From: Alex Riesen <raa.lkml@gmail.com>
Date: Sun, 07 Oct 2007 21:57:49 GMT
Subject: Re: [PATCH] Make strbuf_cmp inline, constify its arguments and optimize it a bit
Message-ID: <20071007215749.GD2765@steel.home>
In-Reply-To: <851wc6lwkc.fsf@lola.goethe.zz>

David Kastrup, Sun, Oct 07, 2007 18:27:15 +0200:
> Alex Riesen <raa.lkml@gmail.com> writes:
> >> > +static inline int strbuf_cmp(const struct strbuf *a, const struct strbuf *b)
> >> > +{
> >> > +	int len = a->len < b->len ? a->len: b->len;
> >> > +	int cmp = memcmp(a->buf, b->buf, len);
> >> > +	if (cmp)
> >> > +		return cmp;
> >> > +	return a->len < b->len ? -1: a->len != b->len;
> >> > +}
> >> 
> >> My guess is that you are conflating two issues about speed here: the
> >> inlining will like speed the stuff up.  But having to evaluate the
> >> (a->len < b->len) comparison twice will likely slow it down.
> >
> > Can't the result of the expression be reused in compiled?
> > Isn't it a common expression?
> 
> No, since the call to memcmp might change a->len or b->len.  A

Huh?! How's that? It is not even given them!