On 10/19/20 8:12 AM, Peter Maydell wrote: > v8.1M's "low-overhead-loop" extension has three instructions > for looping: > * DLS (start of a do-loop) > * WLS (start of a while-loop) > * LE (end of a loop) > > The loop-start instructions are both simple operations to start a > loop whose iteration count (if any) is in LR. The loop-end > instruction handles "decrement iteration count and jump back to loop > start"; it also caches the information about the branch back to the > start of the loop to improve performance of the branch on subsequent > iterations. > > As with the branch-future instructions, the architecture permits an > implementation to discard the LO_BRANCH_INFO cache at any time, and > QEMU takes the IMPDEF option to never set it in the first place > (equivalent to discarding it immediately), because for us a "real" > implementation would be unnecessary complexity. > > (This implementation only provides the simple looping constructs; the > vector extension MVE (Helium) adds some extra variants to handle > looping across vectors. We'll add those later when we implement > MVE.) > > Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > --- > target/arm/t32.decode | 8 ++++ > target/arm/translate.c | 93 +++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 99 insertions(+), 2 deletions(-)
Reviewed-by: Richard Henderson <richard.hender...@linaro.org> r~
