Revert "Ensure that InstructionCost actually implements a total ordering"

This reverts commit b481cd519e07b3ad2bd3e81c89b0dd8efd68d6bc.

include/llvm/Support/InstructionCost.h

@@ -146,30 +146,31 @@ 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 !(*this < RHS) && !(RHS < *this);
+    return State == RHS.State && Value == RHS.Value;
   }
 
   bool operator!=(const InstructionCost &RHS) const { return !(*this == RHS); }
 
   bool operator==(const CostType RHS) const {
-    InstructionCost RHS2(RHS);
+    return State == Valid && Value == 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); }

unittests/Support/InstructionCostTest.cpp

@@ -25,7 +25,6 @@ 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);
@@ -38,9 +37,6 @@ 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);