4.5 Branch Prediction

Following the VLIW philosophy of enabling the software to communicate its needs to the hardware, branch instructions in Defoe can advise the processor about their expected behavior. A two bit hint associated with every branch may be interpreted as shown in Table 1.

Table 1: Branch Prediction Hints

Opcode Modifier	Meaning
Stk	Static prediction. Branch is usually taken.
Sntk	Static prediction. Branch is usually not taken.
Dtk	Dynamic prediction. Assume branch is taken if no history is available.
Dntk	Dynamic prediction. Assume branch is not taken if no history is available.

Implementations of the Defoe architecture may provide branch prediction hardware, but a branch predictor is not required in a minimal implementation. If branch prediction hardware is provided, static branches need not be entered in the branch history table, thereby freeing up resources for dynamically predicted branches.