--- a/js/src/jit/MIR.cpp
+++ b/js/src/jit/MIR.cpp
@@ -321,16 +321,28 @@ MTest::foldsTo(TempAllocator &alloc)
         if (opop->isNot())
             return MTest::New(alloc, opop->toNot()->input(), ifTrue(), ifFalse());
         return MTest::New(alloc, op->toNot()->input(), ifFalse(), ifTrue());
     }
 
     if (op->isConstant())
         return MGoto::New(alloc, op->toConstant()->valueToBoolean() ? ifTrue() : ifFalse());
 
+    switch (op->type()) {
+      case MIRType_Undefined:
+      case MIRType_Null:
+        return MGoto::New(alloc, ifFalse());
+      case MIRType_Object:
+        if (!operandMightEmulateUndefined())
+            return MGoto::New(alloc, ifTrue());
+        break;
+      default:
+        break;
+    }
+
     return this;
 }
 
 void
 MTest::filtersUndefinedOrNull(bool trueBranch, MDefinition **subject, bool *filtersUndefined,
                               bool *filtersNull)
 {
     MDefinition *ins = getOperand(0);
@@ -3545,16 +3557,30 @@ MBoundsCheck::foldsTo(TempAllocator &all
        if (idx + uint32_t(minimum()) < len && idx + uint32_t(maximum()) < len)
            return index();
     }
 
     return this;
 }
 
 MDefinition *
+MTableSwitch::foldsTo(TempAllocator &alloc)
+{
+    MDefinition *op = getOperand(0);
+
+    // If we only have one successor, convert to a plain goto to the only
+    // successor. TableSwitch indices are numeric; other types will always go to
+    // the only successor.
+    if (numSuccessors() == 1 || (op->type() != MIRType_Value && !IsNumberType(op->type())))
+        return MGoto::New(alloc, getDefault());
+
+    return this;
+}
+
+MDefinition *
 MArrayJoin::foldsTo(TempAllocator &alloc) {
     // :TODO: Enable this optimization after fixing Bug 977966 test cases.
     return this;
 
     MDefinition *arr = array();
 
     if (!arr->isStringSplit())
         return this;

--- a/js/src/jit/MIR.h
+++ b/js/src/jit/MIR.h
@@ -1880,16 +1880,18 @@ class MTableSwitch MOZ_FINAL
     void replaceOperand(size_t index, MDefinition *operand) MOZ_FINAL MOZ_OVERRIDE {
         JS_ASSERT(index == 0);
         operand_.replaceProducer(operand);
     }
 
     TypePolicy *typePolicy() {
         return this;
     }
+
+    MDefinition *foldsTo(TempAllocator &alloc);
 };
 
 template <size_t Arity, size_t Successors>
 class MAryControlInstruction : public MControlInstruction
 {
     mozilla::Array<MUse, Arity> operands_;
     mozilla::Array<MBasicBlock *, Successors> successors_;