[patch, fortran] Two tweaks to argument repacking

[Thomas Koenig]

Hello world,

this patch adds two tweaks to the argument repacking.

First, when the size of an argument is known to be one, as in a(n1:n1),
we can directly pass a pointer - the stride may not be one, but it
does not matter.

Second, the case where the array passed is actually contiguous is
more likely in practice, so it should get the fast path. I have
done this by defining a new predictor and setting the estimated
likelyhood at 75%, which ensured a path without jumps when the
arguments passed to bar were contiguous:

module y
contains
   subroutine bar(a,b)
     real, dimension(:) :: a,b
     call foo(a,b,size(a))
   end subroutine bar
end module y

Test case is only for the first part - making one for the second
part would have been a bit too much.

Regression-tested. OK for trunk?

Regards

	Thomas

2019-06-02  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/90539
	* trans-expr.c (gfc_conv_subref_array_arg): If the size of the
	expression can be determined to be one, treat it as contiguous.
	Set likelyhood of presence of an actual argument according to
	PRED_FORTRAN_ABSENT_DUMMY and likelyhood of being contiguous
	according to PRED_FORTRAN_CONTIGUOUS.

2019-06-02  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/90539
	* predict.def (PRED_FORTRAN_CONTIGUOUS): New predictor.
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