The inliner folds stmts delayed, the following arranges things so
to not fold stmts that are obviously not reachable to avoid warnings
from those code regions.

2020-02-07  Richard Biener  <rguenther@suse.de>

	PR middle-end/93519
	* tree-inline.c (fold_marked_statements): Do a PRE walk,
	skipping unreachable regions.
	(optimize_inline_calls): Skip folding stmts when we didn't
	inline.

	* gcc.dg/Wrestrict-21.c: New testcase.