On 10/12/20 8:37 AM, Peter Maydell wrote: > v8.1M implements a new 'branch future' feature, which is a > set of instructions that request the CPU to perform a branch > "in the future", when it reaches a particular execution address. > In hardware, the expected implementation is that the information > about the branch location and destination is cached and then > acted upon when execution reaches the specified address. > However the architecture permits an implementation to discard > this cached information at any point, and so guest code must > always include a normal branch insn at the branch point as > a fallback. In particular, an implementation is specifically > permitted to treat all BF insns as NOPs (which is equivalent > to discarding the cached information immediately). > > For QEMU, implementing this caching of branch information > would be complicated and would not improve the speed of > execution at all, so we make the IMPDEF choice to implement > all BF insns as NOPs. > > Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
Reviewed-by: Richard Henderson <richard.hender...@linaro.org> r~
