[Bug tree-optimization/62173] [5.0 regression] 64bit Arch can't ivopt while 32bit Arch can

["jiwang at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

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

--- Comment #24 from Jiong Wang <jiwang at gcc dot gnu.org> ---
(In reply to amker from comment #23)

partially agree.

at least for the single use case given by Seb, I think tree ivopt should do it.
(I verified clang do ivopt correctly for the case)

for the rtl re-associate, it's a little bit painful from my experiment
experiences. as it's not always good to reassociate virtual_frame + offset, we
can only benefit if it's in loop, because the re-associate will increase
register pressure, there will be situations that more callee-saved regs used,
and finally we run into unncessary push/pop in pro/epilogue... and I haven't
found a good place where we can safely re-use existed rtl info and do the rtl
re-association as I am afraid rebuild those rtl info will cause compile time
penalty.