[antlr-interest] ANTLR for a compiler

[Terence Parr]

Hi Bryan,

You want JBurg or something similar: a tree walker that is explicitly 
designed to generate code.  You can have ambiguous patterns with 
associated costs so that x+1 can be matched either as add one or 
increment.  here is a lab from my grad course where we generate machine 
code from an AST:

http://www.cs.usfca.edu/~parrt/course/652/labs/jburg.html

For example, I say:

JBurg descriptions looks like ANTLR tree grammars except that the 
parentheses are in a different spot (prefix vs postfix notation):

reg : #(ADD r1:reg r2:reg) {...emit instruction(s)...}

  and burg and friends use

reg : ADD(reg r1, reg r2) : 1 {...emit instruction(s)...}

where : 1 implies cost 1. Costs usually are just relative numbers but 
can mean "how many instructions were required?"

ANTLR tree walkers are not designed specifically for instruction 
selection; rather the opposite. :)  Building actual compilers has never 
been my focus (unless you count bytecode compilers, which are much 
easier).

Terence





 
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