164531 2016-11-08 15:48:08 -0800 Spread(ArrayUse:@child) should participate in CSE 2018-01-19 13:41:35 -0800 1 1 1 Unclassified WebKit JavaScriptCore WebKit Nightly Build Unspecified Unspecified NEW P2 Normal --- 164258 1 saam saam benjamin ddkilzer fpizlo ggaren gskachkov jfbastien keith_miller mark.lam msaboff oliver ticaiolima ysuzuki oldest_to_newest 1249160 0 saam 2016-11-08 15:48:08 -0800 After I land https://bugs.webkit.org/show_bug.cgi?id=164258, we will emit Spread(ArrayUse:@child) only when we know that the iterator protocol is proven to be non-observable. This means we can CSE two Spread(ArrayUse:@child) together when we've proven that nobody changes @child in between the two Spreads. 1249162 1 saam 2016-11-08 15:48:53 -0800 It's important to also note that Spread will allocate a JSFixedArray, but JSFixedArray is a VM internal cell, it's not observable to user code. Therefore, it's ok to simply drop the second allocation and use the first one. 1391159 2 ddkilzer 2018-01-19 13:37:35 -0800 Since the comment mentioning this bug was removed in r227229, can this be changed to RESOLVED/WONTFIX? 1391162 3 saam 2018-01-19 13:41:35 -0800 (In reply to David Kilzer (:ddkilzer) from comment #2) > Since the comment mentioning this bug was removed in r227229, can this be > changed to RESOLVED/WONTFIX? I think it's worth keeping this. We could theoretically do this if we speculated in some particular way. Or if we proved the input to Spread doesn't have a symbol iterator.