diff --git a/js/src/jit/CodeGenerator.cpp b/js/src/jit/CodeGenerator.cpp
index 84e793a47092..b8db737d7c77 100644
--- a/js/src/jit/CodeGenerator.cpp
+++ b/js/src/jit/CodeGenerator.cpp
@@ -1474,6 +1474,21 @@ void CodeGenerator::testValueTruthy(const ValueOperand& value,
   masm.jump(ifTruthy);
 }
 
+void CodeGenerator::visitTestBIAndBranch(LTestBIAndBranch* lir) {
+  Label* ifTrueLabel = getJumpLabelForBranch(lir->ifTrue());
+  Label* ifFalseLabel = getJumpLabelForBranch(lir->ifFalse());
+  Register input = ToRegister(lir->input());
+
+  if (isNextBlock(lir->ifFalse()->lir())) {
+    masm.branchIfBigIntIsNonZero(input, ifTrueLabel);
+  } else if (isNextBlock(lir->ifTrue()->lir())) {
+    masm.branchIfBigIntIsZero(input, ifFalseLabel);
+  } else {
+    masm.branchIfBigIntIsZero(input, ifFalseLabel);
+    jumpToBlock(lir->ifTrue());
+  }
+}
+
 void CodeGenerator::visitTestOAndBranch(LTestOAndBranch* lir) {
   Label* truthy = getJumpLabelForBranch(lir->ifTruthy());
   Label* falsy = getJumpLabelForBranch(lir->ifFalsy());
@@ -10248,6 +10263,14 @@ void CodeGenerator::visitSetInitializedLength(LSetInitializedLength* lir) {
   SetLengthFromIndex(masm, lir->index(), initLength);
 }
 
+void CodeGenerator::visitNotBI(LNotBI* lir) {
+  Register input = ToRegister(lir->input());
+  Register output = ToRegister(lir->output());
+
+  masm.cmp32Set(Assembler::Equal, Address(input, BigInt::offsetOfLength()),
+                Imm32(0), output);
+}
+
 void CodeGenerator::visitNotO(LNotO* lir) {
   auto* ool = new (alloc()) OutOfLineTestObjectWithLabels();
   addOutOfLineCode(ool, lir->mir());
diff --git a/js/src/jit/Lowering.cpp b/js/src/jit/Lowering.cpp
index 32a371937da1..2da50166eb6d 100644
--- a/js/src/jit/Lowering.cpp
+++ b/js/src/jit/Lowering.cpp
@@ -571,10 +571,6 @@ void LIRGenerator::visitTest(MTest* test) {
   // TestPolicy).
   MOZ_ASSERT(opd->type() != MIRType::String);
 
-  // BigInt is boxed in type analysis.
-  MOZ_ASSERT(opd->type() != MIRType::BigInt,
-             "BigInt should be boxed by TestPolicy");
-
   // Testing a constant.
   if (MConstant* constant = opd->maybeConstantValue()) {
     bool b;
@@ -814,6 +810,9 @@ void LIRGenerator::visitTest(MTest* test) {
       add(new (alloc())
               LTestI64AndBranch(useInt64Register(opd), ifTrue, ifFalse));
       break;
+    case MIRType::BigInt:
+      add(new (alloc()) LTestBIAndBranch(useRegister(opd), ifTrue, ifFalse));
+      break;
     default:
       MOZ_CRASH("Bad type");
   }
@@ -3008,13 +3007,13 @@ void LIRGenerator::visitNot(MNot* ins) {
   // String is converted to length of string in the type analysis phase (see
   // TestPolicy).
   MOZ_ASSERT(op->type() != MIRType::String);
-  MOZ_ASSERT(op->type() != MIRType::BigInt,
-             "BigInt should be boxed by TestPolicy");
 
   // - boolean: x xor 1
   // - int32: LCompare(x, 0)
   // - double: LCompare(x, 0)
   // - null or undefined: true
+  // - symbol: false
+  // - bigint: LNotBI(x)
   // - object: false if it never emulates undefined, else LNotO(x)
   switch (op->type()) {
     case MIRType::Boolean: {
@@ -3042,6 +3041,9 @@ void LIRGenerator::visitNot(MNot* ins) {
     case MIRType::Symbol:
       define(new (alloc()) LInteger(0), ins);
       break;
+    case MIRType::BigInt:
+      define(new (alloc()) LNotBI(useRegisterAtStart(op)), ins);
+      break;
     case MIRType::Object:
       define(new (alloc()) LNotO(useRegister(op)), ins);
       break;
diff --git a/js/src/jit/TypePolicy.cpp b/js/src/jit/TypePolicy.cpp
index 5dc274c8c85f..384cf3bec828 100644
--- a/js/src/jit/TypePolicy.cpp
+++ b/js/src/jit/TypePolicy.cpp
@@ -279,6 +279,7 @@ bool TestPolicy::adjustInputs(TempAllocator& alloc, MInstruction* ins) const {
     case MIRType::Double:
     case MIRType::Float32:
     case MIRType::Symbol:
+    case MIRType::BigInt:
     case MIRType::Object:
       break;
 
@@ -290,8 +291,7 @@ bool TestPolicy::adjustInputs(TempAllocator& alloc, MInstruction* ins) const {
     }
 
     default:
-      ins->replaceOperand(0, BoxAt(alloc, ins, op));
-      break;
+      MOZ_CRASH("Unexpected MIRType.");
   }
   return true;
 }
diff --git a/js/src/jit/shared/LIR-shared.h b/js/src/jit/shared/LIR-shared.h
index d0200aff268f..af77e108f51f 100644
--- a/js/src/jit/shared/LIR-shared.h
+++ b/js/src/jit/shared/LIR-shared.h
@@ -1355,7 +1355,7 @@ class LTestI64AndBranch : public LControlInstructionHelper<2, INT64_PIECES, 0> {
   MBasicBlock* ifFalse() const { return getSuccessor(1); }
 };
 
-// Takes in either an integer or boolean input and tests it for truthiness.
+// Takes in a double input and tests it for truthiness.
 class LTestDAndBranch : public LControlInstructionHelper<2, 1, 0> {
  public:
   LIR_HEADER(TestDAndBranch)
@@ -1372,7 +1372,7 @@ class LTestDAndBranch : public LControlInstructionHelper<2, 1, 0> {
   MBasicBlock* ifFalse() const { return getSuccessor(1); }
 };
 
-// Takes in either an integer or boolean input and tests it for truthiness.
+// Takes in a float32 input and tests it for truthiness.
 class LTestFAndBranch : public LControlInstructionHelper<2, 1, 0> {
  public:
   LIR_HEADER(TestFAndBranch)
@@ -1389,6 +1389,23 @@ class LTestFAndBranch : public LControlInstructionHelper<2, 1, 0> {
   MBasicBlock* ifFalse() const { return getSuccessor(1); }
 };
 
+// Takes in a bigint input and tests it for truthiness.
+class LTestBIAndBranch : public LControlInstructionHelper<2, 1, 0> {
+ public:
+  LIR_HEADER(TestBIAndBranch)
+
+  LTestBIAndBranch(const LAllocation& in, MBasicBlock* ifTrue,
+                   MBasicBlock* ifFalse)
+      : LControlInstructionHelper(classOpcode) {
+    setOperand(0, in);
+    setSuccessor(0, ifTrue);
+    setSuccessor(1, ifFalse);
+  }
+
+  MBasicBlock* ifTrue() { return getSuccessor(0); }
+  MBasicBlock* ifFalse() { return getSuccessor(1); }
+};
+
 // Takes an object and tests it for truthiness.  An object is falsy iff it
 // emulates |undefined|; see js::EmulatesUndefined.
 class LTestOAndBranch : public LControlInstructionHelper<2, 1, 1> {
@@ -1884,6 +1901,18 @@ class LNotF : public LInstructionHelper<1, 1, 0> {
   MNot* mir() { return mir_->toNot(); }
 };
 
+// Not operation on a BigInt.
+class LNotBI : public LInstructionHelper<1, 1, 0> {
+ public:
+  LIR_HEADER(NotBI)
+
+  explicit LNotBI(const LAllocation& input) : LInstructionHelper(classOpcode) {
+    setOperand(0, input);
+  }
+
+  MNot* mir() { return mir_->toNot(); }
+};
+
 // Boolean complement operation on an object.
 class LNotO : public LInstructionHelper<1, 1, 0> {
  public: