Re: [Patch, Fortran, OOP] PR 44962: [OOP] ICE with specification expression SIZE(<CLASS>)

[Tobias Burnus <burnus at net-b dot de>]

Janus Weil wrote:
>> Can you add a comment before the gfc_is_constant_expr to state what the
>> function is actually doing (e.g. checking for specification expressions
>> while taking additionally the given constraints into account.)
>>     
> Well, it's actually not checking for specification expressions (which
> is what gfc_specification_expr does), but it checks for constant
> expressions, which are defined in chapter 7.1.12 of F08.
>   

No, it does not. A Fortran 2008 constant expression is a Fortran 2003
initialization expression and for array bounds one does not check for
F2008 constant/F2003 initialization expressions otherwise automatic
arrays would not be possible.

Seemingly, the gfortran names are based on Fortran 95 - thus looking at
F2003/F2008 does not help if one want to know what it meant. I think we
urgently need to add in the comment a reference to the relevant sections
(and terms) of all three standards - otherwise, one gets completely
confused.

That's seems to be complicated by the problem that Fortran 95 seems
define have four terms while Fortran 2003 and Fortran 2008 define only
three terms. In particular, F95 has constant and initialization
expressions, F2003 has initialization expressions, and F2008 has
constant expressions. I think I will print out the few pages of the
three standard and try to get an idea how the terms relate in the
different standards.


Fortran 95 has:

* [7.1.6.1] A *constant expression* is an expression in which each
operation is intrinsic and each primary is [...]

* [7.1.6.1] An *initialization expression* is a constant expression in
which the exponentiation operation is
permitted only with an integer power, and each primary is [...]

* [7.1.6.2] A *specification expression* is an expression with
limitations that make it suitable for use in
specifications such as character lengths (R510) and array bounds (R515,
R516). A constant
specification expression is a specification expression that is also a
constant expression.

* [7.1.6.2] A *restricted expression* is an expression in which each
operation is intrinsic and each primary is [...]


Fortran 2003 has:

* [7.1.6] A *specification expression* is an expression with limitations
that make it suitable for use in specifications such as length type
parameters (C501) and array bounds (R512, R513). [....]

* [7.1.6] A *restricted expression* is an expression in which each
operation is intrinsic and each primary is [...]

* [7.1.7] An *initialization expression* is an expression with
limitations that make it suitable for use as a kind type parameter,
initializer, or named constant. It is an expression in which each
operation is intrinsic, and each primary is [...]


Fortran 2008 has:

* [7.1.11] A *specification expression* is an expression with
limitations that make it suitable for use in specifications such as
length type parameters (C404) and array bounds (R517, R518). A
specification-expr shall be a constant expression unless it is in an
interface body (12.4.3.2), the specification part of a subprogram or
BLOCK construct, a derived-type definition, or the declaration-type-spec
of a FUNCTION statement (12.6.2.2). [...]

* [7.1.11] A *restricted expression* is an expression in which each
operation is intrinsic or dened by a specification function and each
primary is [...]

* [7.1.12] A *constant expression* is an expression with limitations
that make it suitable for use as a kind type parameter, initializer, or
named constant. It is an expression in which each operation is
intrinsic, and each primary is [...]


And gfortran has:

* gfc_is_constant_expr: Function to determine if an expression is
constant or not.  This function expects that the expression has already
been simplified.

* check_restricted: Verify that an expression is a restricted
expression.  Like its cousin check_init_expr(), an error message is
generated if we return FAILURE.

* check_init_expr: Verify that an expression is an initialization
expression. [...]

* gfc_specification_expr: Check to see that an expression is a
specification expression. If we return FAILURE, an error has been generated.


Tobias