PR tree-optimization/86844
	* gimple-ssa-store-merging.c
	(imm_store_chain_info::coalesce_immediate): For overlapping stores, if
	there are any overlapping stores in between them, make sure they are
	also coalesced or we give up completely.

	* gcc.c-torture/execute/pr86844.c: New test.
	* gcc.dg/store_merging_22.c: New test.
	* gcc.dg/store_merging_23.c: New test.

Co-Authored-By: Andreas Krebbel <krebbel@linux.ibm.com>

From-SVN: r264232