Re: Docs for allocation sinking optimization
- From: Geoff Leyland <geoff_leyland@xxxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Wed, 18 Jul 2012 11:45:06 +1200
On 18/07/2012, at 11:31 AM, Mike Pall wrote:
> Geoff Leyland wrote:
>> Would it be interesting to ask "How many of the values
>> restored/replayed at trace exit are unused on-trace, and what
>> operation produced those values?".
>
> More interesting is whether the change would enable more
> allocations to be sunk or not. I'm not too worried about the
> simple add/sub operations themselves. E.g. (untested):
> luajit -jdump=i script.lua | egrep -c "}.*(TNEW|TDUP|CNEW|CNEWI)"
> with/without the patch.
Right. As I said, I'll keep at it bit by bit.
But my initial guess would be that it's not much use. Beyond the general
problem of not thinking enough about what I was doing, one of the reasons I was
fooled that the patch worked is that it wasn't doing anything. The SUBOV
problem wasn't related to it being a subtraction - it was just the first piece
of code (other than the very simple test case) I tested where it found
something to do. Most of the code I have just never triggers it.
If I get to the point that I'm confident that it works, and that it actually
seems to do something, then I'll see if it saves allocations.
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