1 files changed, 113 insertions, 0 deletions
diff --git a/js/src/jsapi-tests/testDeduplication.cpp b/js/src/jsapi-tests/testDeduplication.cpp
new file mode 100644
index 0000000000..6e6ded6b71
--- /dev/null
+++ b/js/src/jsapi-tests/testDeduplication.cpp
@@ -0,0 +1,113 @@
+/* -*- 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 <string.h>
+
+#include "gc/GC.h"
+
+#include "js/RootingAPI.h"
+#include "js/StableStringChars.h"
+#include "js/String.h"  // JS::StringToLinearString
+
+#include "jsapi-tests/tests.h"
+
+#include "vm/JSContext.h"
+#include "vm/StringType.h"
+
+#include "vm/JSContext-inl.h"
+
+static bool SameChars(JSContext* cx, JSString* str1, JSString* str2,
+                      size_t offset) {
+  JS::AutoCheckCannotGC nogc(cx);
+
+  const JS::Latin1Char* chars1 =
+      JS::StringToLinearString(cx, str1)->latin1Chars(nogc);
+  const JS::Latin1Char* chars2 =
+      JS::StringToLinearString(cx, str2)->latin1Chars(nogc);
+
+  return chars1 == chars2 + offset;
+}
+
+BEGIN_TEST(testDeduplication_ASSC) {
+  // Test with a long enough string to avoid inline chars allocation.
+  const char text[] =
+      "Andthebeastshallcomeforthsurroundedbyaroilingcloudofvengeance."
+      "Thehouseoftheunbelieversshallberazedandtheyshallbescorchedtoth"
+      "eearth.Theirtagsshallblinkuntiltheendofdays.";
+
+  // Create a string to deduplicate later strings to.
+  JS::RootedString original(cx);
+  JS::RootedString str(cx);
+  JS::RootedString dep(cx);
+  JS::RootedString depdep(cx);
+  JS::RootedString str2(cx);
+  JS::RootedString dep2(cx);
+  JS::RootedString depdep2(cx);
+
+  {
+    // This test checks the behavior when GC is performed after allocating
+    // all the following strings.
+    // GC shouldn't happen in between them, even in compacting jobs.
+    js::gc::AutoSuppressGC suppress(cx);
+
+    original = JS_NewStringCopyZ(cx, text);
+    CHECK(original);
+
+    // Create a chain of dependent strings, with a base string whose contents
+    // match `original`'s.
+    str = JS_NewStringCopyZ(cx, text);
+    CHECK(str);
+
+    dep = JS_NewDependentString(cx, str, 10, 100);
+    CHECK(dep);
+
+    depdep = JS_NewDependentString(cx, dep, 10, 80);
+    CHECK(depdep);
+
+    // Repeat. This one will not be prevented from deduplication.
+    str2 = JS_NewStringCopyZ(cx, text);
+    CHECK(str2);
+
+    dep2 = JS_NewDependentString(cx, str2, 10, 100);
+    CHECK(dep2);
+
+    depdep2 = JS_NewDependentString(cx, dep2, 10, 80);
+    CHECK(depdep2);
+  }
+
+  // Initializing an AutoStableStringChars with `depdep` should prevent the
+  // owner of its chars (`str`) from deduplication.
+  JS::AutoStableStringChars stable(cx);
+  CHECK(stable.init(cx, depdep));
+
+  const JS::Latin1Char* chars = stable.latin1Chars();
+  CHECK(memcmp(chars, text + 20, 80 * sizeof(JS::Latin1Char)) == 0);
+
+  // `depdep` should share chars with `str` but not with `original`.
+  CHECK(SameChars(cx, depdep, str, 20));
+  CHECK(!SameChars(cx, depdep, original, 20));
+
+  // Same for `depdep2`.
+  CHECK(SameChars(cx, depdep2, str2, 20));
+  CHECK(!SameChars(cx, depdep2, original, 20));
+
+  // Do a minor GC that will deduplicate `str2` to `original`, and would have
+  // deduplicated `str` as well if it weren't prevented by the
+  // AutoStableStringChars.
+  cx->minorGC(JS::GCReason::API);
+
+  // `depdep` should still share chars with `str` but not with `original`.
+  CHECK(SameChars(cx, depdep, str, 20));
+  CHECK(!SameChars(cx, depdep, original, 20));
+
+  // `depdep2` should now share chars with both `str` and `original`.
+  CHECK(SameChars(cx, depdep2, str2, 20));
+  CHECK(SameChars(cx, depdep2, original, 20));
+
+  return true;
+}
+END_TEST(testDeduplication_ASSC)