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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/286494">286494</a></dd>
<dt>Author</dt> <dd>antti@apple.com</dd>
<dt>Date</dt> <dd>2021-12-03 09:10:13 -0800 (Fri, 03 Dec 2021)</dd>
</dl>

<h3>Log Message</h3>
<pre>[:has() pseudo-class] Improve result caching
https://bugs.webkit.org/show_bug.cgi?id=233806

Reviewed by Simon Fraser.

Improve caching to to avoid O(n^2) cases during invalidation and style resolution.

* css/SelectorChecker.cpp:
(WebCore::SelectorChecker::matchHasPseudoClass const):

Cache matches as well as failures.
Cache failures that don't apply to subtrees.
Check cached matches and failures for all :has() match element types.

* style/SelectorMatchingState.h:</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCorecssSelectorCheckercpp">trunk/Source/WebCore/css/SelectorChecker.cpp</a></li>
<li><a href="#trunkSourceWebCorestyleSelectorMatchingStateh">trunk/Source/WebCore/style/SelectorMatchingState.h</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (286493 => 286494)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog   2021-12-03 17:08:36 UTC (rev 286493)
+++ trunk/Source/WebCore/ChangeLog      2021-12-03 17:10:13 UTC (rev 286494)
</span><span class="lines">@@ -1,3 +1,21 @@
</span><ins>+2021-12-03  Antti Koivisto  <antti@apple.com>
+
+        [:has() pseudo-class] Improve result caching
+        https://bugs.webkit.org/show_bug.cgi?id=233806
+
+        Reviewed by Simon Fraser.
+
+        Improve caching to to avoid O(n^2) cases during invalidation and style resolution.
+
+        * css/SelectorChecker.cpp:
+        (WebCore::SelectorChecker::matchHasPseudoClass const):
+
+        Cache matches as well as failures.
+        Cache failures that don't apply to subtrees.
+        Check cached matches and failures for all :has() match element types.
+
+        * style/SelectorMatchingState.h:
+
</ins><span class="cx"> 2021-12-03  Alex Christensen  <achristensen@webkit.org>
</span><span class="cx"> 
</span><span class="cx">         Add room for more bytecode in WKContentRuleList file format
</span></span></pre></div>
<a id="trunkSourceWebCorecssSelectorCheckercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/css/SelectorChecker.cpp (286493 => 286494)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/css/SelectorChecker.cpp     2021-12-03 17:08:36 UTC (rev 286493)
+++ trunk/Source/WebCore/css/SelectorChecker.cpp        2021-12-03 17:10:13 UTC (rev 286494)
</span><span class="lines">@@ -1249,8 +1249,22 @@
</span><span class="cx"> 
</span><span class="cx"> bool SelectorChecker::matchHasPseudoClass(CheckingContext& checkingContext, const Element& element, const CSSSelector& hasSelector) const
</span><span class="cx"> {
</span><del>-    // FIXME: This could be better in terms of performance.
</del><ins>+    auto* cache = checkingContext.selectorMatchingState ? &checkingContext.selectorMatchingState->hasPseudoClassMatchCache : nullptr;
</ins><span class="cx"> 
</span><ins>+    Style::HasPseudoClassMatch* cachedMatch = nullptr;
+    if (cache) {
+        cachedMatch = &cache->add(Style::makeHasPseudoClassCacheKey(hasSelector, element), Style::HasPseudoClassMatch::None).iterator->value;
+        switch (*cachedMatch) {
+        case Style::HasPseudoClassMatch::Matches:
+            return true;
+        case Style::HasPseudoClassMatch::Fails:
+        case Style::HasPseudoClassMatch::FailsSubtree:
+            return false;
+        case Style::HasPseudoClassMatch::None:
+            break;
+        }
+    }
+
</ins><span class="cx">     SelectorChecker hasChecker(element.document());
</span><span class="cx">     bool matchedInsideScope = false;
</span><span class="cx"> 
</span><span class="lines">@@ -1267,69 +1281,90 @@
</span><span class="cx">     };
</span><span class="cx"> 
</span><span class="cx">     auto checkDescendants = [&](const Element& descendantRoot) {
</span><del>-        auto descendants = descendantsOfType<Element>(descendantRoot);
-        if (!descendants.first())
-            return false;
-
-        if (checkingContext.selectorMatchingState) {
-            // See if we already know this :has() selector doesn't match in this subtree.
-            auto& failureCache = checkingContext.selectorMatchingState->hasPseudoClassDescendantFailureCache;
-            if (!failureCache.isEmpty()) {
-                for (auto* ancestor = descendantRoot.parentElement(); ancestor; ancestor = ancestor->parentElement()) {
-                    if (failureCache.contains(Style::makeHasPseudoClassCacheKey(hasSelector, *ancestor)))
-                        return false;
</del><ins>+        for (auto it = descendantsOfType<Element>(descendantRoot).begin(); it;) {
+            auto& descendant = *it;
+            if (cache) {
+                auto key = Style::makeHasPseudoClassCacheKey(hasSelector, descendant);
+                if (cache->get(key) == Style::HasPseudoClassMatch::FailsSubtree) {
+                    it.traverseNextSkippingChildren();
+                    continue;
</ins><span class="cx">                 }
</span><span class="cx">             }
</span><del>-        }
-
-        matchedInsideScope = false;
-
-        for (auto& descendant : descendants) {
</del><span class="cx">             if (checkRelative(descendant))
</span><span class="cx">                 return true;
</span><del>-        }
</del><span class="cx"> 
</span><del>-        if (checkingContext.selectorMatchingState && !matchedInsideScope) {
-            auto& failureCache = checkingContext.selectorMatchingState->hasPseudoClassDescendantFailureCache;
-            failureCache.add(Style::makeHasPseudoClassCacheKey(hasSelector, descendantRoot));
</del><ins>+            it.traverseNext();
</ins><span class="cx">         }
</span><span class="cx"> 
</span><span class="cx">         return false;
</span><span class="cx">     };
</span><span class="cx"> 
</span><del>-    auto matchElement = Style::computeHasPseudoClassMatchElement(hasSelector);
</del><ins>+    auto match = [&] {
+        auto matchElement = Style::computeHasPseudoClassMatchElement(hasSelector);
</ins><span class="cx"> 
</span><del>-    switch (matchElement) {
-    case Style::MatchElement::HasChild:
-        for (auto& child : childrenOfType<Element>(element)) {
-            if (checkRelative(child))
</del><ins>+        switch (matchElement) {
+        // :has(> .child)
+        case Style::MatchElement::HasChild:
+            for (auto& child : childrenOfType<Element>(element)) {
+                if (checkRelative(child))
+                    return true;
+            }
+            break;
+        // :has(.descendant)
+        case Style::MatchElement::HasDescendant: {
+            if (!element.firstElementChild())
+                return false;
+            if (cache) {
+                // See if we already know this descendant selector doesn't match in this subtree.
+                for (auto* ancestor = element.parentElement(); ancestor; ancestor = ancestor->parentElement()) {
+                    auto key = Style::makeHasPseudoClassCacheKey(hasSelector, *ancestor);
+                    if (cache->get(key) == Style::HasPseudoClassMatch::FailsSubtree)
+                        return false;
+                }
+            }
+            if (checkDescendants(element))
</ins><span class="cx">                 return true;
</span><ins>+            break;
</ins><span class="cx">         }
</span><del>-        break;
-    case Style::MatchElement::HasDescendant: {
-        if (checkDescendants(element))
-            return true;
-        break;
-    }
-    case Style::MatchElement::HasSibling:
-        for (auto* sibling = element.nextElementSibling(); sibling; sibling = sibling->nextElementSibling()) {
-            if (checkRelative(*sibling))
-                return true;
</del><ins>+        // FIXME: Add a separate case for adjacent combinator.
+        // :has(+ .sibling)
+        // :has(~ .sibling)
+        case Style::MatchElement::HasSibling:
+            for (auto* sibling = element.nextElementSibling(); sibling; sibling = sibling->nextElementSibling()) {
+                if (checkRelative(*sibling))
+                    return true;
+            }
+            break;
+        // FIXME: Add a separate case for adjacent combinator.
+        // :has(+ .sibling .descendant)
+        // :has(~ .sibling .descendant)
+        case Style::MatchElement::HasSiblingDescendant:
+            for (auto* sibling = element.nextElementSibling(); sibling; sibling = sibling->nextElementSibling()) {
+                if (checkDescendants(*sibling))
+                    return true;
+            }
+            break;
+
+        default:
+            ASSERT_NOT_REACHED();
+            break;
</ins><span class="cx">         }
</span><del>-        break;
-    case Style::MatchElement::HasSiblingDescendant:
-        for (auto* sibling = element.nextElementSibling(); sibling; sibling = sibling->nextElementSibling()) {
-            if (checkDescendants(*sibling))
-                return true;
-        }
-        break;
</del><ins>+        return false;
+    };
</ins><span class="cx"> 
</span><del>-    default:
-        ASSERT_NOT_REACHED();
-        break;
</del><ins>+    auto result = match();
+
+    if (cachedMatch) {
+        *cachedMatch = [&] {
+            if (result)
+                return Style::HasPseudoClassMatch::Matches;
+            if (matchedInsideScope)
+                return Style::HasPseudoClassMatch::Fails;
+            return Style::HasPseudoClassMatch::FailsSubtree;
+        }();
</ins><span class="cx">     }
</span><span class="cx"> 
</span><del>-    return false;
</del><ins>+    return result;
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> bool SelectorChecker::checkScrollbarPseudoClass(const CheckingContext& checkingContext, const Element& element, const CSSSelector& selector) const
</span></span></pre></div>
<a id="trunkSourceWebCorestyleSelectorMatchingStateh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/style/SelectorMatchingState.h (286493 => 286494)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/style/SelectorMatchingState.h       2021-12-03 17:08:36 UTC (rev 286493)
+++ trunk/Source/WebCore/style/SelectorMatchingState.h  2021-12-03 17:10:13 UTC (rev 286494)
</span><span class="lines">@@ -25,15 +25,17 @@
</span><span class="cx"> #pragma once
</span><span class="cx"> 
</span><span class="cx"> #include "SelectorFilter.h"
</span><del>-#include <wtf/HashSet.h>
</del><ins>+#include <wtf/HashMap.h>
</ins><span class="cx"> 
</span><span class="cx"> namespace WebCore::Style {
</span><span class="cx"> 
</span><span class="cx"> using HasPseudoClassCacheKey = std::pair<const CSSSelector*, const Element*>;
</span><span class="cx"> 
</span><ins>+enum class HasPseudoClassMatch : uint8_t { None, Matches, Fails, FailsSubtree };
+
</ins><span class="cx"> struct SelectorMatchingState {
</span><span class="cx">     SelectorFilter selectorFilter;
</span><del>-    HashSet<HasPseudoClassCacheKey> hasPseudoClassDescendantFailureCache;
</del><ins>+    HashMap<HasPseudoClassCacheKey, HasPseudoClassMatch> hasPseudoClassMatchCache;
</ins><span class="cx"> };
</span><span class="cx"> 
</span><span class="cx"> inline HasPseudoClassCacheKey makeHasPseudoClassCacheKey(const CSSSelector& selector, const Element& element)
</span></span></pre>
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