https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98692
--- Comment #23 from Segher Boessenkool <segher at gcc dot gnu.org> --- savegpr/restgpr are special ABI-defined functions that do not have all the same ABI calling conventions as normal functions. They indeed write into the parent's frame (red zone, in this case). Maybe you should allow this always when a function has not established a new frame? That always has to be done with a stdu 1,...(1) insn (in 64-bit; stwu in 32-bit, but the 32-bit Linux ABI has no red zone anyway) so it probably isn't too hard to detect. Only leaf functions will not establish a new frame normally (but that can happen later in the function, esp. with shrink-wrapping). Unstacking a frame is most other things that write to r1, often addi 1,1,... and sometimes ld 1,0(1) (there probably are other cases too that I am forgetting here). Maybe you should invalidate the red zone whenever r1 is changed, instead?
