[RTC] Fix performance regression on post save

packages/blocks/src/api/serializer.js

@@ -396,28 +396,43 @@ export function serializeBlock( block, { isInnerBlocks = false } = {} ) {
 	return getCommentDelimitedContent( blockName, saveAttributes, saveContent );
 }
 
-export function __unstableSerializeAndClean( blocks ) {
-	// A single unmodified default block is assumed to
-	// be equivalent to an empty post.
-	if ( blocks.length === 1 && isUnmodifiedDefaultBlock( blocks[ 0 ] ) ) {
-		blocks = [];
-	}
+export const __unstableSerializeAndClean = ( () => {
+	const cache = new WeakMap();
 
-	let content = serialize( blocks );
+	return ( blocks ) => {
+		const cached = cache.get( blocks );
+		if ( cached !== undefined ) {
+			return cached;
+		}
 
-	// For compatibility, treat a post consisting of a
-	// single freeform block as legacy content and apply
-	// pre-block-editor removep'd content formatting.
-	if (
-		blocks.length === 1 &&
-		blocks[ 0 ].name === getFreeformContentHandlerName() &&
-		blocks[ 0 ].name === 'core/freeform'
-	) {
-		content = removep( content );
-	}
+		let effectiveBlocks = blocks;
 
-	return content;
-}
+		// A single unmodified default block is assumed to
+		// be equivalent to an empty post.
+		if (
+			effectiveBlocks.length === 1 &&
+			isUnmodifiedDefaultBlock( effectiveBlocks[ 0 ] )
+		) {
+			effectiveBlocks = [];
+		}
+
+		let content = serialize( effectiveBlocks );
+
+		// For compatibility, treat a post consisting of a
+		// single freeform block as legacy content and apply
+		// pre-block-editor removep'd content formatting.
+		if (
+			effectiveBlocks.length === 1 &&
+			effectiveBlocks[ 0 ].name === getFreeformContentHandlerName() &&
+			effectiveBlocks[ 0 ].name === 'core/freeform'
+		) {
+			content = removep( content );
+		}
+
+		cache.set( blocks, content );
+		return content;
+	};
+} )();
 
 /**
  * Takes a block or set of blocks and returns the serialized post content.

packages/core-data/src/utils/crdt.ts

@@ -342,8 +342,6 @@ export function getPostChangesFromCRDTDoc(
 						);
 					}
 
-					// The consumers of blocks have memoization that renders optimization
-					// here unnecessary.
 					return true;
 				}