Bug 55873 – Use HashMaps for caching primitive values

• Component: CSS
• Status: RESOLVED FIXED

[Antti Koivisto]

Both the memory efficiency and sharing efficiency of CSSPrimitiveValueCache can be improved by using HashMaps instead of fixed size arrays.

[Antti Koivisto]

Created attachment 84939 [details]
use HashMaps instead of fixed size arrays for caching

This removes the fixed per-document cost of empty cache (was ~10kb on 32bit)  while also somewhat improving caching efficiency (~5% from expanded integer range which more than pays for itself). Caches usually cover only a fraction of possible values so increased per-item cost from the hash table is ok.

[WebKit Review Bot]

Attachment 84939 [details] did not pass style-queue:

Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'Source/WebCore/ChangeLog', u'Source/WebCor..." exit_code: 1

Source/WebCore/css/CSSPrimitiveValueCache.cpp:97:  Tests for true/false, null/non-null, and zero/non-zero should all be done without equality comparisons.  [readability/comparison_to_zero] [5]
Source/WebCore/css/CSSPrimitiveValueCache.cpp:102:  Tests for true/false, null/non-null, and zero/non-zero should all be done without equality comparisons.  [readability/comparison_to_zero] [5]
Source/WebCore/css/CSSPrimitiveValueCache.cpp:107:  Tests for true/false, null/non-null, and zero/non-zero should all be done without equality comparisons.  [readability/comparison_to_zero] [5]
Total errors found: 3 in 3 files


If any of these errors are false positives, please file a bug against check-webkit-style.

Comment on attachment 84939 [details]
use HashMaps instead of fixed size arrays for caching

View in context: https://bugs.webkit.org/attachment.cgi?id=84939&action=review

> Source/WebCore/css/CSSPrimitiveValueCache.cpp:53
> +        m_identifierValueCache.add(ident, primitiveValue);

A get() followed by an add() means two cache lookups. You can do this with a single add().

[Sam Weinig]

Comment on attachment 84939 [details]
use HashMaps instead of fixed size arrays for caching

View in context: https://bugs.webkit.org/attachment.cgi?id=84939&action=review

> Source/WebCore/css/CSSPrimitiveValueCache.cpp:119
> +    RefPtr<CSSPrimitiveValue> primitiveValue = cache->get(intValue);
>      if (!primitiveValue) {
>          primitiveValue = CSSPrimitiveValue::create(value, type);
> -        m_integerValueCache[intValue][type] = primitiveValue;
> +        cache->add(intValue, primitiveValue);
>      }

Same comment as the the one mitz gave above. This can be done with one hash lookup.

[Antti Koivisto]

http://trac.webkit.org/changeset/80477 (with single hash lookups)

[WebKit Review Bot]

http://trac.webkit.org/changeset/80477 might have broken Qt Linux Release