Feature Request

[Fergus Henderson]

On 06-Nov-2002, L C <listcatcher@shaw.ca> wrote:
> 1) I don't think the ISO code and unecessary typecasting issues would be 
> a concern since the requested compiler switch would obviously not be the 
> default. You would have to intentionally enable it and therefore realize 
> the ramifications.

Nevertheless, adding a compiler switch like which changes the language
semantics means adding another "dialect" of C.  Having a proliferation
of different dialects leads to a number of difficulties, e.g. it makes
reusing existing code more difficult.  Hence it would be much nicer to
just get the compiler to optimize the code better, rather than creating
a new dialect.

> 2) I'm an experienced hardware/firmware developer and I'm afraid I 
> wouldn't have a clue how to write the backend code you are talking 
> about.

Well, you could have a look at the code for the IP 2022 backend.
Certainly it is true that writing or maintaining code like this
requires considerable understanding of GCC internals.  But this is
a better way of doing it.  It would IMHO be a bad idea to add a
compiler switch merely because no-one with the necessary expertise
to write a back-end optimization pass was willing to take on the task.

> A simple compiler switch would simplify matters greatly.

It would simplify some things, but at the expense of complicating other
things.  For example, adding such a compiler switch would make it more
difficult to test GCC.  The end result of that would be a compiler which
is overall less reliable and more difficult to maintain.

> 3) I think for a typical simple embedded systems program the savings 
> would be greater than your 2-2.5%. I changed one arithmetic calculation 
> on my AVR such that I casted every calc back to unsigned char and the 
> code to do the calculation went from about 14 bytes to 4. It would also 
> be especially valuable in interrupt service routines where small code 
> size is key.

For interrupt service routines it is easy enough to add the desired
casts manually, no?

-- 
Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.