tree-sra: Avoid returns of references to SRA candidates

tree-sra: Avoid returns of references to SRA candidates

The enhancement to address PR 109849 contained an importsnt thinko,
and that any reference that is passed to a function and does not
escape, must also not happen to be aliased by the return value of the
function.  This has quickly transpired as bugs PR 112711 and PR
112721.

Just as IPA-modref does a good enough job to allow us to rely on the
escaped set of variables, it sems to be doing well also on updating
EAF_NOT_RETURNED_DIRECTLY call argument flag which happens to address
exactly the situation we need to avoid.  Of course, if a call
statement ignores any returned value, we also do not need to check the
flag.

Hopefully this does not pessimize things too much, I have verified
that the PR 109849 testcae remains quick and so should also the
benchmark it is derived from.

gcc/ChangeLog:

2023-11-27  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/112711
	PR tree-optimization/112721
	* tree-sra.cc (build_access_from_call_arg): New parameter
	CAN_BE_RETURNED, disqualify any candidate passed by reference if it is
	true.  Adjust leading comment.
	(scan_function): Pass appropriate value to CAN_BE_RETURNED of
	build_access_from_call_arg.

gcc/testsuite/ChangeLog:

2023-11-29  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/112711
	PR tree-optimization/112721
	* g++.dg/tree-ssa/pr112711.C: New test.
	* gcc.dg/tree-ssa/pr112721.c: Likewise.