When we are adding a single store into a store group, we are already
checking that store->lp_nr matches, but we have also code to add further
INTEGER_CST stores into the group right away if the ordering requires that
either we put there all or none from a certain set of stores.  And in those
cases we weren't doing these lp_nr checks, which means we could end up with
stores with different lp_nr in the same group, which then ICEs during
output_merged_store.

2020-03-20  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/94224
	* gimple-ssa-store-merging.c
	(imm_store_chain_info::coalesce_immediate): Don't consider overlapping
	or adjacent INTEGER_CST rhs_code stores as mergeable if they have
	different lp_nr.

	* g++.dg/tree-ssa/pr94224.C: New test.