tree-optimization/65206 - dependence analysis on mixed pointer/array

tree-optimization/65206 - dependence analysis on mixed pointer/array

This adds the capability to analyze the dependence of mixed
pointer/array accesses.  The example is from where using a masked
load/store creates the pointer-based access when an otherwise
unconditional access is array based.  Other examples would include
accesses to an array mixed with accesses from inlined helpers
that work on pointers.

The idea is quite simple and old - analyze the data-ref indices
as if the reference was pointer-based.  The following change does
this by changing dr_analyze_indices to work on the indices
sub-structure and storing an alternate indices substructure in
each data reference.  That alternate set of indices is analyzed
lazily by initialize_data_dependence_relation when it fails to
match-up the main set of indices of two data references.
initialize_data_dependence_relation is refactored into a head
and a tail worker and changed to work on one of the indices
structures and thus away from using DR_* access macros which
continue to reference the main indices substructure.

There are quite some vectorization and loop distribution opportunities
unleashed in SPEC CPU 2017, notably 520.omnetpp_r, 548.exchange2_r,
510.parest_r, 511.povray_r, 521.wrf_r, 526.blender_r, 527.cam4_r and
544.nab_r see amendments in what they report with -fopt-info-loop while
the rest of the specrate set sees no changes there.  Measuring runtime
for the set where changes were reported reveals nothing off-noise
besides 511.povray_r which seems to regress slightly for me
(on a Zen2 machine with -Ofast -march=native).

2021-09-08  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/65206
	* tree-data-ref.h (struct data_reference): Add alt_indices,
	order it last.
	* tree-data-ref.c (free_data_ref): Release alt_indices.
	(dr_analyze_indices): Work on struct indices and get DR_REF as tree.
	(create_data_ref): Adjust.
	(initialize_data_dependence_relation): Split into head
	and tail.  When the base objects fail to match up try
	again with pointer-based analysis of indices.
	* tree-vectorizer.c (vec_info_shared::check_datarefs): Do
	not compare the lazily computed alternate set of indices.

	* gcc.dg/torture/20210916.c: New testcase.
	* gcc.dg/vect/pr65206.c: Likewise.