Bug 1062869 part 6 - Handle early execution of recover instructions. r=h4writer

js/src/jit/CompileInfo.h

@@ -444,6 +444,16 @@ class CompileInfo
     // would have to be executed and that they cannot be removed even if they
     // are unused.
     bool isObservableSlot(uint32_t slot) const {
+        if (isObservableFrameSlot(slot))
+            return true;
+
+        if (isObservableArgumentSlot(slot))
+            return true;
+
+        return false;
+    }
+
+    bool isObservableFrameSlot(uint32_t slot) const {
         if (!funMaybeLazy())
             return false;
 
@@ -458,6 +468,13 @@ class CompileInfo
         if (hasArguments() && (slot == scopeChainSlot() || slot == argsObjSlot()))
             return true;
 
+        return false;
+    }
+
+    bool isObservableArgumentSlot(uint32_t slot) const {
+        if (!funMaybeLazy())
+            return false;
+
         // Function.arguments can be used to access all arguments in non-strict
         // scripts, so we can't optimize out any arguments.
         if ((hasArguments() || !script()->strict()) &&
@@ -469,6 +486,19 @@ class CompileInfo
         return false;
     }
 
+    // Returns true if a slot can be recovered before or during a bailout.  A
+    // definition which can be observed and recovered, implies that this
+    // definition can be optimized away as long as we can compute its values.
+    bool isRecoverableOperand(uint32_t slot) const {
+        if (isObservableFrameSlot(slot))
+            return false;
+
+        if (needsArgsObj() && isObservableArgumentSlot(slot))
+            return false;
+
+        return true;
+    }
+
   private:
     unsigned nimplicit_;
     unsigned nargs_;

js/src/jit/IonFrames.cpp

@@ -1772,6 +1772,50 @@ SnapshotIterator::skipInstruction()
     nextInstruction();
 }
 
+bool
+SnapshotIterator::initInstructionResults(MaybeReadFallback &fallback)
+{
+    MOZ_ASSERT(fallback.canRecoverResults());
+    JSContext *cx = fallback.maybeCx;
+
+    // If there is only one resume point in the list of instructions, then there
+    // is no instruction to recover, and thus no need to register any results.
+    MOZ_ASSERT(recover_.numInstructionsRead() == 1);
+    if (recover_.numInstructions() == 1)
+        return true;
+
+    IonJSFrameLayout *fp = fallback.frame->jsFrame();
+    RInstructionResults *results = fallback.activation->maybeIonFrameRecovery(fp);
+    if (!results) {
+        // We do not have the result yet, which means that an observable stack
+        // slot is requested.  As we do not want to bailout every time for the
+        // same reason, we need to recompile without optimizing away the
+        // observable stack slots.  The script would later be recompiled to have
+        // support for Argument objects.
+        if (!ionScript_->invalidate(cx, /* resetUses = */ false, "Observe recovered instruction."))
+            return false;
+
+        // Start a new snapshot at the beginning of the JitFrameIterator.  This
+        // SnapshotIterator is used for evaluating the content of all recover
+        // instructions.  The result is then saved on the JitActivation.
+        SnapshotIterator s(*fallback.frame);
+        RInstructionResults tmp;
+        if (!s.initInstructionResults(cx, &tmp))
+            return false;
+
+        // Register the list of result on the activation.
+        if (!fallback.activation->registerIonFrameRecovery(fallback.frame->jsFrame(),
+                                                           mozilla::Move(tmp)))
+            return false;
+
+        results = fallback.activation->maybeIonFrameRecovery(fp);
+    }
+
+    MOZ_ASSERT(results->isInitialized());
+    instructionResults_ = results;
+    return true;
+}
+
 bool
 SnapshotIterator::initInstructionResults(JSContext *cx, RInstructionResults *results)
 {

js/src/jit/JitFrameIterator.h

@@ -424,6 +424,7 @@ class SnapshotIterator
     // recover instructions. This vector should be registered before the
     // beginning of the iteration. This function is in charge of allocating
     // enough space for all instructions results, and return false iff it fails.
+    bool initInstructionResults(MaybeReadFallback &fallback);
     bool initInstructionResults(JSContext *cx, RInstructionResults *results);
 
     void storeInstructionResult(Value v);
@@ -458,8 +459,16 @@ class SnapshotIterator
         if (allocationReadable(a))
             return allocationValue(a);
 
-        if (fallback.canRecoverResults())
-            warnUnreadableAllocation();
+        if (fallback.canRecoverResults()) {
+            if (!initInstructionResults(fallback))
+                return fallback.unreadablePlaceholder;
+
+            if (allocationReadable(a))
+                return allocationValue(a);
+
+            MOZ_ASSERT_UNREACHABLE("All allocations should be readable.");
+        }
+
         return fallback.unreadablePlaceholder;
     }
 

js/src/jit/MIR.cpp

@@ -501,7 +501,7 @@ MDefinition::hasLiveDefUses() const
                 return true;
         } else {
             MOZ_ASSERT(ins->isResumePoint());
-            if (ins->toResumePoint()->isObservableOperand(*i))
+            if (!ins->toResumePoint()->isRecoverableOperand(*i))
                 return true;
         }
     }
@@ -2708,6 +2708,12 @@ MResumePoint::isObservableOperand(size_t index) const
     return block()->info().isObservableSlot(index);
 }
 
+bool
+MResumePoint::isRecoverableOperand(MUse *u) const
+{
+    return block()->info().isRecoverableOperand(indexOf(u));
+}
+
 MDefinition *
 MToInt32::foldsTo(TempAllocator &alloc)
 {

js/src/jit/MIR.h

@@ -10796,6 +10796,7 @@ class MResumePoint MOZ_FINAL :
 
     bool isObservableOperand(MUse *u) const;
     bool isObservableOperand(size_t index) const;
+    bool isRecoverableOperand(MUse *u) const;
 
     MDefinition *getOperand(size_t index) const {
         return operands_[index].producer();

js/src/jit/ScalarReplacement.cpp

@@ -146,8 +146,8 @@ IsObjectEscaped(MInstruction *ins)
         MNode *consumer = (*i)->consumer();
         if (!consumer->isDefinition()) {
             // Cannot optimize if it is observable from fun.arguments or others.
-            if (consumer->toResumePoint()->isObservableOperand(*i)) {
-                JitSpewDef(JitSpew_Escape, "Object is observable\n", ins);
+            if (!consumer->toResumePoint()->isRecoverableOperand(*i)) {
+                JitSpewDef(JitSpew_Escape, "Observable object cannot be recovered\n", ins);
                 return true;
             }
             continue;
@@ -525,8 +525,8 @@ IsArrayEscaped(MInstruction *ins)
         MNode *consumer = (*i)->consumer();
         if (!consumer->isDefinition()) {
             // Cannot optimize if it is observable from fun.arguments or others.
-            if (consumer->toResumePoint()->isObservableOperand(*i)) {
-                JitSpewDef(JitSpew_Escape, "Array is observable\n", ins);
+            if (!consumer->toResumePoint()->isRecoverableOperand(*i)) {
+                JitSpewDef(JitSpew_Escape, "Observable array cannot be recovered\n", ins);
                 return true;
             }
             continue;