:   rotlwi  r8,r8,0
>    18:   xor     r28,r28,r28
>    1c:   rotlwi  r28,r28,0
>    20:   mr      r27,r3
>    24:   li      r8,66
>    28:   add     r8,r8,r28
>    2c:   rotlwi  r8,r8,0
>    30:   ld      r27,-40(r1)
>    34:   ld      r28,-32(r1)
>    38:   mr      r3,r8
>    3c:   blr
> 
> After this patch, the same test has become:
>     0:   nop
>     4:   nop
>     8:   xor     r8,r8,r8
>     c:   rotlwi  r8,r8,0
>    10:   xor     r5,r5,r5
>    14:   rotlwi  r5,r5,0
>    18:   mr      r4,r3
>    1c:   li      r8,66
>    20:   add     r8,r8,r5
>    24:   rotlwi  r8,r8,0
>    28:   mr      r3,r8
>    2c:   blr
> 
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>

If this series is still applicable, it needs to be rebased of Naveen's 
series https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=286000

Christophe