Hi,
This patch rewrites classification part of builtin partition so that nested
builtin partitions are supported.  With this extension, below loop nest:
void
foo (void)
{
  for (unsigned i = 0; i < M; ++i)
    for (unsigned j = 0; j < N; ++j)
      arr[i][j] = 0;

will be distributed into a single memset, rather than a loop of memset.
Bootstrap and test in patch set on x86_64 and AArch64, is it OK?

Thanks,
bin
2017-10-04  Bin Cheng  <bin.cheng@arm.com>

	* tree-loop-distribution.c (struct builtin_info): New struct.
	(struct partition): Refactor fields into struct builtin_info.
	(partition_free): Free struct builtin_info.
	(build_size_arg_loc, build_addr_arg_loc): Delete.
	(generate_memset_builtin, generate_memcpy_builtin): Get memory range
	information from struct builtin_info.
	(find_single_drs): New function refactored from classify_partition.
	Also moved builtin validity checks to this function.
	(compute_access_range, alloc_builtin): New functions.
	(classify_builtin_1, classify_builtin_2): New functions.
	(classify_partition): Refactor code into functions find_single_drs,
	classify_builtin_1 and classify_builtin_2.
	(distribute_loop): Don't do runtime alias check when distributing
	loop nest.
	(find_seed_stmts_for_distribution): New function.
	(pass_loop_distribution::execute): Refactor code finding seed
	stmts into above function.  Support distribution for the innermost
	two-level loop nest.  Adjust dump information.

gcc/testsuite/ChangeLog
2017-10-04  Bin Cheng  <bin.cheng@arm.com>

	* gcc.dg/tree-ssa/ldist-28.c: New test.
	* gcc.dg/tree-ssa/ldist-29.c: New test.
	* gcc.dg/tree-ssa/ldist-30.c: New test.
	* gcc.dg/tree-ssa/ldist-31.c: New test.