(j3.2006) Locality problems not repaired at Garching

Mon Jul 17 15:07:00 EDT 2017

On Mon, 2017-07-17 at 13:12 -0400, Daniel C Chen wrote:

> If the IMPLICIT statement is not allowed in a BLOCK construct as
> Malcolm indicated, should 8.7p4 become moot as it only applies to
> IMPLICIT statement? 

Even without an IMPLICIT statement in a BLOCK construct, implicit typing
is in effect within the BLOCK construct if it's in effect in the
enclosing scoping unit.  You just can't change the implicit mapping
within a BLOCK construct.

> Then the following quoted code becomes not conforming because R is
> implicitly-declared to have rank 1 in the enclosing scope of the first
> BLOCK construct (as per 19.4), and should not be implicit-declared
> with a different rank is the same scoping unit. Although XLF 15.1.5
> prints the same as ifort and nagfor. 

Since a BLOCK construct is not a type definition, 8.7p4 says the effect
is as if R "were declared in an explicit type declaration ... in that
scope."

19.4p1 says that R is a different construct entity in each BLOCK because
it is explicitly declared (in this case in DIMENSION statements).
19.4p1 doesn't say "type is explicitly declared."  So even for a scalar
that does not appear in any declaration statements, and does not appear
in the enclosing scope, the "as if" in 8.7p4 seems to indicate it's
still a construct entity.

I certainly hope it's a construct entity because in

do concurrent ( integer :: i = 1:10 ) default ( none )
  block
    r = a(i)
  end block
end do

one cannot declare R to have local locality because it isn't the name of
a variable in the innermost executable construct or scoping unit
(C1124), and without a locality spec R cannot "appear" (C1129).

Even in

do concurrent ( integer :: i = 1:10 ) default ( none )
  block
    real :: R
    r = a(i)
  end block
end do

R cannot "appear" (C1129).

> 
> block
>  dimension R(3)
>  print '(a,i0)', 'Shape(R) = ', shape(r)
> end block
> 
> block
>  dimension R(2,2)
>  print '(a,2(1x,i0))', 'Shape(R) =', shape(r)
> end block
> 
> end
> 
> prints
> 
> Shape(R) = 3
> Shape(R) = 2 2
> 
> 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
> 
> Inactive hide details for Van Snyder ---07/14/2017 09:01:33 PM---On
> Sat, 2017-07-15 at 09:20 +0900, Malcolm Cohen wrote: > I noVan Snyder
> ---07/14/2017 09:01:33 PM---On Sat, 2017-07-15 at 09:20 +0900, Malcolm
> Cohen wrote: > I note that if BLOCK affected implicitly d
> 
> From: Van Snyder <Van.Snyder at jpl.nasa.gov>
> To: j3 at mailman.j3-fortran.org
> Date: 07/14/2017 09:01 PM
> Subject: Re: (j3.2006) Locality problems not repaired at Garching
> Sent by: j3-bounces at mailman.j3-fortran.org
> 
> 
> 
> ______________________________________________________________________
> 
> 
> 
> On Sat, 2017-07-15 at 09:20 +0900, Malcolm Cohen wrote:
> > I note that if BLOCK affected implicitly declared entities, it would
> be 
> > extremely error-prone to add to existing code, and indeed if that
> were the 
> > case BLOCK would have been an extremely bad construct.  Fortunately,
> that is 
> > not the case, BLOCK has no effect on implicitly declared entities. 
> 
> It has no effect on implicitly-declared entities in the enclosing
> scope,
> which is a good thing.
> 
> But concerning implicit declaration, 8.7p4 says "The data entity is
> treated as if it were declared in an explicit type declaration; if the
> outermost inclusive scope in which it appears is not a type
> definition,
> it is declared in that scope, otherwise it is declared in the host of
> that scope."
> 
> A BLOCK construct isn't a type definition, so read this as "The data
> entity is treated as if it were declared in an explicit type
> declaration; it is declared in the outermmost inclusive scope in which
> it appears."  If it only appears in a BLOCK construct, that is the
> outermost inclusive scopes in which it appears.
> 
> So, although IMPLICIT NONE is not allowed in BLOCK constructs,
> implicitly typed variables in them do exist and are construct entities
> of those BLOCK constructs because the effect is as they were declared
> by
> explicit type declarations in those constructs (according to 8.7p4).
> Although they have the same type and kind in each BLOCK construct,
> they
> are different in each pair of disjoint BLOCK constructs in which they
> appear.  They could have different ranks and shapes (DIMENSION
> statement
> is allowed) or they might be variables in some and named constants in
> others (PARAMETER statement is allowed).
> 
> This program
> 
> block
>  dimension R(3)
>  print '(a,i0)', 'Shape(R) = ', shape(r)
> end block
> 
> block
>  dimension R(2,2)
>  print '(a,2(1x,i0))', 'Shape(R) =', shape(r)
> end block
> 
> end
> 
> prints
> 
> Shape(R) = 3
> Shape(R) = 2 2
> 
> with ifort 16.0.2.181 and nagfor Build 6117.
> 
> Since IMPLICIT NONE is not allowed in BLOCK constructs, Erik's
> question
> is moot, but since implicitly declared variables in BLOCK constructs
> exist, one might still wonder whether we intended to prohibit
> 
> do concurrent ( integer :: i = 1:10 ) default ( none )
>  block
>    r = cos(a(i))
>  end block
> end do
> 
> with implicit typing in effect, in which R is an implicitly-declared
> construct entity of the BLOCK construct, but "appears" in the <block>
> of
> the DO CONCURRENT construct.
> 
> Similarly, we appear to have prohibited
> 
> do concurrent ( integer :: i = 1:10 ) default ( none )
>  block
>    real :: R
>  end block
> end do
> 
> in which R is an explicitly-declared construct entity of the BLOCK
> construct, but "appears" in the <block> of the DO CONCURRENT
> construct,
> and
> 
> do concurrent ( integer :: i = 1:10 ) default ( none )
>  associate ( r => a(i) )
>  end associate
> end do
> 
> in which R is a construct entity of the ASSOCIATE construct, but
> "appears" in the <block> of the DO CONCURRENT construct, and
> 
> do concurrent ( integer :: i = 1:10 ) default ( none )
>  a(i,1:3) = [ ( j, integer :: j = 1,5,2) ]
> end do
> 
> in which J is a statement entity of the array constructor, but
> "appears"
> in the <block> of the DO CONCURRENT construct.
> 
> 
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> 
> 
> 
> 

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