tree-optimization/99407 - DSE with data-ref analysis

tree-optimization/99407 - DSE with data-ref analysis

The following resolves the issue that DSE cannot handle references
with variable offsets well when identifying possible uses of a store.
Instead of just relying on ref_maybe_used_by_stmt_p we use data-ref
analysis, making sure to perform that at most once per stmt.  The
new mode is only exercised by the DSE pass before loop optimization
as specified by a new pass parameter and when expensive optimizations
are enabled, so it's disabled below -O2.

	PR tree-optimization/99407
	* tree-ssa-dse.cc (dse_stmt_to_dr_map): New global.
	(dse_classify_store): Use data-ref analysis to disambiguate more uses.
	(pass_dse::use_dr_analysis_p): New pass parameter.
	(pass_dse::set_pass_param): Implement.
	(pass_dse::execute): Allocate and deallocate dse_stmt_to_dr_map.
	* passes.def: Allow DR analysis for the DSE pass before loop.

	* gcc.dg/vect/tsvc/vect-tsvc-s243.c: Remove XFAIL.