https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64952
Bug ID: 64952
Summary: Missing temporary in assignment from elemental
function
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: pault at gcc dot gnu.org
See https://groups.google.com/forum/#!topic/comp.lang.fortran/TvVY5j3GPmg
gfortran produces wrong result from:
PROGRAM Main
INTEGER :: i, index(5) = (/ (i, i = 1,5) /)
REAL :: array(5) = (/ (i+0.0, i = 1,5) /)
array = Fred(index,array)
PRINT *, array
CONTAINS
ELEMENTAL FUNCTION Fred (n, x)
REAL :: Fred
INTEGER, INTENT(IN) :: n
REAL, INTENT(IN) :: x
! In general, this would be in an external procedure
Fred = x+SUM(array(:n-1))+SUM(array(n+1:))
END FUNCTION Fred
END PROGRAM Main
outputs
15.0000000 29.0000000 56.0000000 109.000000 214.000000
when result should be
5*15.0
A temporary should be produced for array = Fred(index, array). See the clf
thread for the reasoning.
In a nutshell, the reason that won the day (I had another point of view) is:
The execution of the assignment shall have the same effect as
if the evaluation of expr and the evaluation of all expressions
in variable occurred before any portion of the variable is
defined by the assignment. The evaluation of expressions within
variable shall neither affect nor be affected by the evaluation
of expr.
Clearly, the above code violates this requirement because of the references to
'array' in 'Fred'. I think that we will have to provide an attribute that marks
up array valued elemental functions that have any external array references and
provide a temporary for assignment from one of these. Fortunately, it only
affects contained functions so that we do not have to carry it across when
using modules.
Paul
