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Re: Worth balancing the tree before scheduling?
On Fri, Nov 20, 2009 at 10:05 AM, Ian Bolton <bolton@icerasemi.com> wrote:
> From some simple experiments (see below), it appears as though GCC aims
> to
> create a lop-sided tree when there are constants involved (func1 below),
> but a balanced tree when there aren't (func2 below).
>
> Our assumption is that GCC likes having constants all near to each other
> to
> aid with tree-based optimisations, but I'm fairly sure that, when it
> comes
> to scheduling, it would be better to have a balanced tree, so sched has
> more
> choices about what to schedule next?
I think this would depend on the target architecture and instruction
set: CISC vs RISC, many registers vs few registers, etc. I do not
believe that GCC intentionally is trying to optimize for either, but I
do not think there is a single, right answer.
David