Bug 1429126 - Rejigger cached anonymous box styles to use a union. r=emilio

MozReview-Commit-ID: I2b3wILKwNp

layout/style/CachedAnonBoxStyles.cpp

@@ -0,0 +1,71 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIMemoryReporter.h"
+#include "mozilla/CachedAnonBoxStyles.h"
+#include "mozilla/ServoStyleContext.h"
+
+namespace mozilla {
+
+void
+CachedAnonBoxStyles::Insert(ServoStyleContext* aStyle)
+{
+  MOZ_ASSERT(aStyle);
+  MOZ_ASSERT(aStyle->IsInheritingAnonBox());
+
+  if (IsEmpty()) {
+    RefPtr<ServoStyleContext> s = aStyle;
+    mBits = reinterpret_cast<uintptr_t>(s.forget().take());
+    MOZ_ASSERT(!IsEmpty() && !IsIndirect());
+  } else if (IsIndirect()) {
+    AsIndirect()->AppendElement(aStyle);
+  } else {
+    IndirectCache* cache = new IndirectCache();
+    cache->AppendElement(dont_AddRef(AsDirect()));
+    cache->AppendElement(aStyle);
+    mBits = reinterpret_cast<uintptr_t>(cache) | 1;
+    MOZ_ASSERT(IsIndirect());
+  }
+}
+
+ServoStyleContext*
+CachedAnonBoxStyles::Lookup(nsAtom* aAnonBox) const
+{
+  MOZ_ASSERT(nsCSSAnonBoxes::IsInheritingAnonBox(aAnonBox));
+  if (IsIndirect()) {
+    for (auto& style : *AsIndirect()) {
+      if (style->GetPseudo() == aAnonBox) {
+        return style;
+      }
+    }
+
+    return nullptr;
+  }
+
+  ServoStyleContext* direct = AsDirect();
+  return direct && direct->GetPseudo() == aAnonBox ? direct : nullptr;
+}
+
+void
+CachedAnonBoxStyles::AddSizeOfIncludingThis(nsWindowSizes& aSizes, size_t* aCVsSize) const
+{
+  if (IsIndirect()) {
+    for (auto& style : *AsIndirect()) {
+      if (!aSizes.mState.HaveSeenPtr(style)) {
+        style->AddSizeOfIncludingThis(aSizes, aCVsSize);
+      }
+    }
+
+    return;
+  }
+
+  ServoStyleContext* direct = AsDirect();
+  if (direct && !aSizes.mState.HaveSeenPtr(direct)) {
+    direct->AddSizeOfIncludingThis(aSizes, aCVsSize);
+  }
+}
+
+} // namespace mozilla

layout/style/CachedAnonBoxStyles.h

@@ -0,0 +1,67 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_CachedAnonBoxStyles_h
+#define mozilla_CachedAnonBoxStyles_h
+
+#include "nsAtom.h"
+#include "nsTArray.h"
+
+class nsWindowSizes;
+
+namespace mozilla {
+
+class ServoStyleContext;
+
+// Cache of anonymous box styles that inherit from a given style.
+//
+// To minimize memory footprint, the cache is word-sized with a tagged pointer
+// If there is only one entry, it's stored inline. If there are more, they're
+// stored in an out-of-line buffer. See bug 1429126 comment 0 and comment 1 for
+// the measurements and rationale that influenced the design.
+class CachedAnonBoxStyles
+{
+public:
+  void Insert(ServoStyleContext* aStyle);
+  ServoStyleContext* Lookup(nsAtom* aAnonBox) const;
+
+  CachedAnonBoxStyles() : mBits(0) {}
+  ~CachedAnonBoxStyles()
+  {
+    if (IsIndirect()) {
+      delete AsIndirect();
+    } else if (!IsEmpty()) {
+      RefPtr<ServoStyleContext> ref = dont_AddRef(AsDirect());
+    }
+  }
+
+  void AddSizeOfIncludingThis(nsWindowSizes& aSizes, size_t* aCVsSize) const;
+
+private:
+  // See bug 1429126 comment 1 for the choice of four here.
+  typedef AutoTArray<RefPtr<ServoStyleContext>, 4> IndirectCache;
+
+  bool IsEmpty() const { return !mBits; }
+  bool IsIndirect() const { return (mBits & 1); }
+
+  ServoStyleContext* AsDirect() const
+  {
+    MOZ_ASSERT(!IsIndirect());
+    return reinterpret_cast<ServoStyleContext*>(mBits);
+  }
+
+  IndirectCache* AsIndirect() const
+  {
+    MOZ_ASSERT(IsIndirect());
+    return reinterpret_cast<IndirectCache*>(mBits & ~1);
+  }
+
+  uintptr_t mBits;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_CachedAnonBoxStyles_h

layout/style/ServoStyleContext.cpp

@@ -33,26 +33,6 @@ ServoStyleContext::ServoStyleContext(
   // producing the ServoComputedData.
 }
 
-ServoStyleContext*
-ServoStyleContext::GetCachedInheritingAnonBoxStyle(nsAtom* aAnonBox) const
-{
-  MOZ_ASSERT(nsCSSAnonBoxes::IsInheritingAnonBox(aAnonBox));
-
-  // See the reasoning in SetCachedInheritingAnonBoxStyle to understand why we
-  // can't use the cache in this case.
-  if (IsInheritingAnonBox()) {
-    return nullptr;
-  }
-
-  auto* current = mNextInheritingAnonBoxStyle.get();
-
-  while (current && current->GetPseudo() != aAnonBox) {
-    current = current->mNextInheritingAnonBoxStyle.get();
-  }
-
-  return current;
-}
-
 ServoStyleContext*
 ServoStyleContext::GetCachedLazyPseudoStyle(CSSPseudoElementType aPseudo) const
 {

layout/style/ServoStyleContext.h

@@ -12,6 +12,8 @@
 #include "nsWindowSizes.h"
 #include <algorithm>
 
+#include "mozilla/CachedAnonBoxStyles.h"
+
 namespace mozilla {
 
 namespace dom {
@@ -45,26 +47,29 @@ public:
            !nsCSSPseudoElements::IsEagerlyCascadedInServo(GetPseudoType());
   }
 
-  ServoStyleContext* GetCachedInheritingAnonBoxStyle(nsAtom* aAnonBox) const;
+  ServoStyleContext* GetCachedInheritingAnonBoxStyle(nsAtom* aAnonBox) const
+  {
+    MOZ_ASSERT(nsCSSAnonBoxes::IsInheritingAnonBox(aAnonBox));
+
+    // This restriction is no longer necessary. We remove it in the next patch.
+    if (IsInheritingAnonBox()) {
+      return nullptr;
+    }
+
+    return mInheritingAnonBoxStyles.Lookup(aAnonBox);
+  }
 
   void SetCachedInheritedAnonBoxStyle(nsAtom* aAnonBox,
                                       ServoStyleContext* aStyle)
   {
     MOZ_ASSERT(!GetCachedInheritingAnonBoxStyle(aAnonBox));
-    MOZ_ASSERT(!aStyle->mNextInheritingAnonBoxStyle);
 
-    // NOTE(emilio): Since we use it to cache inheriting anon boxes in a linked
-    // list, we can't use that cache if the style we're inheriting from is an
-    // inheriting anon box itself, since otherwise our parent would mistakenly
-    // think that the style we're caching inherits from it.
-    //
-    // See the documentation of mNextInheritingAnonBoxStyle.
+    // This restriction is no longer necessary. We remove it in the next patch.
     if (IsInheritingAnonBox()) {
       return;
     }
 
-    mNextInheritingAnonBoxStyle.swap(aStyle->mNextInheritingAnonBoxStyle);
-    mNextInheritingAnonBoxStyle = aStyle;
+    mInheritingAnonBoxStyles.Insert(aStyle);
   }
 
   ServoStyleContext* GetCachedLazyPseudoStyle(CSSPseudoElementType aPseudo) const;
@@ -111,11 +116,7 @@ public:
     // clearly identify in DMD's output the memory measured here.
     *aCVsSize += ServoComputedValuesMallocEnclosingSizeOf(this);
     mSource.AddSizeOfExcludingThis(aSizes);
-
-    if (mNextInheritingAnonBoxStyle &&
-        !aSizes.mState.HaveSeenPtr(mNextInheritingAnonBoxStyle)) {
-      mNextInheritingAnonBoxStyle->AddSizeOfIncludingThis(aSizes, aCVsSize);
-    }
+    mInheritingAnonBoxStyles.AddSizeOfIncludingThis(aSizes, aCVsSize);
 
     if (mNextLazyPseudoStyle &&
         !aSizes.mState.HaveSeenPtr(mNextLazyPseudoStyle)) {
@@ -127,12 +128,9 @@ private:
   nsPresContext* mPresContext;
   ServoComputedData mSource;
 
-  // A linked-list cache of inheriting anon boxes inheriting from this style _if
-  // the style isn't an inheriting anon-box_.
-  //
-  // Otherwise it represents the next entry in the cache of the parent style
-  // context.
-  RefPtr<ServoStyleContext> mNextInheritingAnonBoxStyle;
+  // A cache of inheriting anon boxes inheriting from this style _if the style
+  // isn't an inheriting anon-box_.
+  CachedAnonBoxStyles mInheritingAnonBoxStyles;
 
   // A linked-list cache of lazy pseudo styles inheriting from this style _if
   // the style isn't a lazy pseudo style itself_.

layout/style/moz.build

@@ -81,6 +81,7 @@ EXPORTS += [
 EXPORTS.mozilla += [
     'AnimationCollection.h',
     'BindingStyleRule.h',
+    'CachedAnonBoxStyles.h',
     'CSSEnabledState.h',
     'CSSStyleSheet.h',
     'CSSVariableDeclarations.h',
@@ -179,6 +180,7 @@ EXPORTS.mozilla.css += [
 UNIFIED_SOURCES += [
     'AnimationCollection.cpp',
     'BindingStyleRule.cpp',
+    'CachedAnonBoxStyles.cpp',
     'CounterStyleManager.cpp',
     'CSS.cpp',
     'CSSFontFeatureValuesRule.cpp',