diff --git a/include/swift/AST/Builtins.def b/include/swift/AST/Builtins.def
index f1b4b6b23e076..f0369e86c9635 100644
--- a/include/swift/AST/Builtins.def
+++ b/include/swift/AST/Builtins.def
@@ -175,6 +175,8 @@ BUILTIN_UNARY_OPERATION(FNeg, "fneg", "n", FloatOrVector)
 BUILTIN_UNARY_OPERATION(AssumeNonNegative, "assumeNonNegative", "n", Integer)
 // It only works on i1.
 BUILTIN_UNARY_OPERATION(AssumeTrue, "assume", "", Integer)
+// Converts poison/undef to an indeterminate but valid value.
+BUILTIN_UNARY_OPERATION(Freeze, "freeze", "n", IntegerOrVector)
 
 // Binary predicates have type (T,T) -> i1 or (T, T) -> Vector<i1> for scalars
 // and vectors, respectively.
diff --git a/lib/IRGen/GenBuiltin.cpp b/lib/IRGen/GenBuiltin.cpp
index cac9788268130..c34954d3acbba 100644
--- a/lib/IRGen/GenBuiltin.cpp
+++ b/lib/IRGen/GenBuiltin.cpp
@@ -637,6 +637,9 @@ void irgen::emitBuiltinCall(IRGenFunction &IGF, const BuiltinInfo &Builtin,
     // Don't generate any code for the builtin.
     return out.add(v);
   }
+  if (Builtin.ID == BuiltinValueKind::Freeze) {
+    return out.add(IGF.Builder.CreateFreeze(args.claimNext()));
+  }
   
   if (Builtin.ID == BuiltinValueKind::AllocRaw) {
     auto size = args.claimNext();
diff --git a/lib/SIL/IR/OperandOwnership.cpp b/lib/SIL/IR/OperandOwnership.cpp
index 9af138bc6195a..70baa169c7917 100644
--- a/lib/SIL/IR/OperandOwnership.cpp
+++ b/lib/SIL/IR/OperandOwnership.cpp
@@ -810,6 +810,7 @@ BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, GenericFRem)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, FSub)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, GenericFSub)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, Fence)
+BUILTIN_OPERAND_OWNERSHIP(TrivialUse, Freeze)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, Ifdef)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, GetObjCTypeEncoding)
 BUILTIN_OPERAND_OWNERSHIP(InstantaneousUse, ICMP_EQ)
diff --git a/lib/SIL/IR/ValueOwnership.cpp b/lib/SIL/IR/ValueOwnership.cpp
index c7ed8453476f0..24e21097abb4f 100644
--- a/lib/SIL/IR/ValueOwnership.cpp
+++ b/lib/SIL/IR/ValueOwnership.cpp
@@ -491,6 +491,7 @@ CONSTANT_OWNERSHIP_BUILTIN(None, FRem)
 CONSTANT_OWNERSHIP_BUILTIN(None, GenericFRem)
 CONSTANT_OWNERSHIP_BUILTIN(None, FSub)
 CONSTANT_OWNERSHIP_BUILTIN(None, GenericFSub)
+CONSTANT_OWNERSHIP_BUILTIN(None, Freeze)
 CONSTANT_OWNERSHIP_BUILTIN(None, ICMP_EQ)
 CONSTANT_OWNERSHIP_BUILTIN(None, ICMP_NE)
 CONSTANT_OWNERSHIP_BUILTIN(None, ICMP_SGE)
diff --git a/test/IRGen/builtin_freeze.swift b/test/IRGen/builtin_freeze.swift
new file mode 100644
index 0000000000000..8efc01616730e
--- /dev/null
+++ b/test/IRGen/builtin_freeze.swift
@@ -0,0 +1,52 @@
+// RUN: %target-swift-frontend -O -module-name builtin_freeze -enable-experimental-feature BuiltinModule -primary-file %s -emit-ir -o - | %FileCheck %s --check-prefix=CHECK
+
+import Builtin
+
+func fptosi(_ x: Float) -> Int32 {
+  Int32(Builtin.fptosi_FPIEEE32_Int32(x._value))
+  // CHECK: fptosi float %{{.+}} to i32
+}
+
+func fptosiWithFreeze(_ x: Float) -> Int32 {
+  Int32(Builtin.freeze_Int32(Builtin.fptosi_FPIEEE32_Int32(x._value)))
+  // CHECK: fptosi float %{{.+}} to i32
+  // CHECK-NEXT: freeze i32 %{{.+}}
+}
+
+func yuck() -> Int32 {
+  fptosi(0x1.0p32)
+  // CHECK: poison
+}
+
+func yum() -> Int32 {
+  fptosiWithFreeze(0x1.0p32)
+  // CHECK-NOT: poison
+}
+
+func fptosi(_ x: SIMD2<Float>) -> SIMD2<Int32> {
+  let maybePoison = Builtin.fptosi_Vec2xFPIEEE32_Vec2xInt32(x._storage._value)
+  var result = SIMD2<Int32>()
+  result._storage._value = maybePoison
+  return result
+  // CHECK: fptosi <2 x float> %{{.+}} to <2 x i32>
+}
+
+func fptosiWithFreeze(_ x: SIMD2<Float>) -> SIMD2<Int32> {
+  let maybePoison = Builtin.fptosi_Vec2xFPIEEE32_Vec2xInt32(x._storage._value)
+  let frozen = Builtin.freeze_Vec2xInt32(maybePoison)
+  var result = SIMD2<Int32>()
+  result._storage._value = frozen
+  return result
+  // CHECK: fptosi <2 x float> %{{.+}} to <2 x i32>
+  // CHECK-NEXT: freeze <2 x i32> %{{.+}}
+}
+
+func doubleYuck(_ x: SIMD2<Float>) -> SIMD2<Int32> {
+  fptosi(SIMD2<Float>(repeating: 0x1.0p32))
+  // CHECK: poison
+}
+
+func DoubleYum(_ x: SIMD2<Float>) -> SIMD2<Int32> {
+  fptosiWithFreeze(SIMD2<Float>(repeating: 0x1.0p32))
+  // CHECK-NOT: poison
+}