[J3] Lower bound of an allocatable array function result

[Bill Long]

I tried our compiler on Jon’s test case:

> ftn test1.f90
> ./a.out
 lbound(y) =    -1 ; y =  1,  2,  3
 lbound(f()) =  -3
 lbound(z) =    1 ; z =  1,  2,  3
 lbound(f()) =  -1
 lbound(z) =    1 ; z =  1,  2,  3

Not quite the same as Daniel’s output.   The rule that seems to apply is that z is allocated  "the shape of expr with each lower bound equal to the corresponding element of LBOUND (expr) if expr is an array”.  So I guess the question is whether the function reference “is an array” for the meaning of this requirement.   

Cheers,
Bill


> On Jun 14, 2019, at 12:48 PM, Daniel C Chen via J3 <j3 at mailman.j3-fortran.org> wrote:
> 
> I got:
> 
> > a.out
> lbound(y) = -1 ; y = 1 2 3
> lbound(f()) = 1
> lbound(z) = -3 ; z = 1 2 3
> lbound(f()) = 1
> lbound(z) = -1 ; z = 1 2 3
> 
> I think 10.2.1.3 Interpretation of intrinsic assignment defines the low bound of y should be the same as the "expr".
> 
> Thanks,
> 
> Daniel
> 
> XL Fortran Development, Fortran Standard Representative
> IBM Toronto Software Lab
> Phone: 905-413-3056 
> Tie: 969-3056 
> Email: cdchen at ca.ibm.com
> http://www.ibm.com/software/awdtools/fortran/xlfortran
> 
> <graycol.gif>"Steidel, Jon L via J3" ---06/14/2019 12:28:40 PM---5.4.10 Allocatable variables p3 states: "If an allocatable variable is an array, the rank is decla
> 
> From: "Steidel, Jon L via J3" <j3 at mailman.j3-fortran.org>
> To: General J3 interest list <j3 at mailman.j3-fortran.org>
> Cc: "Steidel, Jon L" <jon.l.steidel at intel.com>, "Shu, Michael" <michael.shu at intel.com>
> Date: 06/14/2019 12:28 PM
> Subject: [EXTERNAL] [J3] Lower bound of an allocatable array function result
> Sent by: "J3" <j3-bounces at mailman.j3-fortran.org>
> 
> 
> 
> 
> 5.4.10 Allocatable variables p3 states:
> “If an allocatable variable is an array, the rank is declared, but the bounds are determined when it is allocated.”
> 
> 9.7.1.2 Execution of an ALLOCATE statement p1 states:
> “When an allocate statement is executed for an array for which <allocate-shape-spec-list> is specified, the values
> of the lower and upper bound expressions determine the bounds of the array.”
> 
> 10.2.1.3 Interpretation of intrinsic assignments p3 states:
> “If the variable is or becomes an unallocated allocatable variable, it is then allocated with
> · . . . 
> · The shape of expr with each lower bound equal to the corresponding element of LBOUND (expr) if
> expr is an array.
> 
> 15.5.3 Function reference p1 states:
> “When execution of the function is complete, the value of the function result is available for use in the expression
> that caused the function to be invoked. The characteristics of the function result are determined by the interface
> of the function.”
> 
> 15.3.3 Characteristics of function results states p1 states:
> “If a function result is an array that is not allocatable or a pointer, its shape is a characteristic.
> If a type parameter of a function result or a bound of a function result array is not a constant expression, the
> exact dependence on the entities in the expression is a characteristic.”
> 
> This all leads me to believe that if an allocatable array function result is allocated with lower bounds other than 1, and 
> the result of that function is assigned to an unallocated allocatable array, the variable in the assignment statement should
> be allocated with the same bounds that the function result variable was allocated with. 
> 
> I have access to three compilers. When I compile and execute the test below, I get the same results from two of the 
> compilers, and a segmentation fault from the third. But the results show the function result lower bound, and the lower
> bound of the allocatable array that the function result is assigned to is 1.
> 
> Are the two compilers wrong, or am I missing something about the lower bounds of the result of an array valued function?
> 
> PROGRAM main
> INTEGER :: x(-1:1) = [ 1, 2, 3 ]
> INTEGER, ALLOCATABLE :: y(:)
> INTEGER, ALLOCATABLE :: z(:)
> 
> y = x
> PRINT *, "lbound(y) = ", LBOUND(y), "; y = ", y
> PRINT *, "lbound(f()) = ", LBOUND(f1())
> z = f1()
> PRINT *, "lbound(z) = ", LBOUND(z), "; z = ", z
> DEALLOCATE (z)
> PRINT *, "lbound(f()) = ", LBOUND(f2())
> z = f2()
> PRINT *, "lbound(z) = ", LBOUND(z), "; z = ", z
> 
> CONTAINS
> FUNCTION f1() RESULT( r )
> INTEGER,DIMENSION(-3:-1) :: r
> 
> r = [1, 2, 3]
> END FUNCTION
> 
> FUNCTION f2() RESULT( r )
> INTEGER, ALLOCATABLE :: r(:)
> 
> ALLOCATE ( r(-1:1))
> r = [1, 2, 3]
> END FUNCTION
> END PROGRAM
> 
> 
> 
> 
> 
> 

Bill Long                                                                       longb at cray.com
Principal Engineer, Fortran Technical Support &   voice:  651-605-9024
Bioinformatics Software Development                      fax:  651-605-9143
Cray Inc./ 2131 Lindau Lane/  Suite 1000/  Bloomington, MN  55425