[Bug c/26367] New: multiple levels of __builtin_expect

["acahalan at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

My expectation may be:

a. certain (OK if the code crashes when I lie)
b. strong
c. weak

This could be expressed as an optional 3rd argument to state the estimated
probability. Alternately, stuff like __builtin_expect_strongly() could be used.

I'd like to use this to inform gcc that certain bit patterns or value ranges
are impossible. The main hope is that gcc can optimize switch() better by
letting all the can't-happen cases do undefined behavior. Math should be better
too, for example not needing to worry about the sign bit (more instruction
choice, etc.) if I tell gcc that it will never be set.


-- 
           Summary: multiple levels of __builtin_expect
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: acahalan at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26367