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Re: Register Allocation Algorithm..
- From: Joe Buck <Joe dot Buck at synopsys dot com>
- To: dberlin at dberlin dot org (Daniel Berlin)
- Cc: ritu at csa dot iisc dot ernet dot in (Ritu Sabharwal), gcc at gcc dot gnu dot org,wilson at redhat dot com (Jim Wilson)
- Date: Thu, 3 Oct 2002 14:55:03 -0700 (PDT)
- Subject: Re: Register Allocation Algorithm..
> >> what is the register allocation algorithm used in gcc-3.0, can
> >> you get us some reference paper/material on this.
On Thursday, October 3, 2002, at 03:19 PM, Jim Wilson wrote:
> It uses an ad hoc algorithm based on register lifetime and number of
> register uses. See the code for more details.
Daniel Berlin writes:
> It actually might be easier to just look up the major register
> allocator patents, and then think of what it would take to get around
> them, if you can't understand the code.
Right, previously we had to avoid patents.
> There is a new optional register allocator in the current development
> sources that uses graph-coloring algorithms. See the ra-*.c files and the
> -fnew-ra option.
Since the register allocator was written, we (the GCC project) have
obtained permission from IBM and Rice University to use their register
allocator software patents in GPL code (after complicated negotiations
between FSF/IBM/Rice lawyers), which makes possible the new register
allocator.