Optimize property access evaluation

[jridgewell]

Given the input a.b.c.d.e.f, the previous code would call _eval 57 times when using unsafe (and 15 times when using normal):

1 a.b
2 a.b.c
3 a.b
4 a.b
5 a.b.c.d
6 a.b.c
7 a.b
8 a.b
9 a.b.c
10 a.b
11 a.b
12 a.b.c.d.e
13 a.b.c.d
14 a.b.c
15 a.b
16 a.b
17 a.b.c
18 a.b
19 a.b
20 a.b.c.d
21 a.b.c
22 a.b
23 a.b
24 a.b.c
25 a.b
26 a.b
27 a.b.c.d.e.f
28 a.b.c.d.e
29 a.b.c.d
30 a.b.c
31 a.b
32 a.b
33 a.b.c
34 a.b
35 a.b
36 a.b.c.d
37 a.b.c
38 a.b
39 a.b
40 a.b.c
41 a.b
42 a.b
43 a.b.c.d.e
44 a.b.c.d
45 a.b.c
46 a.b
47 a.b
48 a.b.c
49 a.b
50 a.b
51 a.b.c.d
52 a.b.c
53 a.b
54 a.b
55 a.b.c
56 a.b
57 a.b

The first optimization is to only call expression._eval(…) a single time per evaluation of a AST_PropAccess. We've already called it to determine if we're a nullish, so there's no reason to do it a second time in the unsafe path. This alone brings us down to 15 calls (this is the same as the old normal path):

1 a.b
2 a.b.c
3 a.b
4 a.b.c.d
5 a.b.c
6 a.b
7 a.b.c.d.e
8 a.b.c.d
9 a.b.c
10 a.b
11 a.b.c.d.e.f
12 a.b.c.d.e
13 a.b.c.d
14 a.b.c
15 a.b

But, we can do even better by avoiding the evaluation mid–chain. There's no reason to evaluation unless the evaluation comes from the top of the chain (the rightmost property access). If anything can be optimized, it can optimize while we descend one time from that point. This brings us to 6 evaluations:

1 a.b
2 a.b.c.d.e.f
3 a.b.c.d.e
4 a.b.c.d
5 a.b.c
6 a.b

(I'm not sure why that first one happens)

Fixes #1212

[fabiosantoscode]

Nice work, thanks! ❤️

[ChristophP]

Awesome thank you for responding so quickly ❤️