Status: New
Owner: ----
New issue 3813 by rsturg...@google.com: v8 fails to learn types of bit
twiddly function and deopts all over the place
https://code.google.com/p/v8/issues/detail?id=3813
I have a function (see repro below) which turns a pair of 32 bit numbers
(representing the low and high parts of a 64 bit int) into a variable
length byte encoding.
This function is called by several other functions and ends up inlined all
over the place. But this code repeatedly deopts until finally optimizations
are disabled (for callers as well as this function, due to the inlining).
This is a real bummer.
--------- begin repro
// lowBits and highBits are integers in the range [0, 2^32-1]
function writeVarInt(lowBits, highBits, buff) {
while (highBits > 0 || lowBits > 127) {
buff.push((lowBits & 0x7f) | 0x80);
lowBits = ((lowBits >>> 7) | (highBits << 25)) >>> 0;
highBits = highBits >>> 7;
}
buff.push(lowBits);
}
function writeVarIntHelper(lowBits, highBits, buff) {
writeVarInt(lowBits, highBits, buff);
}
function test() {
for (var i = 0; i < 10000; i++) {
var buff = [];
writeVarIntHelper(i, 0, buff);
writeVarIntHelper(0xffffffff, 0xffffffff, buff);
}
}
for (var j = 0; j < 100; j++) {
test();
}
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