Hardware vs software speculation mechanism

Hardware versus software speculation mechanisms speculate extensively, must be able to disambiguate memory references Much easier in HW than in SW for code with pointers HW-based speculation works better when control flow is unpredictable, and when HW-based branch prediction is superior to SW-based branch prediction done at compile time Mispredictions mean wasted speculation HW-based speculation maintains precise exception model even for speculated instructions HW-based speculation does not require compensation or bookkeeping code Compiler-based approaches may benefit from the ability to see further in the code sequence, resulting in better code scheduling HW-based speculation with dynamic scheduling does not require different code sequences to achieve good performance for different implementations of an architecture.