Re: PING SC members [was RE: RFA: GCC 4.2.1: Stabalizing coalesce_list's qsort]

[Geoffrey Keating <geoffk at apple dot com>]

"Dave Korn" <dave.korn@artimi.com> writes:

> On 23 August 2007 22:34, Mark Mitchell wrote:
> 
> > I do think that generating the same code, independent of host system, is
> > a very important property of GCC's design, just like generating the same
> > code independent of whether or not we're compiling with -g.  
> 
>   Hear, hear.  I've always thought these principles were meant to be
> sacrosanct, but now I try to look it up, I don't see them explicitly
> listed in either the development methodology, the release criteria,
> or anywhere else likely-looking.
> 
>   Can the SC please consider adding these requirements explicitly to
> the list of "Design and Development Goals" in the mission statement?
> Or would it make more sense as part of the development methodology,
> or the portability section of the gcc-specific coding conventions?
> (Perhaps both; as a high-level goal in the mission statement, and
> with additions to the portability section of the coding conventions
> warning about issues like HOST_WIDE_INT size on 32-vs-64-bit hosts
> and not using pointers in hashes.)

As far as I know, this actually isn't a property of GCC's design, at
present.

Although the code generated is equivalent, there are a number of cases
where it is not exactly the same.  I don't remember them all, but one
case was that in many places the code does something like:

some_function(gen_reg_rtx(), gen_reg_rtx());

and so details of the RTL generated depend on the order of evaluation
of function arguments.  This was a big problem before we had GIMPLE,
and may still be an issue.