Add checkMulAdd helper function to CheckedArithmetic

[george.karpenkov]

Summary

Multiplication followed by addition (https://en.wikipedia.org/wiki/Multiply–accumulate_operation) is a sufficiently common use-case to warrant a separate helper.

[NoQ]

llvm/include/llvm/Support/CheckedArithmetic.h

65–67

if (llvm::Optional<T> Product = checkedMul(A, B)) { ... }

llvm/include/llvm/Support/CheckedArithmetic.h

 /// Multiply two signed integers \p LHS and \p RHS, return wrapped result
 /// if available.
 template <typename T>
 typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
 checkedMul(T LHS, T RHS) {
   return checkedOp(LHS, RHS, &llvm::APInt::smul_ov);
 }
 
+/// Multiply A and B, and add C to the resulting product.
+/// Return the value if available, None if overflowing.
+template <typename T>
+typename std::enable_if<std::is_signed<T>::value, llvm::Optional<T>>::type
+checkedMulAdd(T A, T B, T C) {
+  llvm::Optional<T> Product = checkedMul(A, B);
+  if (Product)
+    return checkedAdd(*Product, C);
+  return llvm::None;
+}
+
 /// Add two unsigned integers \p LHS and \p RHS, return wrapped result
 /// if available.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
 checkedAddUnsigned(T LHS, T RHS) {
   return checkedOp(LHS, RHS, &llvm::APInt::uadd_ov, /*Signed=*/false);
 }
 
 /// Multiply two unsigned integers \p LHS and \p RHS, return wrapped result
 /// if available.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
 checkedMulUnsigned(T LHS, T RHS) {
   return checkedOp(LHS, RHS, &llvm::APInt::umul_ov, /*Signed=*/false);
 }
 
+/// Multiply unsigned A and B, and add C to the resulting product.
+/// Return the value if available, None if overflowing.
+template <typename T>
+typename std::enable_if<std::is_unsigned<T>::value, llvm::Optional<T>>::type
+checkedMulAddUnsigned(T A, T B, T C) {
+  llvm::Optional<T> Product = checkedMulUnsigned(A, B);
+  if (Product)
+    return checkedAddUnsigned(*Product, C);
+  return llvm::None;
+}
+
 } // End llvm namespace
 
 #endif

llvm/unittests/Support/CheckedArithmeticTest.cpp

TEST(CheckedArithmetic, CheckedMul) {
   const int64_t Max = std::numeric_limits<int64_t>::max();
   const int64_t Min = std::numeric_limits<int64_t>::min();
   EXPECT_EQ(checkedMul<int64_t>(Max, 2), None);
   EXPECT_EQ(checkedMul<int64_t>(Max, Max), None);
   EXPECT_EQ(checkedMul<int64_t>(Min, 2), None);
   EXPECT_EQ(checkedMul<int64_t>(10, 2), Optional<int64_t>(20));
 }
 
+TEST(CheckedArithmetic, CheckedMulAdd) {
+  const int64_t Max = std::numeric_limits<int64_t>::max();
+  const int64_t Min = std::numeric_limits<int64_t>::min();
+  EXPECT_EQ(checkedMulAdd<int64_t>(Max, 1, 2), None);
+  EXPECT_EQ(checkedMulAdd<int64_t>(1, 1, Max), None);
+  EXPECT_EQ(checkedMulAdd<int64_t>(1, -1, Min), None);
+  EXPECT_EQ(checkedMulAdd<int64_t>(10, 2, 3), Optional<int64_t>(23));
+}
+
 TEST(CheckedArithmetic, CheckedMulSmall) {
   const int16_t Max = std::numeric_limits<int16_t>::max();
   const int16_t Min = std::numeric_limits<int16_t>::min();
   EXPECT_EQ(checkedMul<int16_t>(Max, 2), None);
   EXPECT_EQ(checkedMul<int16_t>(Max, Max), None);
   EXPECT_EQ(checkedMul<int16_t>(Min, 2), None);
   EXPECT_EQ(checkedMul<int16_t>(10, 2), Optional<int16_t>(20));
 }
 
+TEST(CheckedArithmetic, CheckedMulAddSmall) {
+  const int16_t Max = std::numeric_limits<int16_t>::max();
+  const int16_t Min = std::numeric_limits<int16_t>::min();
+  EXPECT_EQ(checkedMulAdd<int16_t>(Max, 1, 2), None);
+  EXPECT_EQ(checkedMulAdd<int16_t>(1, 1, Max), None);
+  EXPECT_EQ(checkedMulAdd<int16_t>(1, -1, Min), None);
+  EXPECT_EQ(checkedMulAdd<int16_t>(10, 2, 3), Optional<int16_t>(23));
+}
+
 TEST(CheckedArithmetic, CheckedAddUnsigned) {
   const uint64_t Max = std::numeric_limits<uint64_t>::max();
   EXPECT_EQ(checkedAddUnsigned<uint64_t>(Max, Max), None);
   EXPECT_EQ(checkedAddUnsigned<uint64_t>(Max, 1), None);
   EXPECT_EQ(checkedAddUnsigned<uint64_t>(10, 1), Optional<uint64_t>(11));
 }
 
 TEST(CheckedArithmetic, CheckedMulUnsigned) {
   const uint64_t Max = std::numeric_limits<uint64_t>::max();
   EXPECT_EQ(checkedMulUnsigned<uint64_t>(Max, 2), llvm::None);
   EXPECT_EQ(checkedMulUnsigned<uint64_t>(Max, Max), llvm::None);
   EXPECT_EQ(checkedMulUnsigned<uint64_t>(10, 2), Optional<uint64_t>(20));
 }
 
+TEST(CheckedArithmetic, CheckedMulAddUnsigned) {
+  const uint64_t Max = std::numeric_limits<uint64_t>::max();
+  EXPECT_EQ(checkedMulAddUnsigned<uint64_t>(Max, 1, 2), None);
+  EXPECT_EQ(checkedMulAddUnsigned<uint64_t>(1, 1, Max), None);
+  EXPECT_EQ(checkedMulAddUnsigned<uint64_t>(10, 2, 3), Optional<uint64_t>(23));
+}
+
 
 } // namespace