As auto_inc_dec pass combines incs and mems from different insns, it
often causes regs to temporarily hold a value different from the one
it would before the transformation.  Debug insns within that range
would therefore end up binding to the wrong expression after the
transformation.

This patch adjusts debug binds in the affected range.

for  gcc/ChangeLog

	* auto-inc-dec.c: Include valtrack.h.  Improve comments.
	(reg_next_debug_use): New.
	(attempt_change): Propagate adjusted expression into affected
	debug insns.
	(merge_in_block): Track uses in debug insns.
	(pass_inc_dec::execute): Allocate and release
	reg_next_debug_use.

From-SVN: r265828