* doc/extend.texi: (attribute leaf): Document.
	* tree.c (local_define_builtin): Handle ECF_LEAF.
	(build_common_builtin_nodes): Set ECF_LEAF where needed.
	* tree.h (ECF_LEAF): New.
	* ipa-reference.c (propagate_bits): For leaf calls propagate ever overwrittable
	and unavailable functions.
	(ipa_init): Put all_module_statics into optimization_summary_obstack.
	(copy_global_bitmap): Do not copy all_module_statics.
	(read_write_all_from_decl): Use cgraph_node argument; handle ECF_LEAF.
	(propagate): Handle overwritable and unavailable leaf functions;
	initialize global info for overwritable and unavailable leaf functions;
	do not free all module statics.
	(ipa_reference_get_not_read_global, ipa_reference_get_not_written_global):
	leaf calls don't clobber local statics.
	* calls.c (flags_from_decl_or_type): Handle leaf.
	* tree-cfg.c (stmt_can_make_abnormal_goto): Leaf functions can't do
	abnormal gotos.

	* c-common.c (handle_leaf_attribute): New function.
	(struct attribute_spec c_common_att): Add leaf.

	* gcc.dg/tree-ssa/leaf.c: New testcase.

From-SVN: r164606