re PR c++/34949 (Dead code in empty destructors.)

re PR c++/34949 (Dead code in empty destructors.)

	PR c++/34949
	PR c++/50243
	* tree-eh.c (optimize_clobbers): Only remove clobbers if bb doesn't
	contain anything but clobbers, at most one __builtin_stack_restore,
	optionally debug stmts and final resx, and if it has at least one
	incoming EH edge.  Don't check for SSA_NAME on LHS of a clobber.
	(sink_clobbers): Don't check for SSA_NAME on LHS of a clobber.
	Instead of moving clobbers with MEM_REF LHS with SSA_NAME address
	which isn't defaut definition, remove them.
	(unsplit_eh, cleanup_empty_eh): Use single_{pred,succ}_{p,edge}
	instead of EDGE_COUNT comparisons or EDGE_{PRED,SUCC}.
	* tree-ssa-ccp.c (execute_fold_all_builtins): Remove clobbers
	with MEM_REF LHS with SSA_NAME address.

	* g++.dg/opt/vt3.C: New test.
	* g++.dg/opt/vt4.C: New test.

From-SVN: r197580