jdb@mordor.s1.gov (John Bruner) (05/13/87)
> Has anyone bothered to think about adding branch instructions that tell > the CPU explicitly whether or not they expect to be taken? For example, > Compilers would be able to pick the instructions they wanted. The S-1 AAP (a research machine under construction here at LLNL) provides three flavors of branch instructions. The pipeline is four stages long -- the icache is read in the first stage and branch decisions are made during the second stage. The instruction following the branch is always fetched and can be executed always, only if the branch is not taken, or only if the branch is taken (depending upon the opcode of the branch instruction). (The hardware can support branches which never execute the instruction following a conditional branch, but that flavor of branch isn't very useful.:-) -- John Bruner (S-1 Project, Lawrence Livermore National Laboratory) jdb@mordor.s1.gov ...!seismo!mordor!jdb (415) 423-4848