[Bug target/62173] [5.0 regression] [AArch64] Performance regression due to r213488

[jiwang at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62173

--- Comment #5 from Jiong Wang <jiwang at gcc dot gnu.org> ---
The root cause is AArch64's TARGET_LEGITIMIZE_ADDRESS are not doing well when
the input is ((reg + reg) + offset).

looks like currently we have considered reg + non_normal_offset, and trying to
split non_normal_offset to base + offset.

while for ((reg1 + reg2) + offset), if reg + offset is valid, then we should
legitimize it to

reg3 = reg1 + offset
return reg3 + reg2

will send out the patch after pass tests and benchmarking.