improve compression of undefined, NaN & Infinitiy

[alexlamsl]

Maintains identical behaviour, but move all the transformation logic from OutputStream to Compressor.

Next up would be to implement #1730.

@kzc if you want Infinity ➡️ 1/0 & undefined ➡️ void 0 to be gated behind a new flag (default enabled), mind coming up with a good name for it? 😅

[kzc]

if you want Infinity ➡️ 1/0 & undefined ➡️ void 0 to be gated behind a new flag (default enabled)

So, just to confirm - NaN will always remain NaN?

I think undefined ➡️ void 0 should always take place as it presently does in the Compressor as there is no size or speed disadvantage - unless it's one of those crazy cases where it's a redefined variable name.

That just leaves Infinity vs. 1/0. How about the unambiguous option name keep_infinity?

[alexlamsl]

So, just to confirm - NaN will always remain NaN ?

NaN will always remain NaN unless when a locally defined variable named NaN exists, in which case it will indiscriminately turned into 0/0 to avoid the bug.

I think undefined ➡️ void 0 should always take place as it presently does in the Compressor as there is no size or speed disadvantage

So that Chrome performance degradation only applies to NaN and Infinity but not undefined? If so, yeah, I'll just gate with keep_inf (or keep_infinity in case anybody gets funny ideas about .INF files).

[alexlamsl]

And to clarify, I think the forced NaN ➡️ 0/0 is okay because it will be converted from things like +"foo", and so:

• even with parenthesis the representation should be shorter
• performance of things like Infinity * null would probably be comparable to 0/0 anyway

[alexlamsl]

Current PR passed half a mega-fuzz without incident.

Proceed with Phase 2. 😎

[kzc]

So that Chrome performance degradation only applies to NaN and Infinity but not undefined?

As far as I know. void 0 a common pattern that they would optimize because of the widespread use of minifiers.

[kzc]

@alexlamsl Kudos for the elimination of PARENS([ AST_Infinity, AST_NaN ], DEFPRINT(AST_Undefined, DEFPRINT(AST_Infinity and DEFPRINT(AST_NaN. The code is a lot cleaner with this PR. Everything is in the correct place.

$ echo 'console.log(undefined, Infinity, NaN);' | bin/uglifyjs -c
console.log(void 0,1/0,NaN);

$ echo 'console.log(undefined, Infinity, NaN);' | bin/uglifyjs -c keep_infinity
console.log(void 0,Infinity,NaN);

+1

[alexlamsl]

@kzc glad you like it 😉