[PATCH] D95803: Ensure that InstructionCost actually implements a total ordering

[Christopher Tetreault via Phabricator via llvm-commits]

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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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D95803

Files:
  llvm/include/llvm/Support/InstructionCost.h
  llvm/unittests/Support/InstructionCostTest.cpp


Index: llvm/unittests/Support/InstructionCostTest.cpp
===================================================================
--- llvm/unittests/Support/InstructionCostTest.cpp
+++ llvm/unittests/Support/InstructionCostTest.cpp
@@ -25,6 +25,7 @@
   InstructionCost VSix = 6;
   InstructionCost IThreeA = InstructionCost::getInvalid(3);
   InstructionCost IThreeB = InstructionCost::getInvalid(3);
+  InstructionCost ITwo = InstructionCost::getInvalid(2);
   InstructionCost TmpCost;
 
   EXPECT_NE(VThree, VNegTwo);
@@ -38,6 +39,11 @@
   EXPECT_EQ(VThree * VNegTwo, -6);
   EXPECT_EQ(VSix / VThree, 2);
 
+  EXPECT_TRUE((IThreeA < ITwo) || (IThreeA > ITwo) || (IThreeA == ITwo));
+  EXPECT_NE(IThreeA, ITwo);
+  EXPECT_LT(ITwo, IThreeA);
+  EXPECT_GT(IThreeA, ITwo);
+
   EXPECT_FALSE(IThreeA.isValid());
   EXPECT_EQ(IThreeA.getState(), InstructionCost::Invalid);
 
Index: llvm/include/llvm/Support/InstructionCost.h
===================================================================
--- llvm/include/llvm/Support/InstructionCost.h
+++ llvm/include/llvm/Support/InstructionCost.h
@@ -146,31 +146,30 @@
     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 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 true;
+
+    return Value < RHS.Value;
+  }
+
   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); }


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