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Reland "Ensure that InstructionCost actually implements a total ordering"

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The operator< in the previous attempt was incorrect. It is unfortunate
that this was only caught by the expensive checks.

This reverts commit ff1147c3635685ba6aefbdc9394300adb5404595.
This commit is contained in:
Christopher Tetreault 2021-02-03 06:40:03 -08:00
parent 6d08b0343e
commit 27e0b248a8
2 changed files with 33 additions and 17 deletions
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36
include/llvm/Support/InstructionCost.h
View File

@ -36,8 +36,8 @@ public:
enum CostState { Valid, Invalid };
private:
CostType Value;
CostState State;
CostType Value = 0;
CostState State = Valid;
void propagateState(const InstructionCost &RHS) {
if (RHS.State == Invalid)
@ -45,6 +45,7 @@ private:
}
public:
// A default constructed InstructionCost is a valid zero cost
InstructionCost() = default;
InstructionCost(CostState) = delete;
@ -146,31 +147,32 @@ public:
return Copy;
}
/// For the comparison operators we have chosen to use lexicographical
/// ordering where valid costs are always considered to be less than invalid
/// costs. This avoids having to add asserts to the comparison operators that
/// the states are valid and users can test for validity of the cost
/// explicitly.
bool operator<(const InstructionCost &RHS) const {
if (State != RHS.State)
return State < RHS.State;
return Value < RHS.Value;
}
// Implement in terms of operator< to ensure that the two comparisons stay in
// sync
bool operator==(const InstructionCost &RHS) const {
return State == RHS.State && Value == RHS.Value;
return !(*this < RHS) && !(RHS < *this);
}
bool operator!=(const InstructionCost &RHS) const { return !(*this == RHS); }
bool operator==(const CostType RHS) const {
return State == Valid && Value == RHS;
InstructionCost RHS2(RHS);
return *this == RHS2;
}
bool operator!=(const CostType RHS) const { return !(*this == RHS); }
/// For the comparison operators we have chosen to use total ordering with
/// the following rules:
/// 1. If either of the states != Valid then a lexicographical order is
/// applied based upon the state.
/// 2. If both states are valid then order based upon value.
/// This avoids having to add asserts the comparison operators that the states
/// are valid and users can test for validity of the cost explicitly.
bool operator<(const InstructionCost &RHS) const {
if (State != Valid || RHS.State != Valid)
return State < RHS.State;
return Value < RHS.Value;
}
bool operator>(const InstructionCost &RHS) const { return RHS < *this; }
bool operator<=(const InstructionCost &RHS) const { return !(RHS < *this); }

14
unittests/Support/InstructionCostTest.cpp
View File

@ -19,12 +19,21 @@ struct CostTest : public testing::Test {
} // namespace
TEST_F(CostTest, DefaultCtor) {
InstructionCost DefaultCost;
ASSERT_TRUE(DefaultCost.isValid());
EXPECT_EQ(*(DefaultCost.getValue()), 0);
}
TEST_F(CostTest, Operators) {
InstructionCost VThree = 3;
InstructionCost VNegTwo = -2;
InstructionCost VSix = 6;
InstructionCost IThreeA = InstructionCost::getInvalid(3);
InstructionCost IThreeB = InstructionCost::getInvalid(3);
InstructionCost ITwo = InstructionCost::getInvalid(2);
InstructionCost TmpCost;
EXPECT_NE(VThree, VNegTwo);
@ -33,10 +42,15 @@ TEST_F(CostTest, Operators) {
EXPECT_EQ(IThreeA, IThreeB);
EXPECT_GE(IThreeA, VNegTwo);
EXPECT_LT(VSix, IThreeA);
EXPECT_LT(VThree, ITwo);
EXPECT_GE(ITwo, VThree);
EXPECT_EQ(VSix - IThreeA, IThreeB);
EXPECT_EQ(VThree - VNegTwo, 5);
EXPECT_EQ(VThree * VNegTwo, -6);
EXPECT_EQ(VSix / VThree, 2);
EXPECT_NE(IThreeA, ITwo);
EXPECT_LT(ITwo, IThreeA);
EXPECT_GT(IThreeA, ITwo);
EXPECT_FALSE(IThreeA.isValid());
EXPECT_EQ(IThreeA.getState(), InstructionCost::Invalid);