On Sun, Aug 14, 2022 at 12:08 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
>
> There's a cheap way to reduce the register pressure:
> seq = raw_seqcount_begin(&dentry->d_seq);
> if (dentry->d_parent != parent)
> continue;
> if (d_unhashed(dentry))
> continue;
> if (dentry->d_name.hash_len != hashlen)
> continue;
> if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
> continue;
> *seqp = seq;
> could move the last store to before dentry_cmp().
I actually tried that, it doesn't really end up helping.
Gcc does well regardless, and clang ends up really wanting to move so
much out of the dentry_cmp() loop that it runs out of registers and
always ends up doing a couple of spills.
I think it reduced the spills by one, but not enough to generate the
nice non-frame code that gcc does.
It's a bit ugly, but the code probably performs quite well - the
spills aren't in the inner loop.
Linus
