Re: Graph colouring and local register allocation

On Sat, 1 Dec 2007 10:12:01 -0800 (PST), "preston.briggs@xxxxxxxxx"
<preston.briggs@xxxxxxxxx> wrote:

Frankly, I don't see what impact ILP has on register allocation [...]

If we schedule to minimize register pressure, then allocate, then try
to reschedule to maxmize ILP, we'll have a hard time. The initial
schedule and allocation will leave us very little "room to work". On
the other hand, if we initially schedule for maximum ILP, then
allocation will require more registers, perhaps causing spill code.

My point was that register allocation for ILP is not, as Sid Touati
seemed to be claiming, a fundamentally different problem from
allocating for a sequential processor. There is some additional
effort to iterate scheduling and allocation to find a good balance,
but existing methods are up to that task already (whether existing
compilers do as well as they could using them is a different
discussion).

New methods that reduce the effort to find the sweet spot are always
welcome, but IMO claiming the old methods can't do the job is just
wrong.


Google up "Register Allocation with Instruction Scheduling: A New
Approach" by Schlomit Pinter. That and the papers that cite it will
get you off to a good start.

I've seen that. Thanks.

George
.

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