https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112431
--- Comment #3 from Kito Cheng <kito at gcc dot gnu.org> --- Share some thought from my end: we've tried at least 3 different approach on LLVM side before, and now we model that as "partial early clobber", we plan to upstream this on LLVM side but just didn't get high enough priority yet :( What means? Give some practical example to demo the idea: 1. It's normal live range without early clobber vadd x, y z # y and z is dead after this use. |---------------------| | read | y z | | write | x | |---------------------| 2. It's live range with early clobber. vadd x, y z # y and z is dead after this use, and assume x is early clobber. |---------------------| | read | x y z | | write | x | |---------------------| 3. It's live range with partial early clobber. vwadd.vv x, y, z # x is two time larger than y and z So we split x into xh and xl to represent the high part and low part, and assume high part can be overlap with others. |------------------------| | read | xl y z | | write | xh xl | |------------------------| And following case is assume high part can overlap with others: |------------------------| | read | xh y z | | write | xh xl | |------------------------| Then the register allocator should able to did the overlapping allocation naturally IF we build live range.
