This patch fixes a loophole in the -fstack-protector-strong protection.
If a function call uses a return slot, the caller needs stack protector
instrumentation because the return slot is addressable. 

gcc/

2014-05-09  Florian Weimer  <fweimer@redhat.com>

	* cfgexpand.c (stack_protect_decl_p): New function, extracted from
	expand_used_vars.
	(stack_protect_return_slot_p): New function.
	(expand_used_vars): Call stack_protect_decl_p and
	stack_protect_return_slot_p for -fstack-protector-strong.

gcc/testsuite/

2014-05-09  Florian Weimer  <fweimer@redhat.com>

	* gcc.dg/fstack-protector-strong.c: Add coverage for return slots.
	* g++.dg/fstack-protector-strong.C: Likewise.
	* gcc.target/i386/ssp-strong-reg.c: New file.

From-SVN: r210275