Status: Accepted
Owner: ----
CC: [email protected]
Labels: Type-Bug Priority-Medium
New issue 3824 by [email protected]: Typed array maps should potentially
be immortal
https://code.google.com/p/v8/issues/detail?id=3824
The code below runs almost two times faster if line marked with (*) is
uncommented.
This happens because without that line GC constantly collects Typed Array
map, discards optimized version of the sieve and clears weak cell that
contains type feedback Data[i] keyed access sites.
When later sieve becomes hot again OSR happens in the first loop. At this
point second loop has 0 type information. Decisions in
HOptimizedGraphBuilder::HandleKeyedElementAccess are structured in way that
leads us to generate generic keyed access which is not prefix by a soft
HDeoptimize.
(this last problem can be perceived as a lack of proper type information
propagation - something that TF potentially will address)
function sieve(maxNum) {
var i;
var j;
var Data = new Uint8Array(maxNum + 1);
for (i=2; i<=maxNum; i++) {
Data[i] = 1;
}
for (i=2; i<=maxNum; i++) {
if (Data[i]) {
for (j=i+i; j<=maxNum; j+=i) {
Data[j] = 0; //
}
}
}
}
function measure(f, m) {
var start = Date.now();
for (var j = 0; j < m; j++) {
for (var i = 0; i < (1e3); i++) {
f(1e5);
}
}
var end = Date.now();
return (end - start);
}
// var arr = new Uint8Array(100); // (*)
measure(sieve, 2);
print(measure(sieve, 5));
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