Add a division operator to BlockFrequency.

Allow a BlockFrequency to be divided by a non-zero BranchProbability
with saturating arithmetic. This will be used to compute the frequency
of a loop header given the probability of leaving the loop.

Our long division algorithm already saturates on overflow, so that was a
freebie.

llvm-svn: 185184

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/unittests/Support/BlockFrequencyTest.cpp b/llvm/unittests/Support/BlockFrequencyTest.cpp
index ff66bc4..4bcddfe 100644
--- a/llvm/unittests/Support/BlockFrequencyTest.cpp
+++ b/llvm/unittests/Support/BlockFrequencyTest.cpp
@@ -52,6 +52,24 @@ TEST(BlockFrequencyTest, MaxToMax) {
   EXPECT_EQ(Freq.getFrequency(), UINT64_MAX);
 }
 
+TEST(BlockFrequency, Divide) {
+  BlockFrequency Freq(0x3333333333333333ULL);
+  Freq /= BranchProbability(1, 2);
+  EXPECT_EQ(Freq.getFrequency(), 0x6666666666666666ULL);
+}
+
+TEST(BlockFrequencyTest, Saturate) {
+  BlockFrequency Freq(0x3333333333333333ULL);
+  Freq /= BranchProbability(100, 300);
+  EXPECT_EQ(Freq.getFrequency(), 0x9999999999999999ULL);
+  Freq /= BranchProbability(1, 2);
+  EXPECT_EQ(Freq.getFrequency(), UINT64_MAX);
+
+  Freq = 0x1000000000000000ULL;
+  Freq /= BranchProbability(10000, 160000);
+  EXPECT_EQ(Freq.getFrequency(), UINT64_MAX);
+}
+
 TEST(BlockFrequencyTest, ProbabilityCompare) {
   BranchProbability A(4, 5);
   BranchProbability B(4U << 29, 5U << 29);