* function.c (frame_required_for_rtx): Remove function.
(requires_stack_frame_p): New arg set_up_by_prologue. All callers
changed. Compute a set of mentioned registers and compare against
the new arg rather than calling frame_required_for_rtx.
(thread_prologue_and_epilogue_insns): Compute the set_up_by_prologue
reg set. Convert the unconverted_simple_returns mechanism to store
jump insns rather than their basic blocks. Also check the
orig_entry_edge destination for new blocks.