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Ensure that InstructionCost actually implements a total ordering

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Previously, operator== would consider the actual equality of the pairs
(lhs.Value, lhs.State) == (rhs.Value, rhs.State). However, if an invalid
cost was involved in a call to operator<, only the state would be
compared. Thus, it was not the case that ({2, Invalid} < {3, Invalid} ||
{2, Invalid} > {3, Invalid} || {2, Invalid} == {3, Invalid}).

This patch implements a true total ordering, where cost state is
considered first, then value. While it's not really imporant that
{2, Invalid} be considered to be less than {3, Invalid}, it's not a
problem either. This patch also implements operator== in terms of
operator<, so the two definitions will be kept in sync.

Reviewed By: sdesmalen

Differential Revision: https://reviews.llvm.org/D95803
This commit is contained in:
Christopher Tetreault 2021-02-02 09:14:55 -08:00
parent 63a3fb08ab
commit 21f48fe20a
2 changed files with 18 additions and 15 deletions
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29
include/llvm/Support/InstructionCost.h
View File

@ -146,31 +146,30 @@ 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 {
return State < RHS.State || 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); }

4
unittests/Support/InstructionCostTest.cpp
View File

@ -25,6 +25,7 @@ TEST_F(CostTest, Operators) {
InstructionCost VSix = 6;
InstructionCost IThreeA = InstructionCost::getInvalid(3);
InstructionCost IThreeB = InstructionCost::getInvalid(3);
InstructionCost ITwo = InstructionCost::getInvalid(2);
InstructionCost TmpCost;
EXPECT_NE(VThree, VNegTwo);
@ -37,6 +38,9 @@ TEST_F(CostTest, Operators) {
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);