Make SRA re-construct orginal memory accesses when easy

Make SRA re-construct orginal memory accesses when easy

2019-06-06  Martin Jambor  <mjambor@suse.cz>

	* tree-sra.c (struct access): New field grp_same_access_path.
	(dump_access): Dump it.
	(build_reconstructed_reference): New function.
	(build_ref_for_model): Use it if possible.
	(path_comparable_for_same_access): New function.
	(same_access_path_p): Likewise.
	(sort_and_splice_var_accesses): Set the new flag.
	(analyze_access_subtree): Likewise.
	(propagate_subaccesses_across_link): Propagate zero value of the new
	flag down the access tree.

	testsuite/
	* gcc.dg/tree-ssa/alias-access-path-1.c: Remove -fno-tree-sra option.
	* gcc.dg/tree-ssa/ssa-dse-26.c: Disable FRE.
	* testsuite/gnat.dg/opt39.adb: Adjust scan dump.

From-SVN: r272012