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[BranchProbability] Remove the restriction that known and unknown probabilities cannot coexist when being normalized.

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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

llvm-svn: 255934
This commit is contained in:
Cong Hou
2015-12-17 22:27:07 +00:00
parent 8e9ba042a6
commit 7308f42d91
2 changed files with 55 additions and 9 deletions
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33
llvm/include/llvm/Support/BranchProbability.h
View File

@@ -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;
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;
});
uint64_t Sum = std::accumulate(
Begin, End, uint64_t(0),
[](uint64_t S, const BranchProbability &BP) { return S + BP.N; });
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);

31
llvm/unittests/Support/BranchProbabilityTest.cpp
View File

@@ -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());
}
}
}