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| author | Ard Biesheuvel <ard.biesheuvel@linaro.org> | 2017-02-14 21:51:02 +0000 |
|---|---|---|
| committer | Herbert Xu <herbert@gondor.apana.org.au> | 2017-03-09 18:34:17 +0800 |
| commit | 27c539aeffe2851bf9aeeeba8a58038187a05019 (patch) | |
| tree | 7b886932aea0c06725a51b0cee0ff02b6cf63a4d | |
| parent | b56f5cbc7e08ec7d31c42fc41e5247677f20b143 (diff) | |
| download | lwn-27c539aeffe2851bf9aeeeba8a58038187a05019.tar.gz lwn-27c539aeffe2851bf9aeeeba8a58038187a05019.zip | |
crypto: algapi - annotate expected branch behavior in crypto_inc()
To prevent unnecessary branching, mark the exit condition of the
primary loop as likely(), given that a carry in a 32-bit counter
occurs very rarely.
On arm64, the resulting code is emitted by GCC as
9a8: cmp w1, #0x3
9ac: add x3, x0, w1, uxtw
9b0: b.ls 9e0 <crypto_inc+0x38>
9b4: ldr w2, [x3,#-4]!
9b8: rev w2, w2
9bc: add w2, w2, #0x1
9c0: rev w4, w2
9c4: str w4, [x3]
9c8: cbz w2, 9d0 <crypto_inc+0x28>
9cc: ret
where the two remaining branch conditions (one for size < 4 and one for
the carry) are statically predicted as non-taken, resulting in optimal
execution in the vast majority of cases.
Also, replace the open coded alignment test with IS_ALIGNED().
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
| -rw-r--r-- | crypto/algapi.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/crypto/algapi.c b/crypto/algapi.c index 6b52e8f0b95f..9eed4ef9c971 100644 --- a/crypto/algapi.c +++ b/crypto/algapi.c @@ -963,11 +963,11 @@ void crypto_inc(u8 *a, unsigned int size) u32 c; if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) || - !((unsigned long)b & (__alignof__(*b) - 1))) + IS_ALIGNED((unsigned long)b, __alignof__(*b))) for (; size >= 4; size -= 4) { c = be32_to_cpu(*--b) + 1; *b = cpu_to_be32(c); - if (c) + if (likely(c)) return; } |