From db8e759c6654a09aa851384768d580fb632b7274 Mon Sep 17 00:00:00 2001
From: Cameron McCormack <cam@mcc.id.au>
Date: Wed, 28 Jun 2017 09:27:30 -0400
Subject: [PATCH] Bug 1353312 - Don't use conditions when caching a struct with
 no rules. r=dbaron

MozReview-Commit-ID: 7yzG5vIKxwh
---
 layout/style/RuleNodeCacheConditions.h |  5 +++++
 layout/style/nsRuleNode.cpp            | 17 +++++++++++++++++
 layout/style/nsRuleNode.h              | 13 +++++++++----
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/layout/style/RuleNodeCacheConditions.h b/layout/style/RuleNodeCacheConditions.h
index a7f59365de43..4b1a2349a55a 100644
--- a/layout/style/RuleNodeCacheConditions.h
+++ b/layout/style/RuleNodeCacheConditions.h
@@ -95,6 +95,11 @@ public:
     mBits |= eUncacheable;
   }
 
+  void Clear()
+  {
+    *this = RuleNodeCacheConditions();
+  }
+
   bool Cacheable() const
   {
     return !(mBits & eUncacheable);
diff --git a/layout/style/nsRuleNode.cpp b/layout/style/nsRuleNode.cpp
index 2eea495a67ec..106c55699147 100644
--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -2673,6 +2673,23 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
   if (!highestNode)
     highestNode = rootNode;
 
+  if (detail == eRuleNone && isReset) {
+    // We specified absolutely no rule information for a reset struct, and we
+    // may or may not have found a parent rule in the tree that specified all
+    // the rule information.  Regardless, we don't need to use any cache
+    // conditions when we (inevitably) cache this struct in the rule tree.
+    //
+    // Normally ruleData.mConditions would already indicate that the struct
+    // is cacheable without conditions if detail is eRuleNone, but because
+    // of the UnsetPropertiesWithoutFlags call above, we may have encountered
+    // some rules with dependencies, which we then cleared out of ruleData.
+    NS_ASSERTION(ruleData.mConditions.CacheableWithoutDependencies() ||
+                 pseudoRestriction,
+                 "we should already be cacheable without dependencies if we "
+                 "didn't have a pseudo restriction");
+    ruleData.mConditions.Clear();
+  }
+
   MOZ_ASSERT(!(aSID == eStyleStruct_Variables && startStruct),
              "if we start caching Variables structs in the rule tree, then "
              "not forcing detail to eRulePartialMixed just below is no "
diff --git a/layout/style/nsRuleNode.h b/layout/style/nsRuleNode.h
index 1057e568e8d9..b5e9a97913ad 100644
--- a/layout/style/nsRuleNode.h
+++ b/layout/style/nsRuleNode.h
@@ -193,6 +193,7 @@ public:
     MOZ_ASSERT(!(mConditionalBits & GetBitForSID(aSID)),
                "rule node should not have unconditional and conditional style "
                "data for a given struct");
+    mConditionalBits &= ~GetBitForSID(aSID);
     mEntries[aSID] = aStyleStruct;
   }
 
@@ -200,13 +201,17 @@ public:
                     nsPresContext* aPresContext,
                     void* aStyleStruct,
                     const mozilla::RuleNodeCacheConditions& aConditions) {
-    MOZ_ASSERT((mConditionalBits & GetBitForSID(aSID)) ||
-               !mEntries[aSID],
-               "rule node should not have unconditional and conditional style "
-               "data for a given struct");
+    if (!(mConditionalBits & GetBitForSID(aSID))) {
+      MOZ_ASSERT(!mEntries[aSID],
+                 "rule node should not have unconditional and conditional "
+                 "style data for a given struct");
+      mEntries[aSID] = nullptr;
+    }
+
     MOZ_ASSERT(aConditions.CacheableWithDependencies(),
                "don't call SetStyleData with a cache key that has no "
                "conditions or is uncacheable");
+
 #ifdef DEBUG
     for (Entry* e = static_cast<Entry*>(mEntries[aSID]); e; e = e->mNext) {
       NS_WARNING_ASSERTION(e->mConditions != aConditions,