Bug 807535 - Avoid toggling Ion write barrier too often. r=sstangl, a=bajaj

js/src/jscompartment.cpp

@@ -48,6 +48,7 @@ JSCompartment::JSCompartment(JSRuntime *rt)
     gcStoreBuffer(&gcNursery),
 #endif
     needsBarrier_(false),
+    ionUsingBarriers_(false),
     gcScheduled(false),
     gcState(NoGC),
     gcPreserveCode(false),
@@ -131,7 +132,7 @@ JSCompartment::init(JSContext *cx)
 }
 
 void
-JSCompartment::setNeedsBarrier(bool needs)
+JSCompartment::setNeedsBarrier(bool needs, ShouldUpdateIon updateIon)
 {
 #ifdef JS_METHODJIT
     /* ClearAllFrames calls compileBarriers() and needs the old value. */
@@ -141,8 +142,10 @@ JSCompartment::setNeedsBarrier(bool needs)
 #endif
 
 #ifdef JS_ION
-    if (needsBarrier_ != needs)
+    if (updateIon == UpdateIon && needs != ionUsingBarriers_) {
         ion::ToggleBarriers(this, needs);
+        ionUsingBarriers_ = needs;
+    }
 #endif
 
     needsBarrier_ = needs;

js/src/jscompartment.h

@@ -155,6 +155,7 @@ struct JSCompartment
 
   private:
     bool                         needsBarrier_;
+    bool                         ionUsingBarriers_;
   public:
 
     bool needsBarrier() const {
@@ -169,7 +170,12 @@ struct JSCompartment
         return compileBarriers(needsBarrier());
     }
 
-    void setNeedsBarrier(bool needs);
+    enum ShouldUpdateIon {
+        DontUpdateIon,
+        UpdateIon
+    };
+
+    void setNeedsBarrier(bool needs, ShouldUpdateIon updateIon);
 
     static size_t OffsetOfNeedsBarrier() {
         return offsetof(JSCompartment, needsBarrier_);

js/src/jsgc.cpp

@@ -4162,7 +4162,7 @@ ResetIncrementalGC(JSRuntime *rt, const char *reason)
         AutoCopyFreeListToArenas copy(rt);
         for (GCCompartmentsIter c(rt); !c.done(); c.next()) {
             if (c->isGCMarking()) {
-                c->setNeedsBarrier(false);
+                c->setNeedsBarrier(false, JSCompartment::DontUpdateIon);
                 c->setGCState(JSCompartment::NoGC);
                 wasMarking = true;
             }
@@ -4220,10 +4220,15 @@ AutoGCSlice::AutoGCSlice(JSRuntime *rt)
     rt->stackSpace.markActiveCompartments();
 
     for (GCCompartmentsIter c(rt); !c.done(); c.next()) {
-        /* Clear this early so we don't do any write barriers during GC. */
+        /*
+         * Clear needsBarrier early so we don't do any write barriers during
+         * GC. We don't need to update the Ion barriers (which is expensive)
+         * because Ion code doesn't run during GC. If need be, we'll update the
+         * Ion barriers in ~AutoGCSlice.
+         */
         if (c->isGCMarking()) {
             JS_ASSERT(c->needsBarrier());
-            c->setNeedsBarrier(false);
+            c->setNeedsBarrier(false, JSCompartment::DontUpdateIon);
         } else {
             JS_ASSERT(!c->needsBarrier());
         }
@@ -4234,11 +4239,11 @@ AutoGCSlice::~AutoGCSlice()
 {
     for (GCCompartmentsIter c(runtime); !c.done(); c.next()) {
         if (c->isGCMarking()) {
-            c->setNeedsBarrier(true);
+            c->setNeedsBarrier(true, JSCompartment::UpdateIon);
             c->arenas.prepareForIncrementalGC(runtime);
         } else {
             JS_ASSERT(c->isGCSweeping());
-            c->setNeedsBarrier(false);
+            c->setNeedsBarrier(false, JSCompartment::UpdateIon);
         }
     }
 }
@@ -5351,7 +5356,7 @@ StartVerifyPreBarriers(JSRuntime *rt)
     rt->gcMarker.start(rt);
     for (CompartmentsIter c(rt); !c.done(); c.next()) {
         PurgeJITCaches(c);
-        c->setNeedsBarrier(true);
+        c->setNeedsBarrier(true, JSCompartment::UpdateIon);
         c->arenas.purge();
     }
 
@@ -5434,7 +5439,7 @@ EndVerifyPreBarriers(JSRuntime *rt)
             compartmentCreated = true;
 
         PurgeJITCaches(c);
-        c->setNeedsBarrier(false);
+        c->setNeedsBarrier(false, JSCompartment::UpdateIon);
     }
 
     /*