Re: Global analysis of RTL

[Geoff Wozniak <gcc at geoff dot wozniak dot ca>]

R0b0t1 <r030t1@gmail.com> writes:
> When I first looked at the GCC codebase, it seemed to me that 
> most operations should be done on the GIMPLE representation as 
> it contains the most information. Is there any reason you 
> gravitated towards RTL? 

Naiveté, really.

My team and I didn’t know much about the code base when we started 
looking at the problem, although we knew a little about the 
intermediate formats. GIMPLE makes the analysis more complicated, 
although not impossible, and it can make the cost model difficult 
to pin down. Raw assembly/machine code is ideal, but then we have 
to deal with different platforms and would likely have to do all 
the work in the linker. RTL is sufficiently low-level enough (as 
far as we know) to start counting instructions, and platform 
independent enough that we don’t have to parse machine code.

Essentially, working with RTL makes the implementation a little 
easier but we didn’t know that the pass infrastructure wasn’t in 
our favour.

It’s likely we’ll turn our attention to GIMPLE and 
assembler/machine code, unless we can come up with something (or 
anyone has a suggestion).

-- Geoff