Re: [PATCH] crypto: x86/curve25519 - Remove unused carry variables

[Karthik Bhargavan <karthikeyan.bhargavan@inria.fr>]

Reviewed-by: Karthikeyan Bhargavan <karthik.bhargavan@gmail.com>

> On 27 Jul 2020, at 17:08, Karthik Bhargavan <karthikeyan.bhargavan@inria.fr> wrote:
> 
> Removing unused variables is harmless. (GCC would do this automaticelly.)
> So this change seems fine.
> 
> -Karthik
> 
>> On 23 Jul 2020, at 12:05, Jason A. Donenfeld <jason@zx2c4.com> wrote:
>> 
>> Hi Herbert,
>> 
>> On Thu, Jul 23, 2020 at 9:51 AM Herbert Xu <herbert@gondor.apana.org.au> wrote:
>>> 
>>> The carry variables are assigned but never used, which upsets
>>> the compiler.  This patch removes them.
>>> 
>>> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
>>> 
>>> diff --git a/arch/x86/crypto/curve25519-x86_64.c b/arch/x86/crypto/curve25519-x86_64.c
>>> index 8a17621f7d3a..8acbb6584a37 100644
>>> --- a/arch/x86/crypto/curve25519-x86_64.c
>>> +++ b/arch/x86/crypto/curve25519-x86_64.c
>>> @@ -948,10 +948,8 @@ static void store_felem(u64 *b, u64 *f)
>>> {
>>>       u64 f30 = f[3U];
>>>       u64 top_bit0 = f30 >> (u32)63U;
>>> -       u64 carry0;
>>>       u64 f31;
>>>       u64 top_bit;
>>> -       u64 carry;
>>>       u64 f0;
>>>       u64 f1;
>>>       u64 f2;
>>> @@ -970,11 +968,11 @@ static void store_felem(u64 *b, u64 *f)
>>>       u64 o2;
>>>       u64 o3;
>>>       f[3U] = f30 & (u64)0x7fffffffffffffffU;
>>> -       carry0 = add_scalar(f, f, (u64)19U * top_bit0);
>>> +       add_scalar(f, f, (u64)19U * top_bit0);
>>>       f31 = f[3U];
>>>       top_bit = f31 >> (u32)63U;
>>>       f[3U] = f31 & (u64)0x7fffffffffffffffU;
>>> -       carry = add_scalar(f, f, (u64)19U * top_bit);
>>> +       add_scalar(f, f, (u64)19U * top_bit);
>>>       f0 = f[0U];
>>>       f1 = f[1U];
>>>       f2 = f[2U];
>>> --
>> 
>> That seems obvious and reasonable, and so I'm inclined to ack this,
>> but I first wanted to give Karthik (CC'd) a chance to chime in here,
>> as it's his HACL* project that's responsible, and he might have some
>> curious insight.
>> 
>> Jason
>