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Use a stack-allocated buffer for when computing a small string hash.

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Using a 256-byte buffer avoids 99% of allocations across v8's top25
benchmark. This also leads to a significant performance increase on
speedometer, with a ~1.2% improvement on jQuery, ~1.3% on VanillaJS
and an overall ~0.4% improvement on the score.

Bug: v8:7555
Change-Id: Icd6fa07341eb989892431cb1e4995557e35c7a67
Reviewed-on: https://chromium-review.googlesource.com/971837
Commit-Queue: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52125}
This commit is contained in:
Lucas Furukawa Gadani 2018-03-21 15:50:55 -04:00 committed by Commit Bot
parent 9ca8d90b8b
commit ab21ced5cd
1 changed files with 18 additions and 4 deletions
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22
src/objects.cc
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@ -17096,12 +17096,22 @@ class StringTableNoAllocateKey : public StringTableKey {
special_flattening_ = true;
uint32_t hash_field = 0;
if (one_byte_) {
one_byte_content_ = new uint8_t[length];
if (V8_LIKELY(length <=
static_cast<int>(arraysize(one_byte_buffer_)))) {
one_byte_content_ = one_byte_buffer_;
} else {
one_byte_content_ = new uint8_t[length];
}
String::WriteToFlat(string, one_byte_content_, 0, length);
hash_field =
StringHasher::HashSequentialString(one_byte_content_, length, seed);
} else {
two_byte_content_ = new uint16_t[length];
if (V8_LIKELY(length <=
static_cast<int>(arraysize(two_byte_buffer_)))) {
two_byte_content_ = two_byte_buffer_;
} else {
two_byte_content_ = new uint16_t[length];
}
String::WriteToFlat(string, two_byte_content_, 0, length);
hash_field =
StringHasher::HashSequentialString(two_byte_content_, length, seed);
@ -17119,9 +17129,9 @@ class StringTableNoAllocateKey : public StringTableKey {
~StringTableNoAllocateKey() {
if (one_byte_) {
delete[] one_byte_content_;
if (one_byte_content_ != one_byte_buffer_) delete[] one_byte_content_;
} else {
delete[] two_byte_content_;
if (two_byte_content_ != two_byte_buffer_) delete[] two_byte_content_;
}
}
@ -17195,6 +17205,10 @@ class StringTableNoAllocateKey : public StringTableKey {
uint8_t* one_byte_content_;
uint16_t* two_byte_content_;
};
union {
uint8_t one_byte_buffer_[256];
uint16_t two_byte_buffer_[128];
};
};
} // namespace