(j3.2006) (SC22WG5.4899) [ukfortran] Comment on a comment on the WG5 letterballot on N1947

[Keith Bierman]

Inline

On Thu, Jan 17, 2013 at 12:25 PM, Craig Dedo <craig at ctdedo.com> wrote:

>
>
>
>         Although I do not have any expertise in hardware architecture or
> compiler design,
> I have reason to believe that providing for detection of integer overflow
> does not
> necessarily need to be difficult or expensive.  Apparently, this kind of
> work has already
> been done in several other contexts.
>
>         1.  The OpenVMS operating system provides for detection of many
> different kinds of
>

OpenVMS, as far as I know, has only run on processors which physical
support for overflow detection (Alpha, VAX). So this is not a very useful
proof point for the significant number of processors that do not have such
hardware support.

        2.  Detection of integer overflow conditions was part of John
> Reid's ENABLE block
> proposal in 1994.


John was proposing a language feature; he didn't have the burden of
actually implementing it, so again this example proves nothing germane to
Bill's objections.

Look at current GPU architecture manuals and hardware specifications for
examples of compute engines for which such handling could prove quite
costly (indeed, making moving computation off the CPU possibly pointless).
GPUs are similar (in many ways) to the old FPS style array processors and
Cray style vector machines (just not nearly as polished or easy to
program).

I'm not saying that these aren't useful or interesting language features.
But those without any "skin the game" w.r.t. implementing either the
hardware or software should not blithely ignore the costs proposed.
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