re PR tree-optimization/78821 (GCC7: Copying whole 32 bits structure field by field...

re PR tree-optimization/78821 (GCC7: Copying whole 32 bits structure field by field not optimised into copying whole 32 bits at once)

	PR tree-optimization/78821
	* gimple-ssa-store-merging.c (find_bswap_or_nop_load): Give up
	if base is TARGET_MEM_REF.  If base is not MEM_REF, set base_addr
	to the address of the base rather than the base itself.
	(find_bswap_or_nop_1): Just use pointer comparison for vuse check.
	(find_bswap_or_nop_finalize): New function.
	(find_bswap_or_nop): Use it.
	(bswap_replace): Return a tree rather than bool, change first
	argument from gimple * to gimple_stmt_iterator, allow inserting
	into an empty sequence, allow ins_stmt to be NULL - then emit
	all stmts into gsi.  Fix up MEM_REF address gimplification.
	(pass_optimize_bswap::execute): Adjust bswap_replace caller.
	(struct store_immediate_info): Add N and INS_STMT non-static
	data members.
	(store_immediate_info::store_immediate_info): Initialize them
	from newly added ctor args.
	(merged_store_group::apply_stores): Formatting fixes.  Sort by
	bitpos at the end.
	(stmts_may_clobber_ref_p): For stores call also
	refs_anti_dependent_p.
	(gather_bswap_load_refs): New function.
	(imm_store_chain_info::try_coalesce_bswap): New method.
	(imm_store_chain_info::coalesce_immediate_stores): Use it.
	(split_group): Handle LROTATE_EXPR and NOP_EXPR rhs_code specially.
	(imm_store_chain_info::output_merged_store): Fail if number of
	new estimated stmts is bigger or equal than old.  Handle LROTATE_EXPR
	and NOP_EXPR rhs_code.
	(pass_store_merging::process_store): Compute n and ins_stmt, if
	ins_stmt is non-NULL and the store rhs is otherwise invalid, use
	LROTATE_EXPR rhs_code.  Pass n and ins_stmt to store_immediate_info
	ctor.
	(pass_store_merging::execute): Calculate dominators.

	* gcc.dg/store_merging_16.c: New test.

From-SVN: r254948