* alias.c (alias_invariant): New variable.
	(record_base_value): New argument INVARIANT.
	(memrefs_conflict_p): If a register has an entry in the alias_invariant
	array, try substituting that value for the register.
	* rtl.h: Declare record_base_value.
	* loop.c, unroll.c: Update callers of record_base_value.
	* alias.c (find_base_value, find_base_term): SIGN_EXTEND and
	ZERO_EXTEND do not affect base values.

From-SVN: r19408