NDEBUG-like macro

[Mark Mitchell]

Folks --

  In private email, Jeff and I have been discussing the following
  proposal:

  o Add a configuration option --enable-checking to enable additional,
    possibly costly, consistency checks in the compiler.

  o This option would cause the definition of the macro ENABLE_CHECKING
    throughout compilation of the compiler.

  o Then, we could add checks in the compiler that are only enabled
    if ENABLE_CHECKING.

  The motivation for this is the disturbingly common situation in
which I find that bugs are triggered by using, say, DECL_INITIAL on a
tree node that is not a DECL.  In general, the use of a macro that
pulls something out of a tagged union when the tag doesn't match.  It
would be nice if we could blow up when we did this wrong.
Unfortunately, checking this everywhere will be quite costly; so much
so that we should not do it when a normal user is using the compiler.
Hence the need for a compile-time option.

  Jeff said:

> I'm got no particular problem with this, though I'd like to see
> it at least mentioned on the list so that Jim, Jason, etc can
> comment. 

  So, comment away!

-- 
Mark Mitchell <mmitchell@usa.net>
http://home.earthlink.net/~mbmitchell
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