Re: [063/nnn] poly_int: vectoriser vf and uf

[Jeff Law <law@redhat.com>]

On 10/23/2017 11:26 AM, Richard Sandiford wrote:
> This patch changes the type of the vectorisation factor and SLP
> unrolling factor to poly_uint64.  This in turn required some knock-on
> changes in signedness elsewhere.
> 
> Cost decisions are generally based on estimated_poly_value,
> which for VF is wrapped up as vect_vf_for_cost.
> 
> The patch doesn't on its own enable variable-length vectorisation.
> It just makes the minimum changes necessary for the code to build
> with the new VF and UF types.  Later patches also make the
> vectoriser cope with variable TYPE_VECTOR_SUBPARTS and variable
> GET_MODE_NUNITS, at which point the code really does handle
> variable-length vectors.
> 
> The patch also changes MAX_VECTORIZATION_FACTOR to INT_MAX,
> to avoid hard-coding a particular architectural limit.
> 
> The patch includes a new test because a development version of the patch
> accidentally used file print routines instead of dump_*, which would
> fail with -fopt-info.
> 
> 
> 2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
> 	    Alan Hayward  <alan.hayward@arm.com>
> 	    David Sherwood  <david.sherwood@arm.com>
> 
> gcc/
> 	* tree-vectorizer.h (_slp_instance::unrolling_factor): Change
> 	from an unsigned int to a poly_uint64.
> 	(_loop_vec_info::slp_unrolling_factor): Likewise.
> 	(_loop_vec_info::vectorization_factor): Change from an int
> 	to a poly_uint64.
> 	(MAX_VECTORIZATION_FACTOR): Bump from 64 to INT_MAX.
> 	(vect_get_num_vectors): New function.
> 	(vect_update_max_nunits, vect_vf_for_cost): Likewise.
> 	(vect_get_num_copies): Use vect_get_num_vectors.
> 	(vect_analyze_data_ref_dependences): Change max_vf from an int *
> 	to an unsigned int *.
> 	(vect_analyze_data_refs): Change min_vf from an int * to a
> 	poly_uint64 *.
> 	(vect_transform_slp_perm_load): Take the vf as a poly_uint64 rather
> 	than an unsigned HOST_WIDE_INT.
> 	* tree-vect-data-refs.c (vect_analyze_possibly_independent_ddr)
> 	(vect_analyze_data_ref_dependence): Change max_vf from an int *
> 	to an unsigned int *.
> 	(vect_analyze_data_ref_dependences): Likewise.
> 	(vect_compute_data_ref_alignment): Handle polynomial vf.
> 	(vect_enhance_data_refs_alignment): Likewise.
> 	(vect_prune_runtime_alias_test_list): Likewise.
> 	(vect_shift_permute_load_chain): Likewise.
> 	(vect_supportable_dr_alignment): Likewise.
> 	(dependence_distance_ge_vf): Take the vectorization factor as a
> 	poly_uint64 rather than an unsigned HOST_WIDE_INT.
> 	(vect_analyze_data_refs): Change min_vf from an int * to a
> 	poly_uint64 *.
> 	* tree-vect-loop-manip.c (vect_gen_scalar_loop_niters): Take
> 	vfm1 as a poly_uint64 rather than an int.  Make the same change
> 	for the returned bound_scalar.
> 	(vect_gen_vector_loop_niters): Handle polynomial vf.
> 	(vect_do_peeling): Likewise.  Update call to
> 	vect_gen_scalar_loop_niters and handle polynomial bound_scalars.
> 	(vect_gen_vector_loop_niters_mult_vf): Assert that the vf must
> 	be constant.
> 	* tree-vect-loop.c (vect_determine_vectorization_factor)
> 	(vect_update_vf_for_slp, vect_analyze_loop_2): Handle polynomial vf.
> 	(vect_get_known_peeling_cost): Likewise.
> 	(vect_estimate_min_profitable_iters, vectorizable_reduction): Likewise.
> 	(vect_worthwhile_without_simd_p, vectorizable_induction): Likewise.
> 	(vect_transform_loop): Likewise.  Use the lowest possible VF when
> 	updating the upper bounds of the loop.
> 	(vect_min_worthwhile_factor): Make static.  Return an unsigned int
> 	rather than an int.
> 	* tree-vect-slp.c (vect_attempt_slp_rearrange_stmts): Cope with
> 	polynomial unroll factors.
> 	(vect_analyze_slp_cost_1, vect_analyze_slp_instance): Likewise.
> 	(vect_make_slp_decision): Likewise.
> 	(vect_supported_load_permutation_p): Likewise, and polynomial
> 	vf too.
> 	(vect_analyze_slp_cost): Handle polynomial vf.
> 	(vect_slp_analyze_node_operations): Likewise.
> 	(vect_slp_analyze_bb_1): Likewise.
> 	(vect_transform_slp_perm_load): Take the vf as a poly_uint64 rather
> 	than an unsigned HOST_WIDE_INT.
> 	* tree-vect-stmts.c (vectorizable_simd_clone_call, vectorizable_store)
> 	(vectorizable_load): Handle polynomial vf.
> 	* tree-vectorizer.c (simduid_to_vf::vf): Change from an int to
> 	a poly_uint64.
> 	(adjust_simduid_builtins, shrink_simd_arrays): Update accordingly.
> 
> gcc/testsuite/
> 	* gcc.dg/vect-opt-info-1.c: New test.
> 

OK.

Phew.  These are getting bigger...

As I go through this I find myself wondering if as a project we would be
better off moving to a different review model.  A whole lot of this
stuff is pretty straightforward once the basic design is agreed upon --
at which point review isn't adding much.

So I find myself wondering if we ought to (in the future for large work
like this) agree on the overall design, then let the implementer run
with the mechanical stuff and explicitly ask for acks on specific things
that depart from the mechanical changes.   It'd really help something
like this work move forward -- similarly if we want to do something like
introducing wrapping classes like I recently did with all the VRP stuff.


Anyway, as a long term contributor I'd be interested in hearing your
thoughts.

jeff