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

llvm-svn: 197302

3 files changed, 23 insertions, 0 deletions

diff --git a/llvm/include/llvm/Support/BlockFrequency.h b/llvm/include/llvm/Support/BlockFrequency.h
index 997d11e47ab..dae520b54e4 100644
--- a/llvm/include/llvm/Support/BlockFrequency.h
+++ b/llvm/include/llvm/Support/BlockFrequency.h
@@ -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);
diff --git a/llvm/lib/Support/BlockFrequency.cpp b/llvm/lib/Support/BlockFrequency.cpp
index d1f8408dfcb..00cf75bd5cf 100644
--- a/llvm/lib/Support/BlockFrequency.cpp
+++ b/llvm/lib/Support/BlockFrequency.cpp
@@ -145,6 +145,18 @@ BlockFrequency::operator+(const BlockFrequency &Prob) const {
   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());
 }
diff --git a/llvm/unittests/Support/BlockFrequencyTest.cpp b/llvm/unittests/Support/BlockFrequencyTest.cpp
index ffdea2c1790..c3184515046 100644
--- a/llvm/unittests/Support/BlockFrequencyTest.cpp
+++ b/llvm/unittests/Support/BlockFrequencyTest.cpp
@@ -237,4 +237,12 @@ TEST(BlockFrequencyTest, ProbabilityCompare) {
   EXPECT_FALSE(BigZero >= BigOne);
 }
 
+TEST(BlockFrequencyTest, SaturatingRightShift) {
+  BlockFrequency Freq(0x10080ULL);
+  Freq >>= 2;
+  EXPECT_EQ(Freq.getFrequency(), 0x4020ULL);
+  Freq >>= 20;
+  EXPECT_EQ(Freq.getFrequency(), 0x1ULL);
+}
+
 }