Eyahlin wrote: ** and top-posted - fixed **
** He also snipped attribution for quoted material, not fixed **
>>
>> While the AST LCC IR is suitable for optimizations like algebraic
>> simplifications and CSE, it isn't generally very optimization
>> friendly. You are better off writing a tree walker and emit your 3-
>> address IR and write optimization p***** over them. In this case you
>> will obviously lose the retagetability lburg provides, but mapping 3-
>> address IR to DLX machine code should be fairly trivial. If you are
>> adventurous you can use lburg as your tree walker and experiment
>> writing an ir.md to emit your machine-independent 3-address IR into
>> memory(with a few hacks in emitcode() I think - sorry it was a long
>> time ago!). In this case, you still need to figure out how to create
>> BB and CFG - this will need modifications in reduce() - everytime you
>> hit a if-else or loop boundary etc you need to create new BB etc. You
>> can write your optimizations, coloring allocator, list scheduler etc
>> etc to work on this. All these are more hacks than clean solutions, so
>> I think writing a tree walker and a new optimizing back-end is the
>> best solution.
>>
>> Does gcc have an option to generate code for DLX? If so, you can write
>> a C generating back end for lcc - c.md and compile it using gcc. This
>> is only good if you need practice writing md files for lburg!
>
> Thanks for your ideas!
>
> I have learned essential lburg information. In fact, the MD
> specification for DLX is almost finished! Thanks! lburg is a great
> program.
>
> Your suggestion on rewriting a new tree walker is very convincing.
> Indeed, that will take care of the tightly-coupled LCC interface, and
> may even introduce global optimizations. Also, restructuring the DAGs
> to 3-address that the optimizations require allow easy manipulation
> and reordering of the code.
>
> However, my project is due in a few months. I think it's not feasible
> to rewrite essential phases of lcc over again, with the need to code
> advanced optimizations as well in such a short amount of time.
>
> Maybe there's a faster, or easier way to do it? I've chosen LCC for my
> front end because it's retargetable, and sup****ts a back end for MIPS,
> which is very similar to DLX. Also, a "do***entation" in the form of a
> book already exists, so I could learn about the design choices of the
> authors without needing to second-guess their intentions. However,
> problems arose when I tried to include optimizations. This is why I've
> originally asked for a way to *tap* the code list and not cause
> problems for the next phases after optimization. It's the most viable
> alternative that I could see while planning out the schedule for my
> project. But if there are other suggestions, I'm open to them.
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