https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99092
--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> --- hmmm, see https://gcc.gnu.org/legacy-ml/gcc-patches/2014-07/msg00612.html : "When it comes to emitting the pattern, always use "prfm" -- the prfum form can be generated from the prfm mnemonic when the offset implies this is necessary." >From readin the ARM ARM, it does look like the prfm mnemonic should accept the unscaled 9bit signed value. Just like how ldr vs ldur. So the bug is in LLVM assembler I think.
