rs6000: Don't emit a use of LR in returns and sibcalls

rs6000: Don't emit a use of LR in returns and sibcalls

The exit block (to which every return artificially jumps) already has
a use of LR.  The LR use in all returns and sibcalls is an anachronism,
probably made unnecessary by the dataflow merge.  The simple_returns
that shrink-wrapping generates also do not have such a use.  Newer
backends do not do this either it seems.

With this use removed, a normal return is no longer a parallel but just
a return insn, and cfgcleanup then can transform conditional jumps to
those into conditional returns.

This splits the return emission code with restoring_FPRs_inline from
that without it; this is simpler code, fewer lines, and less indentation.

The return_internal_<mode> pattern can now be deleted since nothing uses
it anymore.

	* config/rs6000/rs6000.c (rs6000_emit_epilogue): Do not emit
	USEs of LR_REGNO in returns and sibcalls.
	(rs6000_output_mi_thunk): Similar.
	(rs6000_sibcall_aix): Similar.
	* config/rs6000/rs6000.md (sibcall, sibcall_value, sibcall_local32,
	sibcall_local64, sibcall_value_local32, sibcall_value_local64,
	sibcall_nonlocal_sysv<mode>, sibcall_value_nonlocal_sysv<mode>):
	Remove the USE of LR_REGNO from the patterns as well.  Delete an
	obsolete comment.
	(return_internal_<mode>): Delete.

From-SVN: r239866