[LLVMdev] Porting LLVM backend is no fun yet
greg at mcgary.org
Sat Apr 11 19:03:04 CDT 2009
As we've already seen, David Chisnall prefers hacking LLVM over GCC (see
http://www.informit.com/articles/article.aspx?p=1215438): "In contrast,
every time I look at the GCC code, it takes two people to
prevent me from clawing my eyeballs out."
I'm sorry to report that so-far I have had the opposite experience.
Some years ago, I ported binutils (via CGEN) and GCC to an embedded RISC
CPU and found it the process straightforward and pleasant. CGEN was
especially handy for describing a sometimes quirky RISC instruction set
and offered great flexibility for factoring-out commonalities. By
contrast, I have found TableGen to be much more rigid and brittle.
There are too many constructs that need to be special-cased, and the
existing ports do them in gratuitously different ways. There also seem
to be too many layers of classes and helper functions in proportion to
what's being specified. I guess that sums-up my gripe: low signal/noise
and gratuitous complexity. Sorry to be complaining rather than
proposing solutions. When I better get the hang of all of this, I
expect to have some ideas on how to improve TableGen. Is there a
development plan or wishlist for TableGen? I see nothing on the wiki yet.
I must also say that the LLVM code is considerably "denser" because of
the unfortunate choice of BiCapitalizedIdentifierNames. Underscores
lend some horizontal whitespace to names and make their subtokens
visually distict. BiCapped code is kinda like German with its
cumbersome compound nouns.
Enough complaining for now--back to banging skull on stone! 8^)
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