1890491 - Speedup moz.build parsing

Status: NEW

(Firefox Build System :: General, task)

Description

[[:sergesanspaille]]

We spend several seconds in the configure step executing the moz.build files. It's worth checking if we could do that in a faster way.

Comment 1

[[:sergesanspaille]]

On possible approach, based on this session:

ssp@lakota:/tmp/py% cat fun.py 
def foo(x, y, z):
    x += [1]
    y = "foo"
    if z:
        x += [z]
        y += "bar"
    return x, y, z
ssp@lakota:/tmp/py% cat g.py 
x += [1]
y = "foo"
if z:
    x += [z]
    y += "bar"

ssp@lakota:/tmp/py% python -m timeit -s 'x = []; y = ""; z = 1; from fun import foo as fun' 'x, y, z = fun(x, y, z)' 
1000000 loops, best of 5: 207 nsec per loop
ssp@lakota:/tmp/py% python -m timeit -s 'x = []; y = ""; z = 1; obj = compile(open("g.py").read(), "<>", "exec")' 'exec(obj)'
500000 loops, best of 5: 752 nsec per loop

would be to automatically turn moz.build files into functions, so that we can benefit from faster variable access for function local variables instead of global variables.

Comment 2

[[:sergesanspaille]]

extra data point, with a scenario that would be closer to reality:

ssp@lakota:/tmp/py% python -m timeit -s 'x = []; y = ""; z = 1; obj = compile(open("fun.py").read(), "<>", "exec"); d={}' 'x, y, z = (exec(obj, d), d["foo"](x, y, z))[1]' 
500000 loops, best of 5: 442 nsec per loop