[llvm-profdata] Add SaturatingAdd/SaturatingMultiply Helper Functions (2nd try)

Summary:
This change adds MathExtras helper functions for handling unsigned, saturating addition and multiplication. It also updates the instrumentation and sample profile merge implementations to use them.

Reviewers: dnovillo, bogner, davidxl

Subscribers: davidxl, llvm-commits

Differential Revision: http://reviews.llvm.org/D14720

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253497 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ProfileData/InstrProf.h

@@ -226,7 +226,7 @@ struct InstrProfValueSiteRecord {
       while (I != IE && I->Value < J->Value)
         ++I;
       if (I != IE && I->Value == J->Value) {
-        I->Count += J->Count;
+        I->Count = SaturatingAdd(I->Count, J->Count);
         ++I;
         continue;
       }

include/llvm/ProfileData/SampleProf.h

@@ -173,10 +173,7 @@ public:
   /// Sample counts accumulate using saturating arithmetic, to avoid wrapping
   /// around unsigned integers.
   void addSamples(uint64_t S) {
-    if (NumSamples <= std::numeric_limits<uint64_t>::max() - S)
-      NumSamples += S;
-    else
-      NumSamples = std::numeric_limits<uint64_t>::max();
+    NumSamples = SaturatingAdd(NumSamples, S);
   }
 
   /// Add called function \p F with samples \p S.
@@ -185,10 +182,7 @@ public:
   /// around unsigned integers.
   void addCalledTarget(StringRef F, uint64_t S) {
     uint64_t &TargetSamples = CallTargets[F];
-    if (TargetSamples <= std::numeric_limits<uint64_t>::max() - S)
-      TargetSamples += S;
-    else
-      TargetSamples = std::numeric_limits<uint64_t>::max();
+    TargetSamples = SaturatingAdd(TargetSamples, S);
   }
 
   /// Return true if this sample record contains function calls.

include/llvm/Support/MathExtras.h

@@ -653,6 +653,32 @@ inline int64_t SignExtend64(uint64_t X, unsigned B) {
   return int64_t(X << (64 - B)) >> (64 - B);
 }
 
+/// \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) {
+  // Hacker's Delight, p. 29
+  T Z = X + Y;
+  if (Z < X || Z < Y)
+    return std::numeric_limits<T>::max();
+  else
+    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) {
+  // Hacker's Delight, p. 30
+  T Z = X * Y;
+  if (Y != 0 && Z / Y != X)
+    return std::numeric_limits<T>::max();
+  else
+    return Z;
+}
+
 extern const float huge_valf;
 } // End llvm namespace
 

unittests/ProfileData/InstrProfTest.cpp

@@ -350,6 +350,38 @@ TEST_F(InstrProfTest, get_icall_data_merge1) {
   ASSERT_EQ(2U, VD_4[2].Count);
 }
 
+TEST_F(InstrProfTest, get_icall_data_merge1_saturation) {
+  const uint64_t Max = std::numeric_limits<uint64_t>::max();
+
+  InstrProfRecord Record1("caller", 0x1234, {1});
+  InstrProfRecord Record2("caller", 0x1234, {1});
+  InstrProfRecord Record3("callee1", 0x1235, {3, 4});
+
+  Record1.reserveSites(IPVK_IndirectCallTarget, 1);
+  InstrProfValueData VD1[] = {{(uint64_t) "callee1", 1}};
+  Record1.addValueData(IPVK_IndirectCallTarget, 0, VD1, 1, nullptr);
+
+  Record2.reserveSites(IPVK_IndirectCallTarget, 1);
+  InstrProfValueData VD2[] = {{(uint64_t) "callee1", Max}};
+  Record2.addValueData(IPVK_IndirectCallTarget, 0, VD2, 1, nullptr);
+
+  Writer.addRecord(std::move(Record1));
+  Writer.addRecord(std::move(Record2));
+  Writer.addRecord(std::move(Record3));
+
+  auto Profile = Writer.writeBuffer();
+  readProfile(std::move(Profile));
+
+  // Verify saturation of counts.
+  ErrorOr<InstrProfRecord> R = Reader->getInstrProfRecord("caller", 0x1234);
+  ASSERT_TRUE(NoError(R.getError()));
+  ASSERT_EQ(1U, R.get().getNumValueSites(IPVK_IndirectCallTarget));
+  std::unique_ptr<InstrProfValueData[]> VD =
+          R.get().getValueForSite(IPVK_IndirectCallTarget, 0);
+  ASSERT_EQ(StringRef("callee1"), StringRef((const char *)VD[0].Value, 7));
+  ASSERT_EQ(Max, VD[0].Count);
+}
+
 TEST_F(InstrProfTest, get_max_function_count) {
   InstrProfRecord Record1("foo", 0x1234, {1ULL << 31, 2});
   InstrProfRecord Record2("bar", 0, {1ULL << 63});

unittests/Support/MathExtrasTest.cpp

@@ -190,4 +190,40 @@ TEST(MathExtras, RoundUpToAlignment) {
   EXPECT_EQ(552u, RoundUpToAlignment(321, 255, 42));
 }
 
+template<typename T>
+void SaturatingAddTestHelper()
+{
+  const T Max = std::numeric_limits<T>::max();
+  EXPECT_EQ(T(3), SaturatingAdd(T(1), T(2)));
+  EXPECT_EQ(Max, SaturatingAdd(Max, T(1)));
+  EXPECT_EQ(Max, SaturatingAdd(T(1), Max));
+  EXPECT_EQ(Max, SaturatingAdd(Max, Max));
+}
+
+TEST(MathExtras, SaturatingAdd) {
+  SaturatingAddTestHelper<uint8_t>();
+  SaturatingAddTestHelper<uint16_t>();
+  SaturatingAddTestHelper<uint32_t>();
+  SaturatingAddTestHelper<uint64_t>();
+}
+
+template<typename T>
+void SaturatingMultiplyTestHelper()
+{
+  const T Max = std::numeric_limits<T>::max();
+  EXPECT_EQ(T(0), SaturatingMultiply(T(1), T(0)));
+  EXPECT_EQ(T(0), SaturatingMultiply(T(0), T(1)));
+  EXPECT_EQ(T(6), SaturatingMultiply(T(2), T(3)));
+  EXPECT_EQ(Max, SaturatingMultiply(Max, T(2)));
+  EXPECT_EQ(Max, SaturatingMultiply(T(2),Max));
+  EXPECT_EQ(Max, SaturatingMultiply(Max, Max));
+}
+
+TEST(MathExtras, SaturatingMultiply) {
+  SaturatingMultiplyTestHelper<uint8_t>();
+  SaturatingMultiplyTestHelper<uint16_t>();
+  SaturatingMultiplyTestHelper<uint32_t>();
+  SaturatingMultiplyTestHelper<uint64_t>();
+}
+
 }