This bug is exposed by FRE refactor of r263875.  Comparing the fre
dump file shows no obvious change of the segment fault function proves
it to be a target issue.
frame_pointer_needed is set to true in reload pass setup_can_eliminate,
but regs_ever_live[31] is false, pro_and_epilogue uses it without live
check causing CPU2006 465.tonto segment fault of loading from invalid
addresses due to r31 not saved/restored.  Thus, add HARD_FRAME_POINTER_REGNUM
live check with frame_pointer_needed_indeed when generating pro_and_epilogue
instructions.

gcc/ChangeLog

2020-04-27  Xiong Hu Luo  <luoxhu@linux.ibm.com>

	PR target/91518
	* config/rs6000/rs6000-logue.c (frame_pointer_needed_indeed):
	New variable.
	(rs6000_emit_prologue_components):
	Check with frame_pointer_needed_indeed.
	(rs6000_emit_epilogue_components): Likewise.
	(rs6000_emit_prologue): Likewise.
	(rs6000_emit_epilogue): Set frame_pointer_needed_indeed.