[LLVMdev] Backend for the ZPU - a stack based / zero operand CPU

[Owen Anderson]

You might try looking at the recent work on PIC16.  If you look  
through the list archives, one of  the developers wrote about his  
experiences using LLVM for such a constrained architecture.  To  
summarize: while LLVM didn't offhand support the oddities of his  
architecture, it was easier to modifying to work with them than other  
compilers he had worked with.

--Owen

On Jun 19, 2008, at 2:30 PM, Øyvind Harboe wrote:

> Hi all,
>
> Zylin has implemented the world smallest 32 bit CPU with
> a GCC backend. (I shall stand corrected if anyone claims
> & proves otherwise :-)
>
> Implementing a GCC backend for a zero operand/stack based
> architecture proved pretty tricky, but I'm quite pleased with
> the resulting code. I did make alterations to the architecture
> to make it fit GCC without sacrificing CPU size.
>
> I have been following llvm.org from a distance, since I finished
> the GCC backend a couple of years back and there has not
> really been a reason to build a new compiler for the ZPU.
>
> My llvm.org knowledge is ... shallow ... but I'm hoping that
> someone would find the time & pity to answer my questions:
>
> Q: Is a stack based / zero operand CPU and llvm a good match? (GCC
> wasn't)
>
> Q: Should I expect better code density / performance from llvm than  
> GCC for
> said architecture?
>
> Q: Can llvm help move global data into flash(i.e. determine that  
> global C
> variables are in fact constants)?
>
>
> The ZPU would probably be most effective in highly space constrained
> applications(kBytes of code/data), such that it would fit entirely  
> onto
> an FPGA/CPLD. It has very high code density (~80% of ARM Thumb)
>
> Overview of architecture(documentation is definitely the weak side of
> the ZPU):
>
> http://www.zylin.com/zpu_arch.html
>
> The ZPU is now hosted at:
>
> http://www.opencores.org/projects.cgi/web/zpu/overview
>
> -- 
> Øyvind Harboe
> http://www.zylin.com/zy1000.html
> ARM7 ARM9 XScale Cortex
> JTAG debugger and flash programmer
>
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