re PR target/84272 (AddressSanitizer: heap-use-after-free ../../gcc/config/aarch64/cortex-a57-fma-steering.c:519 in fma_node::get_parity())

	PR target/84272
	* config/aarch64/cortex-a57-fma-steering.c (fma_forest::merge_forest):
	Use ++iter rather than iter++ for std::list iterators.
	(func_fma_steering::dfs): Likewise.  Don't delete nodes right away,
	defer deleting them until all nodes in the forest are processed.  Do
	free even leaf nodes.  Change to_process into auto_vec.

	* g++.dg/opt/pr84272.C: New test.

From-SVN: r257727