[Bug fortran/35681] wrong result for vector subscripted array expression in MVBITS

[dick dot hendrickson at gmail dot com]

------- Comment #11 from dick dot hendrickson at gmail dot com  2008-10-18 17:02 -------
Subject: Re:  wrong result for vector subscripted array expression in MVBITS

Also, MVBITS is a special case.  See the top of page 215 in the F95
standard.  The FROM
and TO arguments are allowed to be the same variable.  The other thing
about overlapping
variables is (2) on page 205, which is a long way from the section
header and is often
overlooked (at least I missed it once).

I'm off to help paint my granddaughter's bedroom, so I can't think
much about this.

Somewhere, along time ago, there was a smallish test program of the form
            subroutine xxx(a,b)
            b = b+1
            print *, a,b
            end
and then a ton of call statements of the forms

           a = 99
           call xxx ((a),a)
           or
           call xxx( 1*a,a)
           or
           call xxx(a+0, a)
...
which might be a good thing to invent as a way to check that you
aren't oversimplifing
actual expressions.

Dick Hendrickson


On Sat, Oct 18, 2008 at 6:36 AM, burnus at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #10 from burnus at gcc dot gnu dot org  2008-10-18 11:36 -------
> Somehow reading the bug report first before replying helps ... Ignore the crap
> I just wrote.
>
> Dick's (comment 0)
>      CALL MVBITS ((ILA1(NFV3)), 2, 4, ILA1, 3)       !fails
> is valid as the first and the fourth argument don't refer to the same variable
> - the first argument is an expression for which a temporary needs to be
> created.
>
> Ditto for FX's (comment 1)
>  call mvbits ((ILA1((/9/))), 2, 4, ILA1, 3)
>
> However, comment 7's
>  CALL copy (a((/ 2, 1 /)), a)
> is wrong as one passes twice the same variable - once as array section and once
> as whole array. There an outer ( ... ) is missing which is needed to makes this
> an expression.
>
> For a lengthy answer including where to find it in the standard, see:
>
> http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/160867d13fd90927/
>
>
> Seemingly somewhere  (x)  is simplified to x (= EXPR_VARIABLE) and thus no
> temporary is created - or something like that. For non-elemental procedures
> this was fixed in gfortran 4.3; before foo((x),x) was optimized to foo((x),x).
>
> One can probably ignore all examples after comment 1 and start with looking why
> no temporary is created for comment 1 - afterwards one needs to check comment
> 0.
>
>
> --
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35681
>
> ------- You are receiving this mail because: -------
> You reported the bug, or are watching the reporter.
>


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35681