157908 2016-05-19 12:11:10 -0700 arrow function lexical environment should reuse the same environment as the function's lexical environment where possible 2016-05-20 08:44:04 -0700 1 1 1 Unclassified WebKit JavaScriptCore WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED P2 Normal --- 1 saam saam benjamin cdumez fpizlo ggaren gskachkov keith_miller mark.lam msaboff oliver sukolsak ysuzuki oldest_to_newest 1194857 0 saam 2016-05-19 12:11:10 -0700 I removed this recently, but it causes a 7x regression in Sunspider/tofte which caused 5% regression in JetStream. It's probably valuable to reuse the same environment when possible for functions that use eval and have simple parameter lists. 1194867 1 279409 saam 2016-05-19 12:24:50 -0700 Created attachment 279409 patch 1194869 2 ggaren 2016-05-19 12:28:08 -0700 Sunspider/tofte uses arrow functions? 1194890 3 saam 2016-05-19 13:10:47 -0700 (In reply to comment #2) > Sunspider/tofte uses arrow functions? It uses eval. For example: function foo(x, y, z // Note: simple parameter list) { ... do some stuff eval(...) // Note must be direct eval ... do more stuff } My patch made such 'foo' functions slower. 1194891 4 saam 2016-05-19 13:10:58 -0700 landed in: http://trac.webkit.org/changeset/201176 1194896 5 saam 2016-05-19 13:13:06 -0700 (In reply to comment #3) > (In reply to comment #2) > > Sunspider/tofte uses arrow functions? > > It uses eval. > For example: > function foo(x, y, z // Note: simple parameter list) { > ... do some stuff > eval(...) // Note must be direct eval > ... do more stuff > } > > My patch made such 'foo' functions slower. To elaborate more, because we don't know what the eval will do, the eval may use arrow functions. So any function with a direct eval uses arrow functions. My previous patch made us always allocate a new environment for an arrow function's 'this', new.target, etc. But, this patch makes it so that we reuse the already created activation when doing so is sound. It's sound to do this when the function 'foo' has a simple parameter list. It's not sound to do this if it doesn't have a simple parameter list, i.e: function foo({a = ()=>this}) { ... eval(...) ... } 1195135 6 cdumez 2016-05-20 08:44:04 -0700 (In reply to comment #4) > landed in: > http://trac.webkit.org/changeset/201176 Confirmed 5% JetStream progression from this change on iOS. 279409 2016-05-19 12:24:50 -0700 2016-05-19 12:27:14 -0700 patch a-backup.diff text/plain 4739 saam SW5kZXg6IFNvdXJjZS9KYXZhU2NyaXB0Q29yZS9DaGFuZ2VMb2cKPT09PT09PT09PT09PT09PT09 PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PQotLS0gU291 cmNlL0phdmFTY3JpcHRDb3JlL0NoYW5nZUxvZwkocmV2aXNpb24gMjAxMTc1KQorKysgU291cmNl L0phdmFTY3JpcHRDb3JlL0NoYW5nZUxvZwkod29ya2luZyBjb3B5KQpAQCAtMSwzICsxLDE5IEBA CisyMDE2LTA1LTE5ICBTYWFtIGJhcmF0aSAgPHNiYXJhdGlAYXBwbGUuY29tPgorCisgICAgICAg IGFycm93IGZ1bmN0aW9uIGxleGljYWwgZW52aXJvbm1lbnQgc2hvdWxkIHJldXNlIHRoZSBzYW1l IGVudmlyb25tZW50IGFzIHRoZSBmdW5jdGlvbidzIGxleGljYWwgZW52aXJvbm1lbnQgd2hlcmUg 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