Fix tree-nrv.c ICE for direct internal functions

Fix tree-nrv.c ICE for direct internal functions

pass_return_slot::execute has:

	      /* Ignore internal functions without direct optabs,
		 those are expanded specially and aggregate_value_p
		 on their result might result in undesirable warnings
		 with some backends.  */
	      && (!gimple_call_internal_p (stmt)
		  || direct_internal_fn_p (gimple_call_internal_fn (stmt)))
	      && aggregate_value_p (TREE_TYPE (gimple_call_lhs (stmt)),
				    gimple_call_fndecl (stmt)))

But what the comment says applies to directly-mapped internal functions
too, since they're only used if the target supports them without a
libcall.

This was triggering an ICE on the attached testcase.  The svld3 call
is folded to an IFN_LOAD_LANES, which returns an array of vectors with
VNx48QImode.  Since no such return type can exist in C, the target hook
was complaining about an unexpected use of SVE modes.  (And we want to
keep asserting for that, so that we don't accidentally define an ABI for
an unexpected corner case.)

2020-01-09  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-nrv.c (pass_return_slot::execute): Handle all internal
	functions the same way, rather than singling out those that
	aren't mapped directly to optabs.

gcc/testsuite/
	* gcc.target/aarch64/sve/acle/general/nrv_1.c: New test.

From-SVN: r280048