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deps: backport 066747e from upstream V8
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This backport fixes a performance pathology in how arrays grow/shrink.

Fixes: #3538
V8-Commit: v8/v8@066747e
PR-URL: #4625
Reviewed-By: cjihrig - Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: targos - Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: indutny - Fedor Indutny <fedor.indutny@gmail.com>

Original commit message:
  Make sure that NormalizeElements and ShouldConvertToFastElements are …

  …based on the same values

  BUG=v8:4518
  LOG=n

  Review URL: https://codereview.chromium.org/1472293002

  Cr-Commit-Position: refs/heads/master@{#32265}
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ofrobots committed Jan 12, 2016
1 parent 138e1e5 commit 00148b3
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Showing 2 changed files with 13 additions and 6 deletions.
17 changes: 11 additions & 6 deletions deps/v8/src/elements.cc
Original file line number Diff line number Diff line change
Expand Up @@ -1071,13 +1071,18 @@ class FastElementsAccessor
}
int num_used = 0;
for (int i = 0; i < backing_store->length(); ++i) {
if (!backing_store->is_the_hole(i)) ++num_used;
// Bail out early if more than 1/4 is used.
if (4 * num_used > backing_store->length()) break;
}
if (4 * num_used <= backing_store->length()) {
JSObject::NormalizeElements(obj);
if (!backing_store->is_the_hole(i)) {
++num_used;
// Bail out if a number dictionary wouldn't be able to save at least
// 75% space.
if (4 * SeededNumberDictionary::ComputeCapacity(num_used) *
SeededNumberDictionary::kEntrySize >
backing_store->length()) {
return;
}
}
}
JSObject::NormalizeElements(obj);
}
}

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2 changes: 2 additions & 0 deletions deps/v8/src/objects.cc
Original file line number Diff line number Diff line change
Expand Up @@ -12226,6 +12226,8 @@ static bool ShouldConvertToFastElements(JSObject* object,

uint32_t dictionary_size = static_cast<uint32_t>(dictionary->Capacity()) *
SeededNumberDictionary::kEntrySize;

// Turn fast if the dictionary only saves 50% space.
return 2 * dictionary_size >= *new_capacity;
}

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