117554 2013-06-12 11:40:39 -0700 DFG NewTypedArray should be a DCE candidate 2014-01-23 16:21:09 -0800 1 1 1 Unclassified WebKit JavaScriptCore 528+ (Nightly build) Unspecified OS X 10.8 UNCONFIRMED P2 Normal --- 0 evan.exe fpizlo fpizlo ggaren sergio oldest_to_newest 899645 0 evan.exe 2013-06-12 11:40:39 -0700 The attached page uses binary search to find the maximum size that the Uint8Array constructor accepts. In Firefox and Chrome the test completes in 4 seconds but with both Safari and WebKit Nightly the test takes 15 minutes and eats up 40gb of virtual memory. This is on a MacBook Air with 4gb of memory. 899649 1 204465 evan.exe 2013-06-12 11:42:39 -0700 Created attachment 204465 typed-array-limit.html 971380 2 ap 2014-01-23 16:03:48 -0800 Safari 7 says "Maximum is around 2048mb, found in 37.4 seconds". This is nowhere as horrible as before, but still still 10x slower than Firefox. ToT is about 20% slower on top of that. 971385 3 fpizlo 2014-01-23 16:19:58 -0800 I think that the title is a bit dramatic. I suspect that all that we're missing is the compiler smarts to eliminate the allocation of the typed array entirely. In this program, the statement: new Uint8Array(mid); is trivially dead code. Our optimizing compiler currently refuses to DCE typed array allocations because of (likely unfounded) paranoia about the typed array allocation having observable error checking. It probably has no observable error checking if the constructor is known to be passed an integer and that integer is non-negative. 204465 2013-06-12 11:42:39 -0700 2013-06-12 11:42:39 -0700 typed-array-limit.html typed-array-limit.html text/html 1117 evan.exe PGJvZHk+CiAgPHA+CiAgICBUaGlzIGZpZ3VyZXMgb3V0IHRoZSBzaXplIGxpbWl0IG9mIGEgc2lu Z2xlIHR5cGVkIGFycmF5IHVzaW5nIGJpbmFyeSBzZWFyY2guCiAgPC9wPgogIDx1bD4KICAgIDxs aT5DaHJvbWU6IDQ2MG1iIGluIDQgc2Vjb25kcyAoNzY4bWIgb24gYSBnb29kIGRheSk8L2xpPgog ICAgPGxpPkZpcmVmb3ggTmlnaHRseTogMjA0OG1iIGluIDQgc2Vjb25kcyAoYWN0dWFsIGxpbWl0 IGR1ZSB0byBzaWduZWQgMzItYml0IGludGVnZXJzIGZvciB0eXBlZCBhcnJheSBpbmRpY2VzKTwv bGk+CiAgICA8bGk+V2ViS2l0IE5pZ2h0bHk6IDIwNDhtYiBpbiA8Yj4xNSBtaW51dGVzPC9iPiAo ZWF0cyA8Yj40MGdiPC9iPiBvZiB2aXJ0dWFsIG1lbW9yeSk8L2xpPgogIDwvdWw+CjwvYm9keT4K PHNjcmlwdD4KCnZhciBtaW4gPSAwOwp2YXIgbWF4ID0gMHgxMDAwMDAwMDA7CnZhciBzdGFydCA9 IG5ldyBEYXRlOwoKZnVuY3Rpb24gbG9nKHRleHQpIHsKICB2YXIgZGl2ID0gZG9jdW1lbnQuY3Jl YXRlRWxlbWVudCgnZGl2Jyk7CiAgZGl2LnRleHRDb250ZW50ID0gdGV4dDsKICBkb2N1bWVudC5i b2R5LmFwcGVuZENoaWxkKGRpdik7Cn0KCmZ1bmN0aW9uIHRpY2soKSB7CiAgaWYgKG1pbiA9PT0g bWF4KSB7CiAgICBsb2coJ01heGltdW0gaXMgYXJvdW5kICcgKyAobWF4IC8gMTAyNCAvIDEwMjQp LnRvRml4ZWQoMCkgKyAnbWIsIGZvdW5kIGluICcgKyAoKG5ldyBEYXRlIC0gc3RhcnQpIC8gMTAw MCkudG9GaXhlZCgxKSArICcgc2Vjb25kcycpOwogICAgcmV0dXJuOwogIH0KCiAgdmFyIG1pZCA9 IE1hdGguZmxvb3IoKG1pbiArIG1heCkgLyAyKTsKICB2YXIgd29ya2VkID0gZmFsc2U7CgogIHRy eSB7CiAgICBuZXcgVWludDhBcnJheShtaWQpOwogICAgd29ya2VkID0gdHJ1ZTsKICB9IGNhdGNo IChlKSB7CiAgfQoKICBpZiAod29ya2VkKSBtaW4gPSBtaWQgKyAxOwogIGVsc2UgbWF4ID0gbWlk OwoKICBsb2coJzB4JyArIG1pZC50b1N0cmluZygxNikgKyAnIGJ5dGVzICcgKyAod29ya2VkID8g J3dvcmtlZCcgOiAnZGlkIG5vdCB3b3JrJykpOwogIHNldFRpbWVvdXQodGljaywgMTAwKTsKfQoK c2V0VGltZW91dCh0aWNrLCAxMDApOwoKPC9zY3JpcHQ+Cg==