combine: Count auto_inc properly (PR89794)

combine: Count auto_inc properly (PR89794)

The code that checks if an auto-increment from i0 or i1 is not lost is
a bit shaky.  The code to check the same for i2 is non-existent, and
cannot be implemented in a similar way at all.  So, this patch counts
all auto-increments, and makes sure we end up with the same number as
we started with.  This works because we still have a check that we
will not duplicate any.

We should do this some better way, but not while we are in stage 4.

	PR rtl-optimization/89794
	* combine.c (count_auto_inc): New function.
	(try_combine): Count how many auto_inc expressions there were in the
	original instructions.  Ensure we have the same number in the new
	instructions.  Remove the code that tried to ensure auto_inc side
	effects on i1 and i0 are not lost.

gcc/testsuite/
	PR rtl-optimization/89794
	* gcc.dg/torture/pr89794.c: New testcase.

From-SVN: r270368