From fbc9537952622645a4a45ce28ec90956c85922f9 Mon Sep 17 00:00:00 2001
From: Vikram Subramanian <vikram.subramanian@gmail.com>
Date: Wed, 4 Oct 2017 01:53:39 -0700
Subject: [PATCH] perf(compiler): fix perf issue in loading aot summaries in
 jit compiler

The current `flattenSummaries` function re-process the same NgModule
summary even if it has been processed before. Certain modules like
CommonModule are repeated multiple times in the module tree and it is
expanded out every time.

This was making unit tests using AOT summaries really slow. This will
also slow down JIT bootstrap applications that load AOT summaries for
component libraries.

The fix is to remember which summaries were seen before and not to
process them again.
---
 packages/compiler/src/jit/compiler.ts | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/packages/compiler/src/jit/compiler.ts b/packages/compiler/src/jit/compiler.ts
index 409b3a49b1..18ddbe5686 100644
--- a/packages/compiler/src/jit/compiler.ts
+++ b/packages/compiler/src/jit/compiler.ts
@@ -335,14 +335,22 @@ function assertComponent(meta: CompileDirectiveMetadata) {
   }
 }
 
-function flattenSummaries(fn: () => any[], out: CompileTypeSummary[] = []): CompileTypeSummary[] {
-  fn().forEach((entry) => {
+function flattenSummaries(
+    fn: () => any[], out: CompileTypeSummary[] = [],
+    seen = new Set<() => any[]>()): CompileTypeSummary[] {
+  if (seen.has(fn)) {
+    return out;
+  }
+  seen.add(fn);
+  const summaries = fn();
+  for (let i = 0; i < summaries.length; i++) {
+    const entry = summaries[i];
     if (typeof entry === 'function') {
-      flattenSummaries(entry, out);
+      flattenSummaries(entry, out, seen);
     } else {
       out.push(entry);
     }
-  });
+  }
   return out;
 }