[BranchProbability] Remove the restriction that known and unknown probabilities canno...

The current BranchProbability::normalizeProbabilities() forbids known and
unknown probabilities to coexist in the list. This was once used to help
capture probability exceptions but has caused some reported build
failures (https://llvm.org/bugs/show_bug.cgi?id=25838).

This patch removes this restriction by evenly distributing the complement
of the sum of all known probabilities to unknown ones. We could still
treat this as an abnormal behavior, but it is better to emit warnings in
our future profile validator.

Differential revision: http://reviews.llvm.org/D15548

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255934 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Support/BranchProbability.h b/include/llvm/Support/BranchProbability.h
index 415805ce3971c20622b563db8957bf4616bb3fd9..1d6a7d84fbf47131edc20a558ed700e2531d31c9 100644 (file)
--- a/include/llvm/Support/BranchProbability.h
+++ b/include/llvm/Support/BranchProbability.h
@@ -183,17 +183,32 @@ void BranchProbability::normalizeProbabilities(ProbabilityIter Begin,
   if (Begin == End)
     return;
 
-  auto UnknownProbCount =
-      std::count(Begin, End, BranchProbability::getUnknown());
-  assert((UnknownProbCount == 0 ||
-          UnknownProbCount == std::distance(Begin, End)) &&
-         "Cannot normalize probabilities with known and unknown ones.");
-  (void)UnknownProbCount;
-
-  uint64_t Sum = std::accumulate(
-      Begin, End, uint64_t(0),
-      [](uint64_t S, const BranchProbability &BP) { return S + BP.N; });
-
+  unsigned UnknownProbCount = 0;
+  uint64_t Sum = std::accumulate(Begin, End, uint64_t(0),
+                                 [&](uint64_t S, const BranchProbability &BP) {
+                                   if (!BP.isUnknown())
+                                     return S + BP.N;
+                                   UnknownProbCount++;
+                                   return S;
+                                 });
+
+  if (UnknownProbCount > 0) {
+    BranchProbability ProbForUnknown = BranchProbability::getZero();
+    // If the sum of all known probabilities is less than one, evenly distribute
+    // the complement of sum to unknown probabilities. Otherwise, set unknown
+    // probabilities to zeros and continue to normalize known probabilities.
+    if (Sum < BranchProbability::getDenominator())
+      ProbForUnknown = BranchProbability::getRaw(
+          (BranchProbability::getDenominator() - Sum) / UnknownProbCount);
+
+    std::replace_if(Begin, End,
+                    [](const BranchProbability &BP) { return BP.isUnknown(); },
+                    ProbForUnknown);
+
+    if (Sum <= BranchProbability::getDenominator())
+      return;
+  }
+ 
   if (Sum == 0) {
     BranchProbability BP(1, std::distance(Begin, End));
     std::fill(Begin, End, BP);

diff --git a/unittests/Support/BranchProbabilityTest.cpp b/unittests/Support/BranchProbabilityTest.cpp
index 847661d21b38169a9790f15a4bc5a557e01ff7e0..e90e7f8ff11ac416f65536cdb9ec0003a14247f2 100644 (file)
--- a/unittests/Support/BranchProbabilityTest.cpp
+++ b/unittests/Support/BranchProbabilityTest.cpp
@@ -288,6 +288,7 @@ TEST(BranchProbabilityTest, scaleBruteForce) {
 }
 
 TEST(BranchProbabilityTest, NormalizeProbabilities) {
+  const auto UnknownProb = BranchProbability::getUnknown();
   {
     SmallVector<BranchProbability, 2> Probs{{0, 1}, {0, 1}};
     BranchProbability::normalizeProbabilities(Probs.begin(), Probs.end());
@@ -322,6 +323,36 @@ TEST(BranchProbabilityTest, NormalizeProbabilities) {
     EXPECT_EQ(BranchProbability::getDenominator() / 3 + 1,
               Probs[2].getNumerator());
   }
+  {
+    SmallVector<BranchProbability, 2> Probs{{0, 1}, UnknownProb};
+    BranchProbability::normalizeProbabilities(Probs.begin(), Probs.end());
+    EXPECT_EQ(0, Probs[0].getNumerator());
+    EXPECT_EQ(BranchProbability::getDenominator(), Probs[1].getNumerator());
+  }
+  {
+    SmallVector<BranchProbability, 2> Probs{{1, 1}, UnknownProb};
+    BranchProbability::normalizeProbabilities(Probs.begin(), Probs.end());
+    EXPECT_EQ(BranchProbability::getDenominator(), Probs[0].getNumerator());
+    EXPECT_EQ(0, Probs[1].getNumerator());
+  }
+  {
+    SmallVector<BranchProbability, 2> Probs{{1, 2}, UnknownProb};
+    BranchProbability::normalizeProbabilities(Probs.begin(), Probs.end());
+    EXPECT_EQ(BranchProbability::getDenominator() / 2, Probs[0].getNumerator());
+    EXPECT_EQ(BranchProbability::getDenominator() / 2, Probs[1].getNumerator());
+  }
+  {
+    SmallVector<BranchProbability, 4> Probs{
+        {1, 2}, {1, 2}, {1, 2}, UnknownProb};
+    BranchProbability::normalizeProbabilities(Probs.begin(), Probs.end());
+    EXPECT_EQ(BranchProbability::getDenominator() / 3 + 1,
+              Probs[0].getNumerator());
+    EXPECT_EQ(BranchProbability::getDenominator() / 3 + 1,
+              Probs[1].getNumerator());
+    EXPECT_EQ(BranchProbability::getDenominator() / 3 + 1,
+              Probs[2].getNumerator());
+    EXPECT_EQ(0, Probs[3].getNumerator());
+  }
 }
 
 }