diff --git a/llvm/include/llvm/ADT/StringExtras.h b/llvm/include/llvm/ADT/StringExtras.h
--- a/llvm/include/llvm/ADT/StringExtras.h
+++ b/llvm/include/llvm/ADT/StringExtras.h
@@ -66,10 +66,39 @@
 ///
 /// If \p C is not a valid hex digit, -1U is returned.
 inline unsigned hexDigitValue(char C) {
-  if (C >= '0' && C <= '9') return C-'0';
-  if (C >= 'a' && C <= 'f') return C-'a'+10U;
-  if (C >= 'A' && C <= 'F') return C-'A'+10U;
-  return -1U;
+  // clang-format off
+  static unsigned LUT[255] = {
+    /// 0-47: Non hexadecimal digits
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U,
+    /// 48-57: `0`-`9` hexadecimal digits
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
+    /// 58-64: Non hexadecimal digits
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    /// 65-70: `A`-`F` hexadecimal digits
+    10, 11, 12, 13, 14, 15,
+    /// 71-96: Non hexadecimal digits
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    /// 97-102: `a`-`f` hexadecimal digits
+    10, 11, 12, 13, 14, 15,
+    /// 103-255: Non hexadecimal digits
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U,
+    -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U, -1U
+  };
+  // clang-format on
+  return LUT[static_cast<unsigned char>(C)];
 }
 
 /// Checks if character \p C is one of the 10 decimal digits.
@@ -165,34 +194,61 @@
   return toHex(toStringRef(Input), LowerCase);
 }
 
-inline uint8_t hexFromNibbles(char MSB, char LSB) {
+inline bool tryGetHexFromNibbles(char MSB, char LSB, uint8_t &Hex) {
   unsigned U1 = hexDigitValue(MSB);
   unsigned U2 = hexDigitValue(LSB);
-  assert(U1 != -1U && U2 != -1U);
+  if (U1 == -1U || U2 == -1U)
+    return false;
 
-  return static_cast<uint8_t>((U1 << 4) | U2);
+  Hex = static_cast<uint8_t>((U1 << 4) | U2);
+  return true;
 }
-
-/// Convert hexadecimal string \p Input to its binary representation.
-/// The return string is half the size of \p Input.
-inline std::string fromHex(StringRef Input) {
+inline uint8_t hexFromNibbles(char MSB, char LSB) {
+  uint8_t Hex = 0;
+  bool GotHex = tryGetHexFromNibbles(MSB, LSB, Hex);
+  (void)GotHex;
+  assert(GotHex && "MSB and/or LSB do not correspond to hex digits");
+  return Hex;
+}
+
+/// Convert hexadecimal string \p Input to its binary representation and store
+/// the result in \p Output. Returns true if the binary representation could be
+/// converted from the hexadecimal string. Returns false if \p Input contains
+/// non-hexadecimal digits. The output string is half the size of \p Input.
+inline bool tryGetFromHex(StringRef Input, std::string &Output) {
   if (Input.empty())
-    return std::string();
+    return true;
 
-  std::string Output;
   Output.reserve((Input.size() + 1) / 2);
   if (Input.size() % 2 == 1) {
-    Output.push_back(hexFromNibbles('0', Input.front()));
+    uint8_t Hex = 0;
+    if (!tryGetHexFromNibbles('0', Input.front(), Hex))
+      return false;
+
+    Output.push_back(Hex);
     Input = Input.drop_front();
   }
 
   assert(Input.size() % 2 == 0);
   while (!Input.empty()) {
-    uint8_t Hex = hexFromNibbles(Input[0], Input[1]);
+    uint8_t Hex = 0;
+    if (!tryGetHexFromNibbles(Input[0], Input[1], Hex))
+      return false;
+
     Output.push_back(Hex);
     Input = Input.drop_front(2);
   }
-  return Output;
+  return true;
+}
+
+/// Convert hexadecimal string \p Input to its binary representation.
+/// The return string is half the size of \p Input.
+inline std::string fromHex(StringRef Input) {
+  std::string Hex;
+  bool GotHex = tryGetFromHex(Input, Hex);
+  (void)GotHex;
+  assert(GotHex && "Input contains non hex digits");
+  return Hex;
 }
 
 /// Convert the string \p S to an integer of the specified type using
diff --git a/llvm/unittests/ADT/StringExtrasTest.cpp b/llvm/unittests/ADT/StringExtrasTest.cpp
--- a/llvm/unittests/ADT/StringExtrasTest.cpp
+++ b/llvm/unittests/ADT/StringExtrasTest.cpp
@@ -89,6 +89,10 @@
   EXPECT_EQ(EvenStr, toHex(EvenData));
   EXPECT_EQ(EvenData, fromHex(EvenStr));
   EXPECT_EQ(StringRef(EvenStr).lower(), toHex(EvenData, true));
+
+  std::string InvalidStr = "A5ZX";
+  std::string IgnoredOutput;
+  EXPECT_FALSE(tryGetFromHex(InvalidStr, IgnoredOutput));
 }
 
 TEST(StringExtrasTest, to_float) {