handle circular function reference gracefully

[alexlamsl]

fixes #2442

/cc @kzc

[alexlamsl]

@kzc I'm trying to come up with a test that resembles real code - for instance, this works just fine without this PR:

console.log(function factorial(n) {
    return n ? n * factorial(n - 1) : 1;
}(10));

[kzc]

I don't think it's possible to come up with an example of single-use function cycles in non-dead code.

[alexlamsl]

FWIW I've managed to sneak in just under 1MFuzz on current master, so once this gets merged I'll go spend ~30 minutes of ufuzz.js, then if nothing happens cut uglify-js@3.1.8

[alexlamsl]

110kFuzz passed without incident.

node test/benchmark.js

v3.1.7

bbedbf4

https://code.jquery.com/jquery-3.2.1.js - parse: 0.218s - scope: 0.173s - compress: 1.015s - mangle: 0.125s - properties: 0.000s - output: 0.125s - total: 1.656s Original: 268039 bytes Uglified: 86649 bytes GZipped: 30303 bytes SHA1 sum: 6c6d35d1d0bb687f154f92c244b92732f757cc0e https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.6.4/angular.js - parse: 0.421s - scope: 0.250s - compress: 1.922s - mangle: 0.266s - properties: 0.000s - output: 0.141s - total: 3.000s Original: 1249863 bytes Uglified: 173799 bytes GZipped: 60312 bytes SHA1 sum: 5019b726d625a60b04c70970f0a7219fb0c16eb8 https://cdnjs.cloudflare.com/ajax/libs/mathjs/3.9.0/math.js - parse: 0.796s - scope: 0.391s - compress: 3.500s - mangle: 0.344s - properties: 0.000s - output: 0.312s - total: 5.343s Original: 1590107 bytes Uglified: 467114 bytes GZipped: 118668 bytes SHA1 sum: 148315009a072f17e11a100f7b1f66834a44d97f https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.js - parse: 0.093s - scope: 0.062s - compress: 0.360s - mangle: 0.078s - properties: 0.000s - output: 0.047s - total: 0.640s Original: 69707 bytes Uglified: 36833 bytes GZipped: 9683 bytes SHA1 sum: bf8c46ddfb05ad98cd4e148038849b5bf2de3fe8 https://unpkg.com/react@15.3.2/dist/react.js - parse: 0.453s - scope: 0.265s - compress: 1.516s - mangle: 0.281s - properties: 0.000s - output: 0.156s - total: 2.671s Original: 701412 bytes Uglified: 205401 bytes GZipped: 61961 bytes SHA1 sum: df7f3652caa67e76f7c2c29679c296580dcd7254 http://builds.emberjs.com/tags/v2.11.0/ember.prod.js - parse: 0.750s - scope: 0.516s - compress: 2.734s - mangle: 0.343s - properties: 0.000s - output: 0.297s - total: 4.640s Original: 1852178 bytes Uglified: 526197 bytes GZipped: 128344 bytes SHA1 sum: 709c512d932fa559b4fa658b2c06ac543ec4e550 https://cdn.jsdelivr.net/lodash/4.17.4/lodash.js - parse: 0.265s - scope: 0.188s - compress: 1.547s - mangle: 0.109s - properties: 0.000s - output: 0.141s - total: 2.250s Original: 539590 bytes Uglified: 69910 bytes GZipped: 24405 bytes SHA1 sum: aff3d8636e0551decdac2733b14de75b4162303e https://cdnjs.cloudflare.com/ajax/libs/d3/4.5.0/d3.js - parse: 0.531s - scope: 0.328s - compress: 2.359s - mangle: 0.250s - properties: 0.000s - output: 0.172s - total: 3.640s Original: 451131 bytes Uglified: 211001 bytes GZipped: 70248 bytes SHA1 sum: 746cbefc1bb57d73f2f31d642f4fda32ea8e9f15

https://code.jquery.com/jquery-3.2.1.js - parse: 0.250s - compress: 1.125s - scope: 0.078s - mangle: 0.140s - properties: 0.000s - output: 0.141s - total: 1.734s Original: 268039 bytes Uglified: 86653 bytes GZipped: 30303 bytes SHA1 sum: 6e93d7851761a6c473e32a92f8247d8310e294e5 https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.6.4/angular.js - parse: 0.453s - compress: 2.172s - scope: 0.078s - mangle: 0.234s - properties: 0.000s - output: 0.141s - total: 3.078s Original: 1249863 bytes Uglified: 173819 bytes GZipped: 60320 bytes SHA1 sum: 7ef60c3a68facf60a73679aa66fcb13c0a556e1f https://cdnjs.cloudflare.com/ajax/libs/mathjs/3.9.0/math.js - parse: 0.828s - compress: 3.859s - scope: 0.172s - mangle: 0.359s - properties: 0.000s - output: 0.313s - total: 5.531s Original: 1590107 bytes Uglified: 467118 bytes GZipped: 118675 bytes SHA1 sum: 3a633e675e5471d44eecb5de5e09e5d2b8c1f9ac https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.js - parse: 0.093s - compress: 0.407s - scope: 0.015s - mangle: 0.063s - properties: 0.000s - output: 0.047s - total: 0.625s Original: 69707 bytes Uglified: 36833 bytes GZipped: 9683 bytes SHA1 sum: bf8c46ddfb05ad98cd4e148038849b5bf2de3fe8 https://unpkg.com/react@15.3.2/dist/react.js - parse: 0.375s - compress: 1.687s - scope: 0.078s - mangle: 0.172s - properties: 0.000s - output: 0.141s - total: 2.453s Original: 701412 bytes Uglified: 205436 bytes GZipped: 61964 bytes SHA1 sum: 5e1628192cdd3a963c849eba6340ba457cc20e9b http://builds.emberjs.com/tags/v2.11.0/ember.prod.js - parse: 0.828s - compress: 3.000s - scope: 0.187s - mangle: 0.344s - properties: 0.000s - output: 0.312s - total: 4.671s Original: 1852178 bytes Uglified: 526314 bytes GZipped: 128389 bytes SHA1 sum: f7f1873ca3cc0133533d35a02d4c44dc6a6bbe4b https://cdn.jsdelivr.net/lodash/4.17.4/lodash.js - parse: 0.250s - compress: 1.812s - scope: 0.078s - mangle: 0.141s - properties: 0.000s - output: 0.156s - total: 2.437s Original: 539590 bytes Uglified: 69889 bytes GZipped: 24396 bytes SHA1 sum: c1d197ecbbadf69ac46509041b54ae6bfc5401b5 https://cdnjs.cloudflare.com/ajax/libs/d3/4.5.0/d3.js - parse: 0.500s - compress: 2.671s - scope: 0.110s - mangle: 0.234s - properties: 0.000s - output: 0.172s - total: 3.687s Original: 451131 bytes Uglified: 210981 bytes GZipped: 70248 bytes SHA1 sum: 13b467b580fdff34806c5604a7de9f008d2b8149