[Support] Change SaturatingAdd()/SaturatingMultiply() to use pointer for returning overflow state

Summary:
Improve SaturatingAdd()/SaturatingMultiply() to use bool * to optionally return overflow result.
This should make it clearer that the value is returned at callsites and reduces the size of the implementation.

Reviewers: davidxl, silvas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15219

llvm-svn: 255128

include/llvm/ProfileData/InstrProf.h

@@ -435,7 +435,7 @@ instrprof_error InstrProfRecord::merge(InstrProfRecord &Other) {
 
   for (size_t I = 0, E = Other.Counts.size(); I < E; ++I) {
     bool ResultOverflowed;
-    Counts[I] = SaturatingAdd(Counts[I], Other.Counts[I], ResultOverflowed);
+    Counts[I] = SaturatingAdd(Counts[I], Other.Counts[I], &ResultOverflowed);
     if (ResultOverflowed)
       Result = instrprof_error::counter_overflow;
   }

include/llvm/Support/MathExtras.h

@@ -659,38 +659,34 @@ inline int64_t SignExtend64(uint64_t X, unsigned B) {
 /// representable value of type T.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, T>::type
-SaturatingAdd(T X, T Y, bool &ResultOverflowed) {
+SaturatingAdd(T X, T Y, bool *ResultOverflowed = nullptr) {
+  bool Dummy;
+  bool &Overflowed = ResultOverflowed ? *ResultOverflowed : Dummy;
   // Hacker's Delight, p. 29
   T Z = X + Y;
-  ResultOverflowed = (Z < X || Z < Y);
+  Overflowed = (Z < X || Z < Y);
-  if (ResultOverflowed)
+  if (Overflowed)
     return std::numeric_limits<T>::max();
   else
     return Z;
 }
 
-/// \brief Add two unsigned integers, X and Y, of type T.
-/// Clamp the result to the maximum representable value of T on overflow.
-template <typename T>
-typename std::enable_if<std::is_unsigned<T>::value, T>::type
-SaturatingAdd(T X, T Y) {
-  bool ResultOverflowed;
-  return SaturatingAdd(X, Y, ResultOverflowed);
-}
-
 /// \brief Multiply two unsigned integers, X and Y, of type T.
 /// Clamp the result to the maximum representable value of T on overflow.
 /// ResultOverflowed indicates if the result is larger than the maximum
 /// representable value of type T.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, T>::type
-SaturatingMultiply(T X, T Y, bool &ResultOverflowed) {
+SaturatingMultiply(T X, T Y, bool *ResultOverflowed = nullptr) {
+  bool Dummy;
+  bool &Overflowed = ResultOverflowed ? *ResultOverflowed : Dummy;
+
   // Hacker's Delight, p. 30 has a different algorithm, but we don't use that
   // because it fails for uint16_t (where multiplication can have undefined
   // behavior due to promotion to int), and requires a division in addition
   // to the multiplication.
 
-  ResultOverflowed = false;
+  Overflowed = false;
 
   // Log2(Z) would be either Log2Z or Log2Z + 1.
   // Special case: if X or Y is 0, Log2_64 gives -1, and Log2Z
@@ -702,7 +698,7 @@ SaturatingMultiply(T X, T Y, bool &ResultOverflowed) {
     return X * Y;
   }
   if (Log2Z > Log2Max) {
-    ResultOverflowed = true;
+    Overflowed = true;
     return Max;
   }
 
@@ -711,7 +707,7 @@ SaturatingMultiply(T X, T Y, bool &ResultOverflowed) {
   // that on at the end.
   T Z = (X >> 1) * Y;
   if (Z & ~(Max >> 1)) {
-    ResultOverflowed = true;
+    Overflowed = true;
     return Max;
   }
   Z <<= 1;
@@ -721,15 +717,6 @@ SaturatingMultiply(T X, T Y, bool &ResultOverflowed) {
   return Z;
 }
 
-/// \brief Multiply two unsigned integers, X and Y, of type T.
-/// Clamp the result to the maximum representable value of T on overflow.
-template <typename T>
-typename std::enable_if<std::is_unsigned<T>::value, T>::type
-SaturatingMultiply(T X, T Y) {
-  bool ResultOverflowed;
-  return SaturatingMultiply(X, Y, ResultOverflowed);
-}
-
 extern const float huge_valf;
 } // End llvm namespace
 

unittests/Support/MathExtrasTest.cpp

@@ -197,23 +197,23 @@ void SaturatingAddTestHelper()
   bool ResultOverflowed;
 
   EXPECT_EQ(T(3), SaturatingAdd(T(1), T(2)));
-  EXPECT_EQ(T(3), SaturatingAdd(T(1), T(2), ResultOverflowed));
+  EXPECT_EQ(T(3), SaturatingAdd(T(1), T(2), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   EXPECT_EQ(Max, SaturatingAdd(Max, T(1)));
-  EXPECT_EQ(Max, SaturatingAdd(Max, T(1), ResultOverflowed));
+  EXPECT_EQ(Max, SaturatingAdd(Max, T(1), &ResultOverflowed));
   EXPECT_TRUE(ResultOverflowed);
 
   EXPECT_EQ(Max, SaturatingAdd(T(1), T(Max - 1)));
-  EXPECT_EQ(Max, SaturatingAdd(T(1), T(Max - 1), ResultOverflowed));
+  EXPECT_EQ(Max, SaturatingAdd(T(1), T(Max - 1), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   EXPECT_EQ(Max, SaturatingAdd(T(1), Max));
-  EXPECT_EQ(Max, SaturatingAdd(T(1), Max, ResultOverflowed));
+  EXPECT_EQ(Max, SaturatingAdd(T(1), Max, &ResultOverflowed));
   EXPECT_TRUE(ResultOverflowed);
 
   EXPECT_EQ(Max, SaturatingAdd(Max, Max));
-  EXPECT_EQ(Max, SaturatingAdd(Max, Max, ResultOverflowed));
+  EXPECT_EQ(Max, SaturatingAdd(Max, Max, &ResultOverflowed));
   EXPECT_TRUE(ResultOverflowed);
 }
 
@@ -232,45 +232,45 @@ void SaturatingMultiplyTestHelper()
 
   // Test basic multiplication.
   EXPECT_EQ(T(6), SaturatingMultiply(T(2), T(3)));
-  EXPECT_EQ(T(6), SaturatingMultiply(T(2), T(3), ResultOverflowed));
+  EXPECT_EQ(T(6), SaturatingMultiply(T(2), T(3), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   EXPECT_EQ(T(6), SaturatingMultiply(T(3), T(2)));
-  EXPECT_EQ(T(6), SaturatingMultiply(T(3), T(2), ResultOverflowed));
+  EXPECT_EQ(T(6), SaturatingMultiply(T(3), T(2), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   // Test multiplication by zero.
   EXPECT_EQ(T(0), SaturatingMultiply(T(0), T(0)));
-  EXPECT_EQ(T(0), SaturatingMultiply(T(0), T(0), ResultOverflowed));
+  EXPECT_EQ(T(0), SaturatingMultiply(T(0), T(0), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   EXPECT_EQ(T(0), SaturatingMultiply(T(1), T(0)));
-  EXPECT_EQ(T(0), SaturatingMultiply(T(1), T(0), ResultOverflowed));
+  EXPECT_EQ(T(0), SaturatingMultiply(T(1), T(0), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   EXPECT_EQ(T(0), SaturatingMultiply(T(0), T(1)));
-  EXPECT_EQ(T(0), SaturatingMultiply(T(0), T(1), ResultOverflowed));
+  EXPECT_EQ(T(0), SaturatingMultiply(T(0), T(1), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   EXPECT_EQ(T(0), SaturatingMultiply(Max, T(0)));
-  EXPECT_EQ(T(0), SaturatingMultiply(Max, T(0), ResultOverflowed));
+  EXPECT_EQ(T(0), SaturatingMultiply(Max, T(0), &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   EXPECT_EQ(T(0), SaturatingMultiply(T(0), Max));
-  EXPECT_EQ(T(0), SaturatingMultiply(T(0), Max, ResultOverflowed));
+  EXPECT_EQ(T(0), SaturatingMultiply(T(0), Max, &ResultOverflowed));
   EXPECT_FALSE(ResultOverflowed);
 
   // Test multiplication by maximum value.
   EXPECT_EQ(Max, SaturatingMultiply(Max, T(2)));
-  EXPECT_EQ(Max, SaturatingMultiply(Max, T(2), ResultOverflowed));
+  EXPECT_EQ(Max, SaturatingMultiply(Max, T(2), &ResultOverflowed));
   EXPECT_TRUE(ResultOverflowed);
 
   EXPECT_EQ(Max, SaturatingMultiply(T(2), Max));
-  EXPECT_EQ(Max, SaturatingMultiply(T(2), Max, ResultOverflowed));
+  EXPECT_EQ(Max, SaturatingMultiply(T(2), Max, &ResultOverflowed));
   EXPECT_TRUE(ResultOverflowed);
 
   EXPECT_EQ(Max, SaturatingMultiply(Max, Max));
-  EXPECT_EQ(Max, SaturatingMultiply(Max, Max, ResultOverflowed));
+  EXPECT_EQ(Max, SaturatingMultiply(Max, Max, &ResultOverflowed));
   EXPECT_TRUE(ResultOverflowed);
 
   // Test interesting boundary conditions for algorithm -
@@ -286,11 +286,11 @@ void SaturatingMultiplyTestHelper()
 
       if(OverflowExpected) {
         EXPECT_EQ(Max, SaturatingMultiply(X, Y));
-        EXPECT_EQ(Max, SaturatingMultiply(X, Y, ResultOverflowed));
+        EXPECT_EQ(Max, SaturatingMultiply(X, Y, &ResultOverflowed));
         EXPECT_TRUE(ResultOverflowed);
       } else {
         EXPECT_EQ(X * Y, SaturatingMultiply(X, Y));
-        EXPECT_EQ(X * Y, SaturatingMultiply(X, Y, ResultOverflowed));
+        EXPECT_EQ(X * Y, SaturatingMultiply(X, Y, &ResultOverflowed));
         EXPECT_FALSE(ResultOverflowed);
       }
     }