re PR tree-optimization/52171 (memcmp/strcmp/strncmp can be optimized when the result is tested for [in]equality with 0)

        PR tree-optimization/52171
        * builtins.c (expand_cmpstrn_or_cmpmem): Delete, moved elsewhere.
        (expand_builtin_memcmp): New arg RESULT_EQ.  All callers changed.
        Look for constant strings.  Move some code to emit_block_cmp_hints
        and use it.
        * builtins.def (BUILT_IN_MEMCMP_EQ): New.
        * defaults.h (COMPARE_MAX_PIECES): New macro.
        * expr.c (move_by_pieces_d, store_by_pieces_d): Remove old structs.
        (move_by_pieces_1, store_by_pieces_1, store_by_pieces_2): Remvoe.
        (clear_by_pieces_1): Don't declare.  Move definition before use.
        (can_do_by_pieces): New static function.
        (can_move_by_pieces): Use it.  Return bool.
        (by_pieces_ninsns): Renamed from move_by_pieces_ninsns.  New arg
        OP.  All callers changed.  Handle COMPARE_BY_PIECES.
        (class pieces_addr); New.
        (pieces_addr::pieces_addr, pieces_addr::decide_autoinc,
        pieces_addr::adjust, pieces_addr::increment_address,
        pieces_addr::maybe_predec, pieces_addr::maybe_postinc): New member
        functions for it.
        (class op_by_pieces_d): New.
        (op_by_pieces_d::op_by_pieces_d, op_by_pieces_d::run): New member
        functions for it.
        (class move_by_pieces_d, class compare_by_pieces_d,
        class store_by_pieces_d): New subclasses of op_by_pieces_d.
        (move_by_pieces_d::prepare_mode, move_by_pieces_d::generate,
        move_by_pieces_d::finish_endp, store_by_pieces_d::prepare_mode,
        store_by_pieces_d::generate, store_by_pieces_d::finish_endp,
        compare_by_pieces_d::generate, compare_by_pieces_d::prepare_mode,
        compare_by_pieces_d::finish_mode): New member functions.
        (compare_by_pieces, emit_block_cmp_via_cmpmem): New static
        functions.
        (expand_cmpstrn_or_cmpmem): Moved here from builtins.c.
        (emit_block_cmp_hints): New function.
        (move_by_pieces, store_by_pieces, clear_by_pieces): Rewrite to just
        use the newly defined classes.
        * expr.h (by_pieces_constfn): New typedef.
        (can_store_by_pieces, store_by_pieces): Use it in arg declarations.
        (emit_block_cmp_hints, expand_cmpstrn_or_cmpmem): Declare.
        (move_by_pieces_ninsns): Don't declare.
        (can_move_by_pieces): Change return value to bool.
        * target.def (TARGET_USE_BY_PIECES_INFRASTRUCTURE_P): Update docs.
        (compare_by_pieces_branch_ratio): New hook.
        * target.h (enum by_pieces_operation): Add COMPARE_BY_PIECES.
        (by_pieces_ninsns): Declare.
        * targethooks.c (default_use_by_pieces_infrastructure_p): Handle
        COMPARE_BY_PIECES.
        (default_compare_by_pieces_branch_ratio): New function.
        * targhooks.h (default_compare_by_pieces_branch_ratio): Declare.
        * doc/tm.texi.in (STORE_MAX_PIECES, COMPARE_MAX_PIECES): Document.
        * doc/tm.texi: Regenerate.
        * tree-ssa-strlen.c: Include "builtins.h".
        (handle_builtin_memcmp): New static function.
        (strlen_optimize_stmt): Call it for BUILT_IN_MEMCMP.
        * tree.c (build_common_builtin_nodes): Create __builtin_memcmp_eq.

testsuite/
        PR tree-optimization/52171
        * gcc.dg/pr52171.c: New test.
        * gcc.target/i386/pr52171.c: New test.

From-SVN: r237069