[LLVMdev] Proposal for new Legalization framework

[Diego Novillo]

On 2013-04-26 14:43 , Chris Lattner wrote:
> There definitely are strong advantages to using one datastructure to represent multiple levels of IR: you have less code in the compiler, more shared concepts, etc.  I have seen and work with several compilers that tried to do this.  Even GCC does this (in the opposite direction) with "treessa" which repurposes some front-end data structures for their mid-level IR.

Note that this was a transitional step only.  Nowadays GIMPLE is its own 
data structure.  It still keeps pointers to the tree data structure for 
symbols and types.  But eventually, if the existing plans materialize, 
these will be converted into proper indexes into symbol and type tables.

Over time, we have found that there is a distinct advantage in having 
different internal types represent different IRs.  The division of 
responsibilities is easier to express.  Making this distinction in GCC's 
codebase is less than trivial, however.

There are some data structures that are advantageous to share across 
IRs.  Mostly container types like CFG, call graph, loop structures, etc.


Diego.