diff --git a/llvm/include/llvm/ADT/APSInt.h b/llvm/include/llvm/ADT/APSInt.h
--- a/llvm/include/llvm/ADT/APSInt.h
+++ b/llvm/include/llvm/ADT/APSInt.h
@@ -29,10 +29,10 @@
 
   /// Create an APSInt with the specified width, default to unsigned.
   explicit APSInt(uint32_t BitWidth, bool isUnsigned = true)
-   : APInt(BitWidth, 0), IsUnsigned(isUnsigned) {}
+      : APInt(BitWidth, 0), IsUnsigned(isUnsigned) {}
 
   explicit APSInt(APInt I, bool isUnsigned = true)
-   : APInt(std::move(I)), IsUnsigned(isUnsigned) {}
+      : APInt(std::move(I)), IsUnsigned(isUnsigned) {}
 
   /// Construct an APSInt from a string representation.
   ///
@@ -85,12 +85,27 @@
   }
   using APInt::toString;
 
+  /// If this int is representable using an int64_t.
+  bool isRepresentableByInt64() const {
+    // For unsigned values with 64 active bits, they technically fit into a
+    // int64_t, but the user may get negative numbers and has to manually cast
+    // them to unsigned. Let's not bet the user has the sanity to do that and
+    // not give them a vague value at the first place.
+    return (isSigned() && getMinSignedBits() <= 64) ||
+           (!isSigned() && getActiveBits() <= 63);
+  }
+
   /// Get the correctly-extended \c int64_t value.
   int64_t getExtValue() const {
-    assert(getMinSignedBits() <= 64 && "Too many bits for int64_t");
+    assert(isRepresentableByInt64() && "Too many bits for int64_t");
     return isSigned() ? getSExtValue() : getZExtValue();
   }
 
+  std::optional<int64_t> tryExtValue() const {
+    return isRepresentableByInt64() ? std::optional<int64_t>(getExtValue())
+                                    : std::nullopt;
+  }
+
   APSInt trunc(uint32_t width) const {
     return APSInt(APInt::trunc(width), IsUnsigned);
   }
@@ -137,7 +152,7 @@
   APSInt operator>>(unsigned Amt) const {
     return IsUnsigned ? APSInt(lshr(Amt), true) : APSInt(ashr(Amt), false);
   }
-  APSInt& operator>>=(unsigned Amt) {
+  APSInt &operator>>=(unsigned Amt) {
     if (IsUnsigned)
       lshrInPlace(Amt);
     else
@@ -149,29 +164,27 @@
                       : APSInt(relativeAShr(Amt), false);
   }
 
-  inline bool operator<(const APSInt& RHS) const {
+  inline bool operator<(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
     return IsUnsigned ? ult(RHS) : slt(RHS);
   }
-  inline bool operator>(const APSInt& RHS) const {
+  inline bool operator>(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
     return IsUnsigned ? ugt(RHS) : sgt(RHS);
   }
-  inline bool operator<=(const APSInt& RHS) const {
+  inline bool operator<=(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
     return IsUnsigned ? ule(RHS) : sle(RHS);
   }
-  inline bool operator>=(const APSInt& RHS) const {
+  inline bool operator>=(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
     return IsUnsigned ? uge(RHS) : sge(RHS);
   }
-  inline bool operator==(const APSInt& RHS) const {
+  inline bool operator==(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
     return eq(RHS);
   }
-  inline bool operator!=(const APSInt& RHS) const {
-    return !((*this) == RHS);
-  }
+  inline bool operator!=(const APSInt &RHS) const { return !((*this) == RHS); }
 
   bool operator==(int64_t RHS) const {
     return compareValues(*this, get(RHS)) == 0;
@@ -196,10 +209,10 @@
   // signedness information.
 
   APSInt operator<<(unsigned Bits) const {
-    return APSInt(static_cast<const APInt&>(*this) << Bits, IsUnsigned);
+    return APSInt(static_cast<const APInt &>(*this) << Bits, IsUnsigned);
   }
-  APSInt& operator<<=(unsigned Amt) {
-    static_cast<APInt&>(*this) <<= Amt;
+  APSInt &operator<<=(unsigned Amt) {
+    static_cast<APInt &>(*this) <<= Amt;
     return *this;
   }
   APSInt relativeShl(unsigned Amt) const {
@@ -207,97 +220,99 @@
                       : APSInt(relativeAShl(Amt), false);
   }
 
-  APSInt& operator++() {
-    ++(static_cast<APInt&>(*this));
+  APSInt &operator++() {
+    ++(static_cast<APInt &>(*this));
     return *this;
   }
-  APSInt& operator--() {
-    --(static_cast<APInt&>(*this));
+  APSInt &operator--() {
+    --(static_cast<APInt &>(*this));
     return *this;
   }
   APSInt operator++(int) {
-    return APSInt(++static_cast<APInt&>(*this), IsUnsigned);
+    return APSInt(++static_cast<APInt &>(*this), IsUnsigned);
   }
   APSInt operator--(int) {
-    return APSInt(--static_cast<APInt&>(*this), IsUnsigned);
+    return APSInt(--static_cast<APInt &>(*this), IsUnsigned);
   }
   APSInt operator-() const {
-    return APSInt(-static_cast<const APInt&>(*this), IsUnsigned);
+    return APSInt(-static_cast<const APInt &>(*this), IsUnsigned);
   }
-  APSInt& operator+=(const APSInt& RHS) {
+  APSInt &operator+=(const APSInt &RHS) {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    static_cast<APInt&>(*this) += RHS;
+    static_cast<APInt &>(*this) += RHS;
     return *this;
   }
-  APSInt& operator-=(const APSInt& RHS) {
+  APSInt &operator-=(const APSInt &RHS) {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    static_cast<APInt&>(*this) -= RHS;
+    static_cast<APInt &>(*this) -= RHS;
     return *this;
   }
-  APSInt& operator*=(const APSInt& RHS) {
+  APSInt &operator*=(const APSInt &RHS) {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    static_cast<APInt&>(*this) *= RHS;
+    static_cast<APInt &>(*this) *= RHS;
     return *this;
   }
-  APSInt& operator&=(const APSInt& RHS) {
+  APSInt &operator&=(const APSInt &RHS) {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    static_cast<APInt&>(*this) &= RHS;
+    static_cast<APInt &>(*this) &= RHS;
     return *this;
   }
-  APSInt& operator|=(const APSInt& RHS) {
+  APSInt &operator|=(const APSInt &RHS) {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    static_cast<APInt&>(*this) |= RHS;
+    static_cast<APInt &>(*this) |= RHS;
     return *this;
   }
-  APSInt& operator^=(const APSInt& RHS) {
+  APSInt &operator^=(const APSInt &RHS) {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    static_cast<APInt&>(*this) ^= RHS;
+    static_cast<APInt &>(*this) ^= RHS;
     return *this;
   }
 
-  APSInt operator&(const APSInt& RHS) const {
+  APSInt operator&(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    return APSInt(static_cast<const APInt&>(*this) & RHS, IsUnsigned);
+    return APSInt(static_cast<const APInt &>(*this) & RHS, IsUnsigned);
   }
 
-  APSInt operator|(const APSInt& RHS) const {
+  APSInt operator|(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    return APSInt(static_cast<const APInt&>(*this) | RHS, IsUnsigned);
+    return APSInt(static_cast<const APInt &>(*this) | RHS, IsUnsigned);
   }
 
   APSInt operator^(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    return APSInt(static_cast<const APInt&>(*this) ^ RHS, IsUnsigned);
+    return APSInt(static_cast<const APInt &>(*this) ^ RHS, IsUnsigned);
   }
 
-  APSInt operator*(const APSInt& RHS) const {
+  APSInt operator*(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    return APSInt(static_cast<const APInt&>(*this) * RHS, IsUnsigned);
+    return APSInt(static_cast<const APInt &>(*this) * RHS, IsUnsigned);
   }
-  APSInt operator+(const APSInt& RHS) const {
+  APSInt operator+(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    return APSInt(static_cast<const APInt&>(*this) + RHS, IsUnsigned);
+    return APSInt(static_cast<const APInt &>(*this) + RHS, IsUnsigned);
   }
-  APSInt operator-(const APSInt& RHS) const {
+  APSInt operator-(const APSInt &RHS) const {
     assert(IsUnsigned == RHS.IsUnsigned && "Signedness mismatch!");
-    return APSInt(static_cast<const APInt&>(*this) - RHS, IsUnsigned);
+    return APSInt(static_cast<const APInt &>(*this) - RHS, IsUnsigned);
   }
   APSInt operator~() const {
-    return APSInt(~static_cast<const APInt&>(*this), IsUnsigned);
+    return APSInt(~static_cast<const APInt &>(*this), IsUnsigned);
   }
 
   /// Return the APSInt representing the maximum integer value with the given
   /// bit width and signedness.
   static APSInt getMaxValue(uint32_t numBits, bool Unsigned) {
     return APSInt(Unsigned ? APInt::getMaxValue(numBits)
-                           : APInt::getSignedMaxValue(numBits), Unsigned);
+                           : APInt::getSignedMaxValue(numBits),
+                  Unsigned);
   }
 
   /// Return the APSInt representing the minimum integer value with the given
   /// bit width and signedness.
   static APSInt getMinValue(uint32_t numBits, bool Unsigned) {
     return APSInt(Unsigned ? APInt::getMinValue(numBits)
-                           : APInt::getSignedMinValue(numBits), Unsigned);
+                           : APInt::getSignedMinValue(numBits),
+                  Unsigned);
   }
 
   /// Determine if two APSInts have the same value, zero- or
@@ -337,7 +352,7 @@
 
   /// Used to insert APSInt objects, or objects that contain APSInt objects,
   /// into FoldingSets.
-  void Profile(FoldingSetNodeID& ID) const;
+  void Profile(FoldingSetNodeID &ID) const;
 };
 
 inline bool operator==(int64_t V1, const APSInt &V2) { return V2 == V1; }
diff --git a/llvm/unittests/ADT/APSIntTest.cpp b/llvm/unittests/ADT/APSIntTest.cpp
--- a/llvm/unittests/ADT/APSIntTest.cpp
+++ b/llvm/unittests/ADT/APSIntTest.cpp
@@ -62,6 +62,13 @@
   EXPECT_EQ(UINT64_C(0) - 7, APSInt::getUnsigned(-7).getZExtValue());
 }
 
+TEST(APSIntTest, isRepresentableByInt64) {
+  ASSERT_TRUE(APSInt(APInt(3, 7), true).isRepresentableByInt64());
+  ASSERT_TRUE(APSInt(APInt(128, 7), true).isRepresentableByInt64());
+  ASSERT_TRUE(APSInt(APInt(128, 7), false).isRepresentableByInt64());
+  ASSERT_TRUE(APSInt(APInt(64, -1), false).isRepresentableByInt64());
+  ASSERT_FALSE(APSInt(APInt(64, (uint64_t)-1), true).isRepresentableByInt64());
+}
 TEST(APSIntTest, getExtValue) {
   EXPECT_TRUE(APSInt(APInt(3, 7), true).isUnsigned());
   EXPECT_TRUE(APSInt(APInt(3, 7), false).isSigned());
@@ -76,6 +83,12 @@
   EXPECT_EQ(9, APSInt(APInt(4, -7), true).getExtValue());
   EXPECT_EQ(-7, APSInt(APInt(4, -7), false).getExtValue());
 }
+TEST(APSIntTest, tryExtValue) {
+  ASSERT_EQ(-7, APSInt(APInt(64, -7), false).tryExtValue().value_or(42));
+  ASSERT_EQ(42, APSInt(APInt(128, -7), false).tryExtValue().value_or(42));
+  ASSERT_EQ(42, APSInt(APInt(64, -7), true).tryExtValue().value_or(42));
+  ASSERT_EQ(1, APSInt(APInt(128, 1), true).tryExtValue().value_or(42));
+}
 
 TEST(APSIntTest, compareValues) {
   auto U = [](uint64_t V) { return APSInt::getUnsigned(V); };