Dump the list of merged alias pairs

Dump the list of merged alias pairs

This patch dumps the final (merged) list of alias pairs.  It also adds:

- WAW and RAW versions of vect-alias-check-8.c
- a "well-ordered" version of vect-alias-check-9.c (i.e. all reads
  before any writes)
- a test with mixed steps in the same alias pair

I also tweaked the test value in vect-alias-check-9.c so that the
result was less likely to be accidentally correct if the alias
isn't honoured.

2019-11-16  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-data-ref.c (dump_alias_pair): New function.
	(prune_runtime_alias_test_list): Use it to dump each merged alias pair.

gcc/testsuite/
	* gcc.dg/vect/vect-alias-check-8.c: Test for the RAW flag.
	* gcc.dg/vect/vect-alias-check-9.c: Test for the ARBITRARY flag.
	(TEST_VALUE): Use a higher value for early iterations.
	* gcc.dg/vect/vect-alias-check-14.c: New test.
	* gcc.dg/vect/vect-alias-check-15.c: Likewise.
	* gcc.dg/vect/vect-alias-check-16.c: Likewise.
	* gcc.dg/vect/vect-alias-check-17.c: Likewise.

From-SVN: r278352