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Implement comparison operators for BranchProbability in a way that can't overflow INT64_MAX.

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Add a test case for the edge case that triggers this. Thanks to Chandler for bringing this to my attention.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142794 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2011-10-24 13:50:56 +00:00
parent de1c9bb450
commit 13b10731ab
2 changed files with 27 additions and 10 deletions
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28
include/llvm/Support/BranchProbability.h
View File

@ -29,10 +29,6 @@ class BranchProbability {
// Denominator
uint32_t D;
int64_t compare(BranchProbability RHS) const {
return (uint64_t)N * RHS.D - (uint64_t)D * RHS.N;
}
public:
BranchProbability(uint32_t n, uint32_t d) : N(n), D(d) {
assert(d > 0 && "Denomiator cannot be 0!");
@ -54,12 +50,24 @@ public:
void dump() const;
bool operator==(BranchProbability RHS) const { return compare(RHS) == 0; }
bool operator!=(BranchProbability RHS) const { return compare(RHS) != 0; }
bool operator< (BranchProbability RHS) const { return compare(RHS) < 0; }
bool operator> (BranchProbability RHS) const { return compare(RHS) > 0; }
bool operator<=(BranchProbability RHS) const { return compare(RHS) <= 0; }
bool operator>=(BranchProbability RHS) const { return compare(RHS) >= 0; }
bool operator==(BranchProbability RHS) const {
return (uint64_t)N * RHS.D == (uint64_t)D * RHS.N;
}
bool operator!=(BranchProbability RHS) const {
return !(*this == RHS);
}
bool operator<(BranchProbability RHS) const {
return (uint64_t)N * RHS.D < (uint64_t)D * RHS.N;
}
bool operator>(BranchProbability RHS) const {
return RHS < *this;
}
bool operator<=(BranchProbability RHS) const {
return (uint64_t)N * RHS.D <= (uint64_t)D * RHS.N;
}
bool operator>=(BranchProbability RHS) const {
return RHS <= *this;
}
};
raw_ostream &operator<<(raw_ostream &OS, const BranchProbability &Prob);

9
unittests/Support/BlockFrequencyTest.cpp
View File

@ -71,6 +71,15 @@ TEST(BlockFrequencyTest, ProbabilityCompare) {
EXPECT_TRUE(B > C);
EXPECT_FALSE(B <= C);
EXPECT_TRUE(B >= C);
BranchProbability BigZero(0, UINT32_MAX);
BranchProbability BigOne(UINT32_MAX, UINT32_MAX);
EXPECT_FALSE(BigZero == BigOne);
EXPECT_TRUE(BigZero != BigOne);
EXPECT_TRUE(BigZero < BigOne);
EXPECT_FALSE(BigZero > BigOne);
EXPECT_TRUE(BigZero <= BigOne);
EXPECT_FALSE(BigZero >= BigOne);
}
}