Method and apparatus for predicting conditional branch instruction outcome based on branch condition test type

摘要

An apparatus and method for improving the execution of conditional branch instructions is provided. A static branch predictor makes predictions about the outcomes of branch instructions based upon a combination of the test type (such as jump on overflow, jump if negative, jump if zero, jump on carry, etc.) and the sign of the displacement of the branch instruction. If the test type of the branch instruction is one of a subset of test types from which the branch outcome can accurately be predicted solely from the test type, then the predictor makes such a prediction. Otherwise, the predictor makes a prediction based upon the sign of the displacement used to calculate the branch target address. In this case, backward jumps are predicted taken and forward jumps are predicted not taken.