[Support] Make getMaxValue and getMinValue constexpr variables (NFC)

This patch makes getMaxValue and getMinValue constexpr variables and
"inlines" the calls to getMaxValue and getMinValue.

We could probably make InstructionCost constexpr also, but that's left
for another day.

Author: kazutakahirata

llvm/include/llvm/Support/InstructionCost.h

@@ -59,8 +59,10 @@ class InstructionCost {
       State = Invalid;
   }
 
-  static CostType getMaxValue() { return std::numeric_limits<CostType>::max(); }
-  static CostType getMinValue() { return std::numeric_limits<CostType>::min(); }
+  static inline constexpr CostType MaxValue =
+      std::numeric_limits<CostType>::max();
+  static inline constexpr CostType MinValue =
+      std::numeric_limits<CostType>::min();
 
 public:
   // A default constructed InstructionCost is a valid zero cost
@@ -69,8 +71,8 @@ class InstructionCost {
   InstructionCost(CostState) = delete;
   InstructionCost(CostType Val) : Value(Val), State(Valid) {}
 
-  static InstructionCost getMax() { return getMaxValue(); }
-  static InstructionCost getMin() { return getMinValue(); }
+  static InstructionCost getMax() { return MaxValue; }
+  static InstructionCost getMin() { return MinValue; }
   static InstructionCost getInvalid(CostType Val = 0) {
     InstructionCost Tmp(Val);
     Tmp.setInvalid();
@@ -102,7 +104,7 @@ class InstructionCost {
     // Saturating addition.
     InstructionCost::CostType Result;
     if (AddOverflow(Value, RHS.Value, Result))
-      Result = RHS.Value > 0 ? getMaxValue() : getMinValue();
+      Result = RHS.Value > 0 ? MaxValue : MinValue;
 
     Value = Result;
     return *this;
@@ -120,7 +122,7 @@ class InstructionCost {
     // Saturating subtract.
     InstructionCost::CostType Result;
     if (SubOverflow(Value, RHS.Value, Result))
-      Result = RHS.Value > 0 ? getMinValue() : getMaxValue();
+      Result = RHS.Value > 0 ? MinValue : MaxValue;
     Value = Result;
     return *this;
   }
@@ -138,9 +140,9 @@ class InstructionCost {
     InstructionCost::CostType Result;
     if (MulOverflow(Value, RHS.Value, Result)) {
       if ((Value > 0 && RHS.Value > 0) || (Value < 0 && RHS.Value < 0))
-        Result = getMaxValue();
+        Result = MaxValue;
       else
-        Result = getMinValue();
+        Result = MinValue;
     }
 
     Value = Result;