Optimise keyword arguments in the JIT

[markshannon]

Since the JIT traces can see both sides of the call, it can remove the work done to parse and shuffle the arguments during optimization.

For example, calling the function

def foo(a, b): pass

with keyword arguments:

foo(0, b=2, a=1)

requires the tuple ("b", "a") to pushed to the stack after the arguments
and for the CALL_KW_PY instruction to parse and reorder the arguments.

We can work out the reordering required and emit the necessary stack permuting code,
then replace the CALL_KW_PY with a much more effcient CALL_PY_EXACT_ARGS

In the example above:

LOAD_CONSTANT ("b", "a")
CALL_KW_PY 3

can be replaced with

SWAP 2
CALL_PY_EXACT_ARGS 3

Linked PRs

• gh-150724: Optimize JIT keyword calls to exact args #151389

[brijkapadia]

@markshannon Where would you put the optimization to switch bytecode instructions for the jit? After completing a trace, the jit will only see the uops, which would make it harder to do the proposed change for CALL_KW_PY.