[llvm] r253412 - [llvm-profdata] Add SaturatingAdd/SaturatingMultiply Helper Functions
Sean Silva via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 17 20:04:06 PST 2015
On Tue, Nov 17, 2015 at 4:52 PM, Nathan Slingerland via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
> Author: slingn
> Date: Tue Nov 17 18:52:43 2015
> New Revision: 253412
>
> URL: http://llvm.org/viewvc/llvm-project?rev=253412&view=rev
> Log:
> [llvm-profdata] Add SaturatingAdd/SaturatingMultiply Helper Functions
>
> 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.
>
> No functional changes.
>
> Reviewers: dnovillo, bogner, davidxl
>
> Subscribers: davidxl, llvm-commits
>
> Differential Revision: http://reviews.llvm.org/D14720
>
> Modified:
> llvm/trunk/include/llvm/ProfileData/InstrProf.h
> llvm/trunk/include/llvm/ProfileData/SampleProf.h
> llvm/trunk/include/llvm/Support/MathExtras.h
> llvm/trunk/unittests/Support/MathExtrasTest.cpp
>
> Modified: llvm/trunk/include/llvm/ProfileData/InstrProf.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ProfileData/InstrProf.h?rev=253412&r1=253411&r2=253412&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/ProfileData/InstrProf.h (original)
> +++ llvm/trunk/include/llvm/ProfileData/InstrProf.h Tue Nov 17 18:52:43
> 2015
> @@ -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;
> }
>
> Modified: llvm/trunk/include/llvm/ProfileData/SampleProf.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ProfileData/SampleProf.h?rev=253412&r1=253411&r2=253412&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/ProfileData/SampleProf.h (original)
> +++ llvm/trunk/include/llvm/ProfileData/SampleProf.h Tue Nov 17 18:52:43
> 2015
> @@ -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.
>
> Modified: llvm/trunk/include/llvm/Support/MathExtras.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/MathExtras.h?rev=253412&r1=253411&r2=253412&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/MathExtras.h (original)
> +++ llvm/trunk/include/llvm/Support/MathExtras.h Tue Nov 17 18:52:43 2015
> @@ -653,6 +653,32 @@ inline int64_t SignExtend64(uint64_t X,
> 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
>
>
> Modified: llvm/trunk/unittests/Support/MathExtrasTest.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/MathExtrasTest.cpp?rev=253412&r1=253411&r2=253412&view=diff
>
> ==============================================================================
> --- llvm/trunk/unittests/Support/MathExtrasTest.cpp (original)
> +++ llvm/trunk/unittests/Support/MathExtrasTest.cpp Tue Nov 17 18:52:43
> 2015
> @@ -190,4 +190,52 @@ TEST(MathExtras, RoundUpToAlignment) {
> EXPECT_EQ(552u, RoundUpToAlignment(321, 255, 42));
> }
>
> +template<typename T>
> +void SaturatingAddTestHelper()
> +{
> + EXPECT_EQ(static_cast<T>(3),
> + SaturatingAdd(static_cast<T>(1), static_cast<T>(2)));
> + EXPECT_EQ(std::numeric_limits<T>::max(),
> + SaturatingAdd(std::numeric_limits<T>::max(),
> static_cast<T>(1)));
> + EXPECT_EQ(std::numeric_limits<T>::max(),
> + SaturatingAdd(static_cast<T>(1),
> std::numeric_limits<T>::max()));
> + EXPECT_EQ(std::numeric_limits<T>::max(),
> + SaturatingAdd(std::numeric_limits<T>::max(),
> + std::numeric_limits<T>::max()));
> +}
> +
> +TEST(MathExtras, SaturatingAdd) {
> + SaturatingAddTestHelper<uint8_t>();
> + SaturatingAddTestHelper<uint16_t>();
> + SaturatingAddTestHelper<uint32_t>();
> + SaturatingAddTestHelper<uint64_t>();
> +}
> +
> +template<typename T>
> +void SaturatingMultiplyTestHelper()
> +{
> + EXPECT_EQ(static_cast<T>(0),
> + SaturatingMultiply(static_cast<T>(1), static_cast<T>(0)));
> + EXPECT_EQ(static_cast<T>(0),
> + SaturatingMultiply(static_cast<T>(0), static_cast<T>(1)));
> + EXPECT_EQ(static_cast<T>(6),
> + SaturatingMultiply(static_cast<T>(2), static_cast<T>(3)));
> + EXPECT_EQ(std::numeric_limits<T>::max(),
> + SaturatingMultiply(std::numeric_limits<T>::max(),
> + static_cast<T>(2)));
> + EXPECT_EQ(std::numeric_limits<T>::max(),
> + SaturatingMultiply(static_cast<T>(2),
> + std::numeric_limits<T>::max()));
> + EXPECT_EQ(std::numeric_limits<T>::max(),
> + SaturatingMultiply(std::numeric_limits<T>::max(),
> + std::numeric_limits<T>::max()));
>
I think adding a helper:
T Max = std::numeric_limits<T>::max();
would help clean these up. Also, I think instead of `static_cast<T>(1)` you
can do just `T(1)`.
So for example that second-to-last one becomes:
EXPECT_EQ(Max, SaturatingMultiply(T(2), Max))
which seems like a nice improvement.
-- Sean Silva
> +}
> +
> +TEST(MathExtras, SaturatingMultiply) {
> + SaturatingMultiplyTestHelper<uint8_t>();
> + SaturatingMultiplyTestHelper<uint16_t>();
> + SaturatingMultiplyTestHelper<uint32_t>();
> + SaturatingMultiplyTestHelper<uint64_t>();
> +}
> +
> }
>
>
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