[llvm] r197302 - [block-freq] Add a right shift to BlockFrequency that saturates at 1.

[Michael Gottesman]

Author: mgottesman
Date: Fri Dec 13 20:24:22 2013
New Revision: 197302

URL: http://llvm.org/viewvc/llvm-project?rev=197302&view=rev
Log:
[block-freq] Add a right shift to BlockFrequency that saturates at 1.

Modified:
    llvm/trunk/include/llvm/Support/BlockFrequency.h
    llvm/trunk/lib/Support/BlockFrequency.cpp
    llvm/trunk/unittests/Support/BlockFrequencyTest.cpp

Modified: llvm/trunk/include/llvm/Support/BlockFrequency.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/BlockFrequency.h?rev=197302&r1=197301&r2=197302&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/BlockFrequency.h (original)
+++ llvm/trunk/include/llvm/Support/BlockFrequency.h Fri Dec 13 20:24:22 2013
@@ -55,6 +55,9 @@ public:
   BlockFrequency &operator+=(const BlockFrequency &Freq);
   const BlockFrequency operator+(const BlockFrequency &Freq) const;
 
+  /// \brief Shift block frequency to the right by count digits saturating to 1.
+  BlockFrequency &operator>>=(const unsigned count);
+
   /// \brief Scale the given BlockFrequency by N/D. Return the remainder from
   /// the division by D. Upon overflow, the routine will saturate.
   uint32_t scale(const BranchProbability &Prob);

Modified: llvm/trunk/lib/Support/BlockFrequency.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/BlockFrequency.cpp?rev=197302&r1=197301&r2=197302&view=diff
==============================================================================
--- llvm/trunk/lib/Support/BlockFrequency.cpp (original)
+++ llvm/trunk/lib/Support/BlockFrequency.cpp Fri Dec 13 20:24:22 2013
@@ -145,6 +145,18 @@ BlockFrequency::operator+(const BlockFre
   return Freq;
 }
 
+BlockFrequency &BlockFrequency::operator>>=(const unsigned count) {
+  // Frequency can never be 0 by design.
+  assert(Frequency != 0);
+
+  // Shift right by count.
+  Frequency >>= count;
+
+  // Saturate to 1 if we are 0.
+  Frequency |= Frequency == 0;
+  return *this;
+}
+
 uint32_t BlockFrequency::scale(const BranchProbability &Prob) {
   return scale(Prob.getNumerator(), Prob.getDenominator());
 }

Modified: llvm/trunk/unittests/Support/BlockFrequencyTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/BlockFrequencyTest.cpp?rev=197302&r1=197301&r2=197302&view=diff
==============================================================================
--- llvm/trunk/unittests/Support/BlockFrequencyTest.cpp (original)
+++ llvm/trunk/unittests/Support/BlockFrequencyTest.cpp Fri Dec 13 20:24:22 2013
@@ -237,4 +237,12 @@ TEST(BlockFrequencyTest, ProbabilityComp
   EXPECT_FALSE(BigZero >= BigOne);
 }
 
+TEST(BlockFrequencyTest, SaturatingRightShift) {
+  BlockFrequency Freq(0x10080ULL);
+  Freq >>= 2;
+  EXPECT_EQ(Freq.getFrequency(), 0x4020ULL);
+  Freq >>= 20;
+  EXPECT_EQ(Freq.getFrequency(), 0x1ULL);
+}
+
 }