[PATCH GCC]Fix pr60363 by adding backtraced value of phi arg along jump threading path

["bin.cheng" <bin dot cheng at arm dot com>]

Hi,
After control flow graph change made by
http://gcc.gnu.org/ml/gcc-patches/2014-02/msg01492.html, case
gcc.dg/tree-ssa/ssa-dom-thread-4.c is broken on logical_op_short_circuit
targets including cortex-m3/cortex-m0.
The regression reveals a missed opportunity in jump threading, which causes
a forward basic block doesn't get removed in cfgcleanup after jump threading
in VRP1.  Root cause is stated at the corresponding PR:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60363, please refer to it for
detailed report.

This patch fixes the issue by adding constant value instead of ssa_name as
the new phi argument.  Bootstrap and test on x86_64, also test on cortex-m3
and the regression is gone.
I think this should wait for stage1, but would like to hear some comments
now.  So does it look reasonable?


2014-03-18  Bin Cheng  <bin.cheng@arm.com>

	PR regression/60363
	* gcc/tree-ssa-threadupdate.c (get_value_locus_in_path): New.
	(copy_phi_args): New parameters.  Call get_value_locus_in_path.
	(update_destination_phis): New parameter.
	(create_edge_and_update_destination_phis): Ditto.
	(ssa_fix_duplicate_block_edges): Pass new arguments.
	(thread_single_edge): Ditto.

Attachment: pr60363-20140318.txt
Description: Text document