Restrict empty-frame cache entries to their parent

Remove the parser's global $mTplExpandCache, and replace it with an
alternative that is separated by parent frame. This allows the integrity
of the empty-frame expansion cache to be maintained while also allowing
parent frame access.

A page with 3 copies of 
http://ja.wikipedia.org/wiki/%E4%B8%AD%E5%A4%AE%E7%B7%9A_(%E9%9F%93%E5%9B%BD) 
has the following statistics: Without this change, there are 4625 cache hits
on this page, and a sample of 3 parses took 16.6, 16.9, and 16.8 seconds.
With this change, there are 2588 cache hits, and a sample of 3 parses took
16.7, 16.7, and 17.0 seconds.

Change-Id: I621e9075e0f136ac188a4d2f53418b7cc957408d

includes/parser/Parser.php

@@ -167,7 +167,6 @@ class Parser {
 	var $mLinkID;
 	var $mIncludeSizes, $mPPNodeCount, $mGeneratedPPNodeCount, $mHighestExpansionDepth;
 	var $mDefaultSort;
-	var $mTplExpandCache; # empty-frame expansion cache
 	var $mTplRedirCache, $mTplDomCache, $mHeadings, $mDoubleUnderscores;
 	var $mExpensiveFunctionCount; # number of expensive parser function calls
 	var $mShowToc, $mForceTocPosition;
@@ -321,7 +320,7 @@ class Parser {
 		$this->mStripState = new StripState( $this->mUniqPrefix );
 
 		# Clear these on every parse, bug 4549
-		$this->mTplExpandCache = $this->mTplRedirCache = $this->mTplDomCache = array();
+		$this->mTplRedirCache = $this->mTplDomCache = array();
 
 		$this->mShowToc = true;
 		$this->mForceTocPosition = false;
@@ -3562,12 +3561,7 @@ class Parser {
 				$text = $newFrame->expand( $text, PPFrame::RECOVER_ORIG );
 			} elseif ( $titleText !== false && $newFrame->isEmpty() ) {
 				# Expansion is eligible for the empty-frame cache
-				if ( isset( $this->mTplExpandCache[$titleText] ) ) {
-					$text = $this->mTplExpandCache[$titleText];
-				} else {
-					$text = $newFrame->expand( $text );
-					$this->mTplExpandCache[$titleText] = $text;
-				}
+				$text = $newFrame->cachedExpand( $titleText, $text );
 			} else {
 				# Uncached expansion
 				$text = $newFrame->expand( $text );

includes/parser/Preprocessor.php

@@ -94,6 +94,11 @@ interface PPFrame {
 	 */
 	function newChild( $args = false, $title = false, $indexOffset = 0 );
 
+	/**
+	 * Expand a document tree node, caching the result on its parent with the given key
+	 */
+	function cachedExpand( $key, $root, $flags = 0 );
+
 	/**
 	 * Expand a document tree node
 	 */

includes/parser/Preprocessor_DOM.php

@@ -983,6 +983,11 @@ class PPFrame_DOM implements PPFrame {
 	 */
 	var $depth;
 
+	/**
+	 * @var array
+	 */
+	protected $childExpansionCache;
+
 	/**
 	 * Construct a new preprocessor frame.
 	 * @param Preprocessor $preprocessor The parent preprocessor
@@ -994,6 +999,7 @@ class PPFrame_DOM implements PPFrame {
 		$this->titleCache = array( $this->title ? $this->title->getPrefixedDBkey() : false );
 		$this->loopCheckHash = array();
 		$this->depth = 0;
+		$this->childExpansionCache = array();
 	}
 
 	/**
@@ -1043,6 +1049,18 @@ class PPFrame_DOM implements PPFrame {
 		return new PPTemplateFrame_DOM( $this->preprocessor, $this, $numberedArgs, $namedArgs, $title );
 	}
 
+	/**
+	 * @throws MWException
+	 * @param string|int $key
+	 * @param string|PPNode_DOM|DOMDocument $root
+	 * @param int $flags
+	 * @return string
+	 */
+	function cachedExpand( $key, $root, $flags = 0 ) {
+		// we don't have a parent, so we don't have a cache
+		return $this->expand( $root, $flags );
+	}
+
 	/**
 	 * @throws MWException
 	 * @param string|PPNode_DOM|DOMDocument $root
@@ -1526,6 +1544,20 @@ class PPTemplateFrame_DOM extends PPFrame_DOM {
 		return $s;
 	}
 
+	/**
+	 * @throws MWException
+	 * @param string|int $key
+	 * @param string|PPNode_DOM|DOMDocument $root
+	 * @param int $flags
+	 * @return string
+	 */
+	function cachedExpand( $key, $root, $flags = 0 ) {
+		if ( !isset( $this->parent->childExpansionCache[$key] ) ) {
+			$this->parent->childExpansionCache[$key] = $this->expand( $root, $flags );
+		}
+		return $this->parent->childExpansionCache[$key];
+	}
+
 	/**
 	 * Returns true if there are no arguments in this frame
 	 *

includes/parser/Preprocessor_Hash.php

@@ -919,6 +919,11 @@ class PPFrame_Hash implements PPFrame {
 	 */
 	var $depth;
 
+	/**
+	 * @var array
+	 */
+	protected $childExpansionCache;
+
 	/**
 	 * Construct a new preprocessor frame.
 	 * @param Preprocessor $preprocessor The parent preprocessor
@@ -930,6 +935,7 @@ class PPFrame_Hash implements PPFrame {
 		$this->titleCache = array( $this->title ? $this->title->getPrefixedDBkey() : false );
 		$this->loopCheckHash = array();
 		$this->depth = 0;
+		$this->childExpansionCache = array();
 	}
 
 	/**
@@ -972,6 +978,18 @@ class PPFrame_Hash implements PPFrame {
 		return new PPTemplateFrame_Hash( $this->preprocessor, $this, $numberedArgs, $namedArgs, $title );
 	}
 
+	/**
+	 * @throws MWException
+	 * @param string|int $key
+	 * @param string|PPNode_Hash|DOMDocument $root
+	 * @param int $flags
+	 * @return string
+	 */
+	function cachedExpand( $key, $root, $flags = 0 ) {
+		// we don't have a parent, so we don't have a cache
+		return $this->expand( $root, $flags );
+	}
+
 	/**
 	 * @throws MWException
 	 * @param string|PPNode$root
@@ -1426,6 +1444,20 @@ class PPTemplateFrame_Hash extends PPFrame_Hash {
 		return $s;
 	}
 
+	/**
+	 * @throws MWException
+	 * @param string|int $key
+	 * @param string|PPNode_Hash|DOMDocument $root
+	 * @param int $flags
+	 * @return string
+	 */
+	function cachedExpand( $key, $root, $flags = 0 ) {
+		if ( !isset( $this->parent->childExpansionCache[$key] ) ) {
+			$this->parent->childExpansionCache[$key] = $this->expand( $root, $flags );
+		}
+		return $this->parent->childExpansionCache[$key];
+	}
+
 	/**
 	 * Returns true if there are no arguments in this frame
 	 *