[clang][bytecode] Optimize enum value range checks (#139672)

Only do the work if we really have to.

Author: tbaederr

clang/lib/AST/ByteCode/Interp.cpp

@@ -1251,12 +1251,11 @@ bool Free(InterpState &S, CodePtr OpPC, bool DeleteIsArrayForm,
 
 void diagnoseEnumValue(InterpState &S, CodePtr OpPC, const EnumDecl *ED,
                        const APSInt &Value) {
-  llvm::APInt Min;
-  llvm::APInt Max;
-
   if (S.EvaluatingDecl && !S.EvaluatingDecl->isConstexpr())
     return;
 
+  llvm::APInt Min;
+  llvm::APInt Max;
   ED->getValueRange(Max, Min);
   --Max;
 

clang/lib/AST/ByteCode/Interp.h

@@ -3026,10 +3026,11 @@ template <PrimType Name, class T = typename PrimConv<Name>::T>
 inline bool CheckEnumValue(InterpState &S, CodePtr OpPC, const EnumDecl *ED) {
   assert(ED);
   assert(!ED->isFixed());
-  const APSInt Val = S.Stk.peek<T>().toAPSInt();
 
-  if (S.inConstantContext())
+  if (S.inConstantContext()) {
+    const APSInt Val = S.Stk.peek<T>().toAPSInt();
     diagnoseEnumValue(S, OpPC, ED, Val);
+  }
   return true;
 }