fortran: Evaluate class function bounds in the scalarizer [PR121342]

fortran: Evaluate class function bounds in the scalarizer [PR121342]

There is code in gfc_conv_procedure_call that, for polymorphic
functions, initializes the scalarization array descriptor
information and forcedfully sets loop bounds.  This code is changing
the decisions made by the scalarizer behind his back, and the test shows
an example where the consequences are (badly) visible.  In the test, for
one of the actual arguments to an elemental subroutine, an offset to the
loop variable is missing to access the array, as it was the one
originally chosen to set the loop bounds from.

This could theoretically be fixed by just clearing the array of choice
for the loop bounds.  This change takes instead the harder path of
adding the missing information to the scalarizer's knowledge so that its
decision doesn't need to be forced to something else after the fact.
The array descriptor information initialisation for polymorphic
functions is moved to gfc_add_loop_ss_code (after the function call
generation), and the loop bounds initialization to a new function called
after that.

As the array chosen to set the loop bounds from is no longer forced
to be the polymorphic function result, we have to let the scalarizer set
a delta for polymorphic function results.  For regular non-polymorphic
function result arrays, they are zero-based and the temporary creation
makes the loop zero-based as well, so we can continue to skip the delta
calculation.

In the cases where a temporary is created to store the result of the
array function, the creation of the temporary shifts the loop bounds
to be zero-based.  As there was no delta for polymorphic result arrays,
the function result descriptor offset was set to zero in that case for
a zero-based array reference to be correct.  Now that the scalarizer
sets a delta, those forced offset updates have to go because they can
make the descriptor invalid and cause erroneous array references.

	PR fortran/121342

gcc/fortran/ChangeLog:

	* trans-expr.cc (gfc_conv_subref_array_arg): Remove offset
	update.
	(gfc_conv_procedure_call): For polymorphic functions, move the
	scalarizer descriptor information...
	* trans-array.cc (gfc_add_loop_ss_code): ... here, and evaluate
	the bounds to fresh variables.
	(get_class_info_from_ss): Remove offset update.
	(gfc_conv_ss_startstride): Don't set a zero value for function
	result upper bounds.
	(late_set_loop_bounds): New.
	(gfc_conv_loop_setup): If the bounds of a function result have
	been set, and no other array provided loop bounds for a
	dimension, use the function result bounds as loop bounds for
	that dimension.
	(gfc_set_delta): Don't skip delta setting for polymorphic
	function results.

gcc/testsuite/ChangeLog:

	* gfortran.dg/class_elemental_1.f90: New test.