[Python] Optimize Prepend: handle alignment and byte writes in one pass

[satur9nine]

Part 3 of 3

Optimize Prepend: handle alignment and byte writes in one pass

This is a break-up of #8766

Improves performance of the PythonTest over part 2 by 5.4%

python-perf-prep.txt
python-perf-prepend.txt

[fliiiix]

where is self.head = UOffsetTFlags.py_type(new_head) coming from in these changes? because i would expect self.Head() == self.head and Write itself did not change 😕

[satur9nine]

I'm not quite sure about you question, new_head is a local variable being used which should be faster than accessing fields self.head or function calls selfHead().

Or maybe you are asking why I added the call to UOffsetTFlags.py_type, to be honest I was shuffling a lot of code around and I saw that in existing code pretty much every time head is assigned it is having this function call on it, like in WriteVtable:

self.head = UOffsetTFlags.py_type(objectStart)

I should have looked closer and I see now that py_type is just int. So really all the XYZ.py_type calls in this code are basically converting to int but everything is already an integer so we don't need this call. I updated #8808 to avoid more casting and the improvements are even better and the code changes are cleaner too.

[fliiiix]

is this primary faster because it skips self.Pad(alignSize) ? I guess this is a value judgment if we want more performance or simpler code here - im fine with both

[satur9nine]

Yes exactly, calling Pad is what is making this original implementation expensive, inlining the implementations and avoiding Pad helps

[satur9nine]

After I improved #8808 I see this change really gives a very small bump for all that inlining, feel free to take it or drop it, the existing code is definitely more readable and most of the gains come from part 1 and 2.

[jtdavis777]

given this is such a small improvement I'm tempted to drop it -- especially with no commentary :)

[satur9nine]

Sure, most improvements come from the previous commits!

[fliiiix]

Neat i left a few comments but overall i think this can be merged 👍

[satur9nine]

Not significant improvement, #8807 and #8808 suffice.