Static branch prediction

In MMIX, the programmer (or compiler) can tell the processor his personal prediction of the branch outcome by choosing between two variants of branch instructions:

• The Bxx instructions assume the branch is not taken; there is a penalty of two clock cycles if it is taken.
• The PBx instructions assume the branch is taken; there is a penalty of two clock cycles if it is not taken.

In processors that don't have this kind of branch hints (like all x86 processors), static branch prediction can still be hardwired into the processor based on criteria like:

• is it a forward or a backward branch?
• which flag is being tested?
• which instruction set the flag being tested?
• etc.