[LLVMdev] What can llvm provide when writing a new compiler?

[David Greene]

On Wednesday 24 September 2008 02:27, Cloud Strife wrote:
> Hi everyone.
> Because there is still a little confusion about the huge document, I want
> to know what llvm can provide when we customize our new compiler?
> For example, a normal compiler includes lexer, parser, intermediate code
> generator , optimizer and target code generator. According to llvm
> documents, it seems that llvm can provide a better intermediate code
> presentation. And what else can it provide?

Codegen, codegen, codegen.

Oh, and optimizations too.  :)

>    Assuming my new lanuage is very unusual, should I write all the parts(
> lexer, parser, intermediate code generator , optimizer and target code
> generator) by myself? If so, is there any convenient method / scheme to do
> so? Because I heard that the biggest advantage of llvm is its flexible and
> quick-development for new language.

If you're targeting x86, for example, you do NOT want to write your own 
codegen!  If you do, good luck digesting five volumes of ISA material.  :)

This is generally true for other architectures as well.  Reuse, reuse, reuse.  
LLVM is well-designed to allow you to do that.  Take advantage of it.

Does LLVM have its shortcomings?  Sure.  But I can guarantee it has fewer 
shortcomings than a custom codegen would have down the road.  Because there's 
a community working on it, itr's been forced to be designed in a flexible and 
reuseable way.  Development process is a significant advantage of LLVM and 
open source in general, one that I think is greatly undervalued.

                                                        -Dave