[PATCH PR82163]Rewrite loop into lcssa form instantly

[Bin Cheng <Bin dot Cheng at arm dot com>]

Hi,
Current pcom implementation rewrites into lcssa form after all loops are transformed, this is
not enough because unrolling of later loop checks lcssa form in function tree_transform_and_unroll_loop.
This simple patch rewrites loop into lcssa form if store-store chain is handled.  I think it doesn't
affect compilation time since rewrite_into_loop_closed_ssa_1 is only called for store-store chain
transformation and only the transformed loop is rewritten.
Bootstrap and test ongoing on x86_64.  is it OK if no failures?

Thanks,
bin
2017-09-14  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/82163
	* tree-predcom.c (tree_predictive_commoning_loop): Rewrite into
	loop closed ssa instantly.  Return boolean true if loop is unrolled.
	(tree_predictive_commoning): Return TODO_cleanup_cfg if loop is
	unrolled.

gcc/testsuite
2017-09-14  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/82163
	* gcc.dg/tree-ssa/pr82163.c: New test.

Attachment: pr82163-20170914.txt
Description: pr82163-20170914.txt