Bug 1655203 - Add tests for AutoStableStringChars and deduplication r=jonco

Differential Revision: https://phabricator.services.mozilla.com/D84872

js/src/jit-test/tests/gc/dedupe-02.js

@@ -0,0 +1,39 @@
+// AutoStableStringChars needs to prevent the owner of its chars from being
+// deduplicated, even if they are held by a different string.
+
+gczeal(0);
+
+function makeExtensibleStrFrom(str) {
+  var left = str.substr(0, str.length/2);
+  var right = str.substr(str.length/2, str.length);
+  var ropeStr = left + right;
+  return ensureLinearString(ropeStr);
+}
+
+// Make a string to deduplicate to.
+var original = makeExtensibleStrFrom('{ "phbbbbbbbbbbbbbbttt!!!!??": [1] }\n\n');
+
+// Construct D2 -> D1 -> base
+var D2 = makeExtensibleStrFrom('{ "phbbbbbbbbbbbbbbttt!!!!??": [1] }');
+var D1 = newRope(D2, '\n', {nursery: true});
+ensureLinearString(D1);
+var base = newRope(D1, '\n', {nursery: true});
+ensureLinearString(base);
+
+// Make an AutoStableStringChars(D2) and do a minor GC within it. (This will do
+// a major GC, but it'll start out with a minor GC.) `base` would get
+// deduplicated to `original`, if it weren't for AutoStableStringChars marking
+// all of D2, D1, and base non-deduplicatable.
+
+// The first time JSON.parse runs, it will create several (14 in my test) GC
+// things before getting to the point where it does an allocation while holding
+// the chars pointer. Get them out of the way now.
+JSON.parse(D2);
+
+// Cause a minor GC to happen during JSON.parse after AutoStableStringChars
+// gives up its pointer.
+schedulegc(1);
+JSON.parse(D2);
+
+// Access `D2` to verify that it is not using the deduplicated chars.
+print(D2);

js/src/jit-test/tests/gc/dedupe.js

@@ -0,0 +1,44 @@
+function str(c) {
+    let s = c;
+    for (let i = 0; i < 30; i++)
+        s += c;
+    ensureLinearString(s);
+    return s;
+}
+
+function f() {
+  // Create some slots to write into.
+  const o = {owner: 'short1', s: 'short2'};
+
+  // Make a tenured rope.
+  const r1 = str("a") + str("b");
+  gc();
+
+  // Write the first instance of our duplicate string into one of the slots
+  // (`owner`). This will be scanned first, and entered into deDupSet when
+  // tenured.
+  o.owner = ensureLinearString(str("a") + str("b") + str("c"));
+
+  // Make another rope with identical contents, with a tenured subtree.
+  const r2 = r1 + str("c");
+
+  // Linearize the new rope, creating a new extensible string and a bunch of
+  // dependent strings replacing the rest of the rope nodes.
+  ensureLinearString(r2);
+
+  // Write the new rope into a slot, so that it will be scanned next during the
+  // minor GC during traceSlots().
+  o.s = r2;
+
+  // Do a nursery collection. o.owner will be tenured and inserted into
+  // deDupSet. Then o.s aka r2 will be tenured. If things work correctly, r2
+  // will be marked non-deduplicatable because it is the base of a tenured
+  // string r1. If not, it will be deduplicated to o.owner.
+  minorgc();
+
+  // Extract out that r1 child node. If its base was deduplicated, this will
+  // assert because its chars have been freed.
+  const s1 = r1.substr(0, 31);
+}
+
+f();

js/src/jsapi-tests/moz.build

@@ -28,6 +28,7 @@ UNIFIED_SOURCES += [
     'testCompileUtf8.cpp',
     'testDateToLocaleString.cpp',
     'testDebugger.cpp',
+    'testDeduplication.cpp',
     'testDeepFreeze.cpp',
     'testDefineGetterSetterNonEnumerable.cpp',
     'testDefineProperty.cpp',

js/src/jsapi-tests/testDeduplication.cpp

@@ -0,0 +1,97 @@
+/* -*- 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 "jsfriendapi.h"
+
+#include "js/RootingAPI.h"
+#include "js/StableStringChars.h"
+
+#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_NewStringCopyZ(cx, text));
+  CHECK(original);
+
+  // Create a chain of dependent strings, with a base string whose contents
+  // match `original`'s.
+  JS::RootedString str(cx, JS_NewStringCopyZ(cx, text));
+  CHECK(str);
+
+  JS::RootedString dep(cx, JS_NewDependentString(cx, str, 10, 100));
+  CHECK(str);
+
+  JS::RootedString depdep(cx, JS_NewDependentString(cx, dep, 10, 80));
+  CHECK(str);
+
+  // Repeat. This one will not be prevented from deduplication.
+  JS::RootedString str2(cx, JS_NewStringCopyZ(cx, text));
+  CHECK(str);
+
+  JS::RootedString dep2(cx, JS_NewDependentString(cx, str2, 10, 100));
+  CHECK(str);
+
+  JS::RootedString depdep2(cx, JS_NewDependentString(cx, dep2, 10, 80));
+  CHECK(str);
+
+  // 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)