Bug 711266 - JSRope::flatten needs unconditional post barriers; r=billm

For incremental barriers we check if compartment()->needsBarrier to defer the
cost when we are not in a GC cycle.  We cannot do this for cross-generation
barriers.  We need to remove the checks on the post barriers and rename the enum
to something  more specific.

js/src/vm/String-inl.h

@@ -93,6 +93,8 @@ JSRope::init(JSString *left, JSString *right, size_t length)
     d.lengthAndFlags = buildLengthAndFlags(length, ROPE_BIT);
     d.u1.left = left;
     d.s.u2.right = right;
+    JSString::writeBarrierPost(d.u1.left, &d.u1.left);
+    JSString::writeBarrierPost(d.s.u2.right, &d.s.u2.right);
 }
 
 JS_ALWAYS_INLINE JSRope *
@@ -113,6 +115,7 @@ JSDependentString::init(JSLinearString *base, const jschar *chars, size_t length
     d.lengthAndFlags = buildLengthAndFlags(length, DEPENDENT_BIT);
     d.u1.chars = chars;
     d.s.u2.base = base;
+    JSString::writeBarrierPost(d.s.u2.base, &d.s.u2.base);
 }
 
 JS_ALWAYS_INLINE JSDependentString *

js/src/vm/String.cpp

@@ -187,7 +187,7 @@ JSRope::flattenInternal(JSContext *maybecx)
         JSExtensibleString &left = this->leftChild()->asExtensible();
         size_t capacity = left.capacity();
         if (capacity >= wholeLength) {
-            if (b == WithBarrier) {
+            if (b == WithIncrementalBarrier) {
                 JSString::writeBarrierPre(d.u1.left);
                 JSString::writeBarrierPre(d.s.u2.right);
             }
@@ -198,8 +198,7 @@ JSRope::flattenInternal(JSContext *maybecx)
             pos = wholeChars + (bits >> LENGTH_SHIFT);
             left.d.lengthAndFlags = bits ^ (EXTENSIBLE_FLAGS | DEPENDENT_BIT);
             left.d.s.u2.base = (JSLinearString *)this;  /* will be true on exit */
-            if (b == WithBarrier)
+            JSString::writeBarrierPost(left.d.s.u2.base, &left.d.s.u2.base);
-                JSString::writeBarrierPost(this, &left.d.s.u2.base);
             goto visit_right_child;
         }
     }
@@ -209,7 +208,7 @@ JSRope::flattenInternal(JSContext *maybecx)
 
     pos = wholeChars;
     first_visit_node: {
-        if (b == WithBarrier) {
+        if (b == WithIncrementalBarrier) {
             JSString::writeBarrierPre(str->d.u1.left);
             JSString::writeBarrierPre(str->d.s.u2.right);
         }
@@ -250,8 +249,7 @@ JSRope::flattenInternal(JSContext *maybecx)
         size_t progress = str->d.lengthAndFlags;
         str->d.lengthAndFlags = buildLengthAndFlags(pos - str->d.u1.chars, DEPENDENT_BIT);
         str->d.s.u2.base = (JSLinearString *)this;       /* will be true on exit */
-        if (b == WithBarrier)
+        JSString::writeBarrierPost(str->d.s.u2.base, &str->d.s.u2.base);
-            JSString::writeBarrierPost(this, &str->d.s.u2.base);
         str = str->d.s.u3.parent;
         if (progress == 0x200)
             goto visit_right_child;
@@ -265,7 +263,7 @@ JSRope::flatten(JSContext *maybecx)
 {
 #if JSGC_INCREMENTAL
     if (compartment()->needsBarrier())
-        return flattenInternal<WithBarrier>(maybecx);
+        return flattenInternal<WithIncrementalBarrier>(maybecx);
     else
         return flattenInternal<NoBarrier>(maybecx);
 #else

js/src/vm/String.h

@@ -426,7 +426,7 @@ class JSString : public js::gc::Cell
 
 class JSRope : public JSString
 {
-    enum UsingBarrier { WithBarrier, NoBarrier };
+    enum UsingBarrier { WithIncrementalBarrier, NoBarrier };
     template<UsingBarrier b>
     JSFlatString *flattenInternal(JSContext *cx);