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 (struct store_operand_info): Add bit_not_p
	data member.
	(store_operand_info::store_operand_info): Initialize it to false.
	(pass_store_merging::terminate_all_aliasing_chains): Rewritten to use
	ref_maybe_used_by_stmt_p and stmt_may_clobber_ref_p on lhs of each
	store in the group, and if chain_info is non-NULL, to ignore altogether
	that chain.
	(compatible_load_p): Fail if bit_not_p does not match.
	(imm_store_chain_info::output_merged_store): Handle bit_not_p loads.
	(handled_load): Fill in bit_not_p.  Handle BIT_NOT_EXPR.
	(pass_store_merging::process_store): Adjust
	terminate_all_aliasing_chains calls to pass NULL in all current spots,
	call terminate_all_aliasing_chains newly when adding a store into
	a chain with non-NULL chain_info.

	* gcc.dg/store_merging_2.c: Expect 3 store mergings instead of 2.
	* gcc.dg/store_merging_13.c (f7, f8, f9, f10, f11, f12, f13): New
	functions.
	(main): Test also those.  Expect 13 store mergings instead of 6.
	* gcc.dg/store_merging_14.c (f7, f8, f9): New functions.
	(main): Test also those.  Expect 9 store mergings instead of 6.

From-SVN: r254536