Messages in this thread | | | Date | Sun, 17 Feb 2008 11:08:55 +0100 | From | Willy Tarreau <> | Subject | Re: [Cbe-oss-dev] [PATCH 1/3] Fix Unlikely(x) == y |
| |
On Sun, Feb 17, 2008 at 01:45:23AM -0800, Andrew Pinski wrote: > On Feb 16, 2008 9:58 AM, Willy Tarreau <w@1wt.eu> wrote: > > Last but not least, gcc 4 tends to emit stupid checks, to the point that I > > have replaced unlikely(x) with (x) in my code when gcc >= 4 is detected. What > > I observe is that the following code : > > > > if (unlikely(p == NULL)) ... > > > > often gets coded like this : > > > > reg1 = (p == NULL) > > if (reg1 != 0) ... > > > > ... which clobbers reg1 for nothing and performs a double test. > > This really only can happen in GCC 4.0.x and 4.1.x and cannot happen > for 4.2 or 4.3 really because of the way __builtin_expect is handled > for those two.
Happy to know that, thanks for the info Andrew!
Willy
| |