Re: gcc compiler for pdp10

[Alan Lehotsky <apl at alum dot mit dot edu>]

Martin,

  I did a port of GCC to the Analog Devices SHARC chip.  I ended up  
supporting 3 kinds of pointers for this chip (two for address
spaces and one for byte pointers - the chip itself is only word  
addressable (although words can be from 16 to 48 bits in size
depending on what memory is being accessed.)

I also worked on the Bliss-36 compiler at DEC, so I'm well acquainted  
with the PDP10 architecture.

I don't have access to any 10/20 HW, but I'd be happy to act as a  
reviewer/advisor to your changes.

Al Lehotsky

On Apr 18, 2008, at 20:21, Martin Chaney wrote:

> Hi,
>
> I'm am the proprietor of a gcc compiler for the PDP10 architecture.
>
> (This is a compiler previously worked on by Lars Brinkhoff who left  
> XKL some while before I joined XKL.  It's possible some of you may  
> have been familiar with him or the compiler from that time.)
>
> The compiler is currently in a state where it is synched with the  
> both the 4.3 and 4.4 branches, and it passes the testsuite tests  
> (with the exception of some I've flagged as expected failures for  
> the pdp10).
>
> My employer is happy to release my work on the gcc compiler back to  
> the gcc community and I've sent in a request for the necessary forms.
>
> The PDP10 architecture is unusual in various ways that distinguish  
> it from the mainstream architectures supported by the gcc compiler  
> and this has made the development of this compiler a significant  
> task.  Undoubtedly I've made customizations in inappropriate ways.   
> I'm seeking contacts with people who might be able to advise me on  
> how to cleanup my implementation to reduce the amount of #ifdef  
> __PDP10_H__ I've sprinkled liberally throughout the source.  Also,  
> if its possible to get simple changes made to prevent breaking my  
> PDP10 version and that are otherwise innocuous that would be  
> wonderful.  For example, the PDP10 word size is 36 bits;  Fairly  
> recently people have taken to writing code that assumes word size  
> is a power of 2 even when it's straightforward to write in a manner  
> that doesn't make that assumption.
>
> Considering the large number of files customized to get the PDP10  
> compiler working, I'm not sure whether it's possible to get it to  
> build directly from the gcc trunk, but it would be nice to work  
> toward that goal.
>
> Some other things which distinguish the PDP10 architecture from  
> assumptions in the gcc code base include: its variety of formats of  
> pointers only one of which can be viewed as an integer and that one  
> is capable of referencing only word aligned data, a functional  
> difference between signed and unsigned integers, and peculiarities  
> to the use of PDP10 byte arrays which are very difficult to describe.
>
> Any help or advise would be appreciated.
>
> Martin Chaney
> XKL, LLC