> On Monday 03 March 2008 22:38, Jan Hubicka wrote: > > Hi, > > I had to tweak the testcase a bit to not compute minimum: GCC optimizes > > this early into MIN_EXPR throwing away any profile information. If we > > get serious here we can maintain it via histogram, but I am not sure it > > is worth the effort at least until IL is sanitized and expansion cleaned > > up with tupple branch. > > > > I also had to fix bug in branch prediction ignoring __builtin_expect of > > any early inlined function and update your testcase to not use > > __buliltin_expect in predictable case. > > I guess you mean, not to use it in the _unpredictable_ case?
Sure ;) > > I hope so too. For the kernel we have some parts where > __builtin_expect is used quite a lot and noticably helps, and could > help even more if we cut down the use of cmov too. I guess on > architectures with even more predictated instructions it could be > even more useful too. Looking at kernel's __builtin_expect usage, I think we ought to do a lot better on taking the hints than we do now. In particular we should be able to derrive more from likely (test1||test2) and likely (test1&&test2) and similar cases. I will try to prepare patch for this later too. I am glad to hear that __builtin_expect does useful job for you and would be interested knowing cases where it does not. Honza > > Thanks, > Nick
