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From: ghoti@BOURBAKI.MIT.EDU
Newsgroups: gnu.gcc
Subject: RTL Code and Debugging Tools
Message-ID: <8901101702.AA08812@hermite.mit.edu>
Date: 10 Jan 89 17:02:24 GMT
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In his interesting article, Patrick Paroubek tells us that he has 
separated the code generation from the rest of GCC in connection with
his work on the experimental language CLIP. He then presents excellent
arguments why it may not be such a good idea to do so in general. Of course,
the role it plays in his own research shows that it also sometimes IS a
good idea to separate the code generation part, as I am sure he will be the
first to agree. 

I would like to point out another reason why it might be a good idea.
Namely, there is presently no systematic way to debug GCC and the prospect
of being able to separate the various components of GCC and test them
individually is rather appealing. In particular, it would be desirable to
be able to separate the code generation from the rest of GCC and compile
directly from RTL.

Some people already know how to do this. Patrick is one of them. Also,
I received a message from Michael Tiemann some time ago saying that he
had also written such a thing and saying that he planned to release it
in the near future. I for one would be very interested in trying it out
when it does become available. 

Patrick also points out that the code generator doesn't accept all possible
RTL expressions, but only the ones likely to be produced from the source
language. This can be viewed as saying that the formal description of RTL
in the GCC documentation does not accurately describe the language actually
accepted by the code generator. Hence, it is natural to ask what must be 
added to the formal description of RTL to correct this situation.

Allan Adler
ghoti@hypatia.mit.edu