[llvm] b481cd5 - Ensure that InstructionCost actually implements a total ordering
Christopher Tetreault via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 2 11:49:29 PST 2021
Author: Christopher Tetreault
Date: 2021-02-02T11:49:14-08:00
New Revision: b481cd519e07b3ad2bd3e81c89b0dd8efd68d6bc
URL: https://github.com/llvm/llvm-project/commit/b481cd519e07b3ad2bd3e81c89b0dd8efd68d6bc
DIFF: https://github.com/llvm/llvm-project/commit/b481cd519e07b3ad2bd3e81c89b0dd8efd68d6bc.diff
LOG: Ensure that InstructionCost actually implements a total ordering
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
Added:
Modified:
llvm/include/llvm/Support/InstructionCost.h
llvm/unittests/Support/InstructionCostTest.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Support/InstructionCost.h b/llvm/include/llvm/Support/InstructionCost.h
index fbc898b878bb..7101ed1c9365 100644
--- a/llvm/include/llvm/Support/InstructionCost.h
+++ b/llvm/include/llvm/Support/InstructionCost.h
@@ -146,31 +146,30 @@ class InstructionCost {
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); }
diff --git a/llvm/unittests/Support/InstructionCostTest.cpp b/llvm/unittests/Support/InstructionCostTest.cpp
index 8ba9f990f027..2a881a71e2e4 100644
--- a/llvm/unittests/Support/InstructionCostTest.cpp
+++ b/llvm/unittests/Support/InstructionCostTest.cpp
@@ -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);
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