Add missing unit dependence vector in data dependence analysis

Add missing unit dependence vector in data dependence analysis

Current data dependence analysis misses unit distant vector if DRs in
DDR have the same invariant access functions.  This adds the vector as
the constant access function case.

Also fix typo in testcase.

Backport from master commit: 287552950d56be47adb6b6bf2eae2d612233eaec
and f6e1a4cd83190746b6544917f7526fa480ca5f18

2020-06-20  Bin Cheng  <bin.cheng@linux.alibaba.com>

gcc/
	PR tree-optimization/94969
	* tree-data-ref.c (constant_access_functions): Rename to...
	(invariant_access_functions): ...this.  Add parameter.  Check for
	invariant access function, rather than constant.
	(build_classic_dist_vector): Call above function.
	* tree-loop-distribution.c (pg_add_dependence_edges): Add comment.

gcc/testsuite/
	PR tree-optimization/94969
	* gcc.dg/tree-ssa/pr94969.c: New test.

2020-06-20  Jakub Jelinek  <jakub@redhat.com>

gcc/testsuite/
	PR tree-optimization/95110
	* gcc.dg/tree-ssa/pr94969.c: Swap scan-tree-dump-not arguments.