PR tree-optimization/87859
* gimple-ssa-store-merging.c (struct merged_store_group): Add
only_constants and first_nonmergeable_order members.
(merged_store_group::merged_store_group): Initialize them.
(merged_store_group::do_merge): Clear only_constants member if
adding something other than INTEGER_CST store.
(imm_store_chain_info::coalesce_immediate_stores): Don't merge
stores with order >= first_nonmergeable_order. Use
merged_store->only_constants instead of always recomputing it.
Set merged_store->first_nonmergeable_order if we've skipped any
stores. Attempt to merge overlapping INTEGER_CST stores that
we would otherwise skip.
* gcc.dg/store_merging_24.c: New test.
* gcc.dg/store_merging_25.c: New test.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@265794 138bc75d-0d04-0410-961f-82ee72b054a4